Red, green and blue phosphorescent organic light-emitting diodes with ITO-free anode material

Journal Pre-proof Red, green and blue phosphorescent organic light-emitting diodes with ITO-free anode material Jayaraman Jayabharathi, Sekar Sivaraj, Venugopal Thanikachalam, Sekar Panimozhi, Jagathratchagan Anudeebhana

PII:

S1010-6030(19)31424-8

DOI:

https://doi.org/10.1016/j.jphotochem.2019.112229

Reference:

JPC 112229

To appear in:

Journal of Photochemistry & Photobiology, A: Chemistry

Received Date:

20 August 2019

Revised Date:

12 October 2019

Accepted Date:

7 November 2019

Please cite this article as: Jayabharathi J, Sivaraj S, Thanikachalam V, Panimozhi S, Anudeebhana J, Red, green and blue phosphorescent organic light-emitting diodes with ITO-free anode material, Journal of Photochemistry and amp; Photobiology, A: Chemistry (2019), doi: https://doi.org/10.1016/j.jphotochem.2019.112229

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

Red, green and blue phosphorescent organic light-emitting diodes with ITO-free anode material Jayaraman Jayabharathi*, Sekar Sivaraj, Panimozhi, Jagathratchagan Anudeebhana

Venugopal

Thanikachalam,

Sekar

Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India E-mail: [email protected].

Jo

ur

na

lP

re

-p

ro of

Graphical Abstract

Highlights 

Non-productive hole-current from RGB phosphorescent OLEDs was reduced by employing Ag NPs embedded glass:Ni-Ag-ZnO (SNSZO) anode enhanced the efficiencies



Blue device using SNSZO: Ir(fdbdi)3 exhibit maximum L- 42683 cd/m2, ηc- 43.6cd/A and ηp-45.3 lmW-1 with ηex- 20.2 %.



Green device with SNSZO: Ir(mnmpdi)2(acac) exhibit higher efficiency; L - 47238

ro of

cd/m2, ηc -50.9 cd/A, ηp - 49. lm w-1 and ηex - 18.9% [ITO: Ir(mnmpdi)2(acac): L39326 cd/m2; ηc-46.0 cd/A; ηp -39.3 lm w-1; ηex -13.8 %]. 

Red device (620 nm) with SNSZO: Ir(mnpbi)2(acac) show L - 9058 cd/m2, ηc - 8.3

-p

cd/A, ηp -6.4 lm w-1 and ηex - 12.2 % [ITO: Ir(mnpbi)2(acac): L- 7632 cd/m2; ηc -4.1 cd/A; ηp -6.40 lm w-1; ηex -6.0 %].

The proposed OLEDs with SNSZO anode shows excellent efficiencies than ITO and

re



na

lP

providing alternate for high-performance OLEDs and other optoelectronic devices.

ur

Abstract

The non-productive hole-current from blue, green and red phosphorescent OLEDs

Jo

was reduced by employing silver nanoparticles embedded glass:Ni-Ag-codoped ZnO (SNSZO) anode and enhanced the efficiencies. The blue device using SNSZO: Ir(fdbdi)3 exhibit maximum luminance (L) of 42683 cd/m2, current efficiency (ηc) of 43.6 cd/A and power efficiency (ηp) of 45.3 lm W-1 with external quantum efficiency (ηex) of 20.2 % than ITO: Ir(fdbdi)3 based device [L- 35126 cd/m2; ηc - 38.4 cd/A; ηp - 37.3 lm w-1; ηex -15.1 %]. The green device with SNSZO: Ir(mnmpdi)2(acac) show intensified emission at 520 nm and

exhibit higher efficiency; L - 47238 cd/m2, ηc -50.9 cd/A, ηp - 49.3 lm w-1 and ηex - 18.9 % [ITO: Ir(mnmpdi)2(acac): L- 39326 cd/m2; ηc-46.0 cd/A; ηp -39.3 lm w-1; ηex -13.8 %]. The red device (620 nm) with SNSZO: Ir(mnpbi)2(acac) show L - 9058 cd/m2, ηc - 8.3 cd/A, ηp 6.4 lm w-1 and ηex - 12.2 % [ITO: Ir(mnpbi)2(acac): L- 7632 cd/m2; ηc -4.1 cd/A; ηp -6.40 lm w-1; ηex -6.0 %]. The proposed OLEDs with SNSZO anode shows excellent efficiencies than ITO and providing alternate for high-performance OLEDs and other optoelectronic devices.

ro of

Keywords: Glass: Ni-Ag-codoped ZnO interface; anode material; maximum efficiencies;

-p

surface Plasmon.

re

1. Introduction

lP

Organic light-emitting diodes (OLEDs) are an emerging technology in displays, efficient lighting panels etc., [1-3]. The potential application of TCO (transparent conducting oxide) thin film in OLEDs, transparent thin film transistors, flat panel displays etc., have

na

inspired in technological research because of appreciable transparency with high conductivity [4]. In addition to cost-effect, stability and resistant of ITO, TCO work function (wf) must be

ur

appropriate for display applications [1]. Although the commercial TCO are dominated by

Jo

ITO, ITO usage on flexible devices is limited because of brittleness, high resistance at low temperature etc., [5-8]. To overcome the inflexibility of ITO, alternatives to ITO was developed with good electrical and optical property, such as grapheme [9], carbon nanotubes, metal nanowires [10-12], TCO nanocrystal [13], conducting polymer and metal-mesh TCEs [14-17]. A wide band gap ZnO is a promising material for TCO thin film due to non-toxic and inexpensive in comparison to ITO. However, high wf ~4.0 eV of ZnO leads to high

electron- injection barrier (EIB) between ZnO film and adjacent organic functional layer [18]. Numerous studies show that metal doped ZnO display promising electrical, magnetic and optical properties and adopted as an alternative electron injection layer (EIL) for air-stable OLEDs [19-21]. Silver doped ZnO is a promising EIL for efficient hybrid organic−inorganic OLEDs owing to improved energy level alignment [22]. The surface-plasmon of noble-metal nanostructures enhanced the optoelectronic device efficiencies [23-28]. The OLED efficiency have been increased by reducing hole-injection barrier (HIB) using embedded noble-metal

ro of

nano semiconductors; interface has been stabilized via tuning HIL [29-31] by forming electrical double layer on anode with suitable HIL [32]. The high energy barrier between ITO and EHOMO of organic materials prevents effective hole injection from ITO into organic layer

-p

and minimized the efficiency The wf of ITO has been increased by using ozone, plasma, wet and self-assembly monolayer coating treatment [33-38]. The Ni-doped ITO enhanced the

re

hole injection and enhanced the efficiency and only few reports on RGB PHOLEDs with

lP

ZnO as anode [39-43]. Therefore, we aimed to enhance the performance of red, green and blue phosphorescent OLEDs using silver NPs sandwiched between Ni-Ag-codoped ZnO NPs (SNSZO) and glass substrate with Ir(mnpbi)2(acac), Ir(mnmpdi)2(acac) and Ir(fdbdi)3 as

2. Experimental

na

efficient red, green and blue emitters, respectively.

ur

2.1. Characterization

Jo

H-1 and C-13 NMR spectra were recorded on Bruker 400 MHz spectrometer using TMS as internal standard and mass spectra was recorded on Agilent LCMS VL SD. The the Uv optical spectra were measured on Lambda 35 PerkinElmer (solution)/ Lambda 35 spectrophotometer with integrated sphere (RSA-PE-20) (film) instrument. The emission spectra was analyzed with Perkin Elmer LS55 fluorescence spectrometer measurements. Oxidation

potentials

of

emissive

materials

were

measured

from

potentiostat

electrochemical analyzer (CHI 630A). The absolute quantum yield of solution and film were measured with fluorescence spectrometer Model-F7100 with integrating sphere. Thermal properties decomposition (Td) and glass transition (Tg) temperature was measured with Perkin Elmer thermal analysis system (10° C min-1; N2 flow rate - 100 ml min-1) and NETZSCH (DSC-204) (10° C min-1; N2 atmosphere), respectively. The composition of Ag NPs and NSZO NPs was confirmed with XPS (X-ray photoelectron spectra: ESCA-3 Mark II spectrometer-VG - Al Kα (1486.6 eV) radiation). SEM (scanning electron microscopic

ro of

images) images and EDS (energy dispersive X-ray spectra) were recorded using JSM-5610 equipped with back electron (BE) detector and FEI Quanta FEG, respectively. The TEM (transmission electron microscopy) image was obtained on Philips TEM with 200 kV

-p

electron beam and SAED (selected area electron diffraction) pattern was recorded from Philips TEM (CCD camera; 200 kV). The powder XRD was obtained with INEL EQINOX

re

1000 POWDER XRD (Cu Kα rays; 1.5406 Å; current - 30 mA; 40 kV).

lP

2.2. Fabrication of HyLEDs

Newly synthesized iridium (III) complexes namely, Ir(mnpbi)2(acac), Ir(mnmpdi)2 (acac) and Ir(fdbdi)3 are employed as RGB emitters, respectively. The fabrication was made

na

by using vacuum deposition (5 x 10-6 torr) over ITO-coated glass with 20 /square resistance. Organic substances deposition was made on ITO with a rate of 1–2 Å s−1 and LiF

ur

was evaporated thermally over organic surface. The CIE, EL spectra and luminance

Jo

characteristics were recorded with USB-650-VIS-NIR spectrometer (Ocean Opitics, Inc, USA). The thickness was determined with quartz crystal thickness monitor and current density (J)voltage (V) and luminance (L)-voltage (V) were performed using Keithley 2450 source meter. 2.3. Computational Details

The optimized geometry, HOMO and LUMO contour map of Ir(fdbdi)3, Ir(mnmpdi)2 (acac) and Ir(mnpbi)2(acac) were studied with Guassian-09 [44]. 2.4. Synthesis of Ni-Ag-codoped ZnO (NSZO) To zinc acetate (0.1g) solution with AgNO3 and Ni(NO3)2·6H2O in 10 ml PVP K30(0.01 M), 1:1 aqueous ammonia solution was added, under continuous stirring for 30 min to maintain pH 7. The formed white gel was subjected to age overnight, then the precipitate was filtered and washed by using ethanol and water, dried at 80 °C (10 h) and calcinated to

ro of

get grey solid, at 500 °C (6 h; heating rate 10 °C min-1). 2.5. Synthesis of silver nanoparticles (Ag NPs)

The M. elengi fruit pericarp powder was extracted with water and filtered through

-p

membrane filter paper (0.22 μm cellulose nitrate). The extract was stirred with aqueous 10 ml AgNO3 (0.01 M) at 60 °C for 1 h and formed Ag NPs solution was stored at 5 °C [45].

re

2.6. 2-(1-methoxynaphthalen-4-yl)-1-(4-methoxyphenyl)-4,5-diphenyl-1H-imidazole (mnmpdi)

lP

Mixture of benzil (5 mmol), 4-methoxynaphthaldehyde (5 mmol), 4-methoxyaniline (6 mmol) and ammonium acetate (61 mmol) was refluxed (ethanol: 12 h: N2 stream). From

na

the chilled solution, yellow solid of mnmpdi was separated. 1H NMR (400 MHz, CDCl3):  3.75 (s, 6H), 6.80 (d, J=8.8 Hz, 2H), 7.28-7.32 (m, 7H), 7.34-7.45 (m, 8H), 7.78 (d, J=8.6

ur

Hz, 2H), 8.14 (d, J=8.2 Hz, 1H) (Figure S1). 13C NMR (100 MHz, CDCl3):  55.86, 56.38, 104.85, 115.43, 122.39, 123.03, 128.42, 128.59, 129.66, 135.36, 136.88, 138.98, 149.51,

Jo

160.67 (Figure S1). MS: m/z. 482.11 [M+]. calcd. 482.20 (Figure S7). 2.7. Iridium(III)–bis–2-(1-methoxynaphthalen-4-yl)-1-(4-methoxynaphthyl)-4,5-diphenyl 1H-imidazole(acetylacetonate) [Ir(mnmpdi)2 (acac)] The mnmpdi (2.2 mmol) and iridium (III) chloride trihydrate (1 mmol) in 2-ethoxyethanol: H2O (3:1) was refluxed (N2, 120 ºC), the formed dimer (1 mmol) was refluxed (120 °C; N2) with K2CO3 (2.5 mmol) and acetylacetone (2.2 mmol) in

ethoxyethanol (5 ml) [46]. The green coloured acetylacetonate iridium complex was characterized by spectral techniques 1H NMR (400 MHz, CDCl3):  1.29 (s, 6H), 3.79 (s, 12H), 5.26 (s, 1H), 6.75 (d, J=8.4 Hz, 4H), 6.8-7.09 (m, 6H) 7.11 (d, J=8.4 Hz, 4H), 7.267.38 (m, 14H), 7.66-7.70 (m, 4H) 8.28 (d, J=8.2 Hz, 2H) (Figure S2). 13C NMR (100 MHz, CDCl3):  25.28, 43.32, 55.82, 104.68, 113.69, 114.12, 115.26, 119.82, 122.56, 128.35, 129.62, 130.29, 135.29, 137.51, 138.91, 151.64, 160.84(Figure S2). MS: m/z. 1257.28 [M+]. calcd. 1257.41 (Figure S7).

ro of

2.8. 2-(4-fluorostyryl)-1-(2, 3-dihydrobenzo[b][1,4]dioxin-8-yl)-1H-imidazole (fdbdi)

A mixture of (E)-3-(4-fluorophenyl)acrylaldehyde (1 mmol), glyoxal (1 mmol), 2,3dihydro-1,4- benzodioxane-6-amine (1 mmol) and ammonium acetate (1mmol) in ethanol

-p

was refluxed (12 h; N2). The mixture was cooled, filtered and column chromatographed (9:1, benzene: ethyl acetate as eluent) (Scheme 1). Yield: 65%.

1

H NMR (400 MHz, CDCl3): 

re

4.39 (s, 4H), 6.72 (d, J=16.4 Hz, 1H), 6.92 (t, 3H), 6.99 (d, J=8.4 Hz, 1H), 7.29-7.41 (m, 13

C NMR (100 MHz, CDCl3): 64.35, 113.52,

lP

5H), 7.54 (d, J=16.0 Hz, 1H) (Figure S3).

114.53, 115.13, 116.37, 121.86, 125.48, 128.09, 130.08, 130.19, 133.46,137.25,147.69,

na

162.21(Figure S3). MS: m/z. 322.06 [M+] calcd. 322.11 (Figure S7). 2.9. fac-tris[2-(4-fluorostyryl)-1-(2,3-dihydrobenzo[b][1,4]dioxin-8-yl)-1H-imidazolynato -C2, N1]iridium(III) [Ir(fdbdi)3] mixture

of

ur

A

2-(4-fluorostyryl)-1-(2,3-dihydrobenzo[b][1,4]dioxin-8-yl)-1H-

Jo

imidazole (fdbdi) (7.83 mmol), iridium(III) trisacetylacetonate (1.56 mmol) and glycerol (9 ml) was refluxed (240°C; N2; 48 h). After cooling, the reaction mixture was extracted with dichloromethane, after evaporation the separated fac-isomer Ir(fdbdi)3 was purified by haxane washing. 1H NMR (400 MHz, CDCl3):  4.45 (s, 12H), 6.72-6.74 (m, 9H),6.92 (d, J=16.4 Hz, 2H), 7.11 (d, J=8.4 Hz, 4H), 7.21 (d, J=8.2 Hz, 3H), 7.28-7.35 (m, 9H), 7.51 (d, J=8.4 Hz, 3H) (Figure S4).13C NMR (100 MHz, CDCl3): 64.35, 115.42, 121.93, 125.08, 128.02,

130.46, 137.18, 147.69, 162.56(Figure S4). MS: m/z. 1156.27 [M+]; calcd. 1156.12 (Figure S7). 2.10. 2-(1-methoxynaphthalen-4-yl)-1-phenyl-1H-benzo[d]imidazole (mnpbi) A mixture of 4-methoxynaphthaldehyde (2 mmol) and N-phenyl-o-phenylenediamine (1mmol) (2.5 mmol) was refluxed at 80ºC in ethanol. The reaction mixture was extracted and purified by column chromatography (9:1 petroleum ether: ethyl acetate). Yield: 33%. 1H NMR (CDCl3):  3.78 (s, 3H), 6.65 (d, J = 7.8 Hz, 1H), 7.28 (d, J = 8.0 Hz, 2H), 7.32-7.54 13

ro of

(m, 6H), 7.56-7.58 (m, 4H), 7.62-7.71 (m, 1H), 8.25 (d, J = 7.4 Hz, 1H) (Figure S5).

C

NMR (100 MHz, CDCl3): 4.85, 11.75, 56.31, 105.23, 122.28, 123.82, 125.48, 126.68, 127.79, 128.26, 131.21, 134.28, 144.35, 156.52(Figure S5). MS: m/z. 350.02 [M+] calcd.

-p

350.14 (Figure S7).

2.11. Iridium (III)–bis–2- (1-methoxynaphthalen-4-yl) -1-phenyl-1H-benzo [d] imidazole

re

(acetylacetonate) [(mnpbi)2Ir(acac)]

lP

The mnpbi (2.2 mmol) and iridium (III) chloride trihydrate (1 mmol) in 2ethoxyethanol: H2O (3:1) was refluxed (120 ºC: N2 stream). The dimer (1 mmol) was refluxed with potassium carbonate (2.5 mmol) and acetylacetone (2.2 mmol) in 2-

na

ethoxyethanol (15 ml). The filtered iridium(III) complex, Ir(mnpbi)2 (acac) was purified by washings and used as emissive layer in fabrication of red OLEDs. Yield: 40%. 1H NMR

ur

(CDCl3):  1.28-1.34 (m, 6H), 3.78 (s, 6H), 5.05 (s, 1H), 6.59 (d, J = 8.4 Hz, 2H), 6.64 (d, J

Jo

= 7.2 Hz, 8H), 7.29-7.44 (m, 12H), 7.51 (d, J = 8.4 Hz, 2H), 7.71 (d, J = 8.8 Hz, 2H) 8.198.24 (m, 2H) (Figure S6). 13C NMR (100 MHz, CDCl3): 25.96, 43.67, 50.14, 64.35, 104.38, 115.42, 121.93, 122.34, 125.08, 126.59, 128.02, 130.46, 135.62, 137.18, 147.69, 156.56(Figure S6). MS: m/z. 993.21 [M+]; calcd. 993.30 (Figure S7). 3. Results and Discussion 3.1. Characterisation of Ni-Ag-codoped ZnO (NSZO)

XRD pattern of as-synthesized Ni-Ag-codoped ZnO (NSZO) shows three sets of XRD pattern: unmarked peak were indexed to hexagonal primitive ZnO structure corresponding to JCPDS (65-3411), the ∆ labelled peaks are assigned to face centered cubic silver corresponding to JCPDS (89-3722) [47, 48] and * labelled peaks were due to face centered cubic nickel [JCPDS (04-0850)]. After Ag and Ni anchoring, XRD pattern of ZnO was similar which reveal that nickel and silver was not integrated into ZnO lattice because of larger ionic radius of Ag (144 pm) and Ni (125 pm) than Zn2+ (74 pm), therefore, silver and

ro of

nickel metallic phase was formed on ZnO surface. The crystallite size of NSZO was calculated from Scherrer formula as ~11.60 nm and surface area as 90.99 m2 g-1 [49]. The increased NSZO crystallite size might be due to anchoring of Ag and Ni on the surface of

-p

ZnO. The weak and broad Ag (111) and Ni (311) peak (Figure 1) indicating a small size and well dispersed Ag and Ni on ZnO surface which is in consistent with HRTEM image. The

re

lattice spacing 0.20 nm, 0.52 nm and 0.24 nm, respectively corresponds to Ni (111), ZnO

lP

(001) and Ag (200) planes, respectively [50,51]. The average size of NSZO estimated as 12 nm from TEM image confirm that NSZO are nanoparticles with spherical shape. The rings in

na

SAED image fit with hexagonal ZnO and the SAED pattern (Figure 2) reveal that NSZO NPs are polycrystalline in nature with (100), (002), (110), (103), (001) and (211) planes for ZnO

ur

NPs, respectively [52, 53] and the SAED pattern is well agreement with XRD pattern. The XRD of Ag NPs synthesised from M. elengi fruit pericarp with interplanar

Jo

reflection of 38.12º (1 1 1), 44.30º (2 0 0), 64.44º (2 2 0), 77.40º (3 1 1) and 81.54º (2 2 2) corresponds to face centered cubic crystal (Figure 1: JCPDS. No. 87-0597) [54-57]. The crystal size of Ag NPs is estimated as 18.45 nm and the surface area as 57.21 m2/g. The TEM image shows the spherical nature of Ag NPs (Figure 2). The fringe distance 2.4 Å with spacing between (111) plane corresponds to FCC silver crystal and SAED pattern confirm its crystalline nature (Figure 2). The diffraction circles with bright spots in SAED pattern are

identified to (111), (200), (220), (311) and (222) planes of FCC silver which is in agreement with XRD results. The DLS images show the average size of Ag NPs and NSZO as 18.45 and 11.60 nm, respectively which is in consistent with the size calculated from XRD and TEM. The negative ζ potential of Ag NPs (-18.45 mV) and SSNSZO (-11.60 mV)] indicates the repulsive forces between the particles due to the electrical charge on the surface of Ag NPs and NSZO which in turn increase the stability(Figure S8). The chemical composition and oxidation state of NSZO was analysed by XPS which

ro of

shows the presence of Zn, Ag, Ni, O and C elements (Figure 3). The peak at 284.3 eV (C 1s) is due to residual carbon of the sample and hydrocarbon of XPS instrument. The binding energy of NSZO was different from pristine material reveal that strong interaction between

-p

Ag, Ni and ZnO NPs. The core level Ag 3d spectrum of NSZO showing two individual peaks at 367.3 eV for Ag 3d5/2 and at 372.3 for Ag 3d3/2. The reduction of Ag ion to metallic silver

re

was evidenced by 5 eV splitting between the two peaks. Moreover, the binding energy of Ag

lP

3d5/2 for NSZO is shifted to lower binding energy compared to metallic Ag (Ag0 -368.5 eV) indicates decrease in electron density of Ag [58, 59]: after deposition of Ag NPs on ZnO surface, electrons at Ag:ZnO interface leads to downward band- bending of ZnO side, leads

na

to electron transfer from silver nanodeposit to ZnO side [60]. Since Ag Fermi level is higher than ZnO Fermi level, the Ag work function is smaller than that of ZnO. Hence, electrons

ur

from Ag easily to transfer to CB ZnO during the Ag-doped ZnO formation and shifting ZnO

Jo

Fermi level to higher simultaneously lowering Ag Fermi level results in an equivalent Fermi level, hence, easy charge-transfer from silver nanodeposit to ZnO side (Figure 4) [61]. The peak at 1020 eV for Zn 2p3/2 and 1042 eV for Zn 2p1/2 reveal that Zn present as Zn+2 in NSZO [58, 59]. The peak at 528.7 and 530.6 eV reveal that O1s profile is asymmetric and assigned to lattice oxygen and surface hydroxyl groups, respectively. The peak at 852.1 eV is attributed to metallic nickel [62]. The composition of Ag NPs was identified by XPS (Figure

S8). The peak at 284.3 eV (C 1s) is due to residual carbon of the sample and hydrocarbon of XPS instrument. Binding energy peaks observed for Ag 3d5/2 and 3d3/2 are at 368.5 and 372.1 eV, respectively and is attributed to metallic silver [63]. The two symmetrical peaks namely, α and β at 528.0 and 531.8 eV reveal that O1s profile is asymmetric. The EDX of Ni-Agcodoped ZnO and Ag NPs confirm the constituent elements (Figure 2). The diffuse reflectance spectra (DRS) of zinc oxide and Ni-Ag-doped ZnO nanomaterials are presented in Figure 4. The absorption band at 472 nm is attributed to the

ro of

surface plasmon resonance of metallic silver nanodeposit on the particles. The reflectance data are reported as F(R) values, obtained by the application of the Kubelka–Munk algorithm [F(R) = (1 – R)2/2R]. Figure 4a shows transformation of DRS of ZnO by co-doping with

-p

nickel and silver: doping shifts absorption-edge to visible region. From the direct (F(R)hν)2 Vs photon energy] and indirect [(F(R)hν)0.5 Vs photon energy], energy gap (Eg) of Ni-Ag-

re

doped ZnO NPs was calculated as 3.03 eV (3.14 eV - ZnO) and 2.98 eV (3.10 eV - ZnO),

lP

respectively [22]. Figure 4a shows transformation of DRS of ZnO by co-doping with nickel and silver: doping shifts absorption-edge to visible region. From the direct (F(R)hv)2 versus photon energy] and indirect [(F(R)hv)0.5 versus photon energy], the energy gap (Eg) of Ni-Ag-

na

doped ZnO NPs was calculated as 3.03 eV (3.14 eV - ZnO) and 2.98 eV (3.10 eV - ZnO), respectively. The interaction of Ag and nickel with ZnO host generates a new energy donor

ur

level that leads to reduce the optical band gap [22]. The ZnO and Ni-Ag-doped ZnO exhibit

Jo

NBE around 422 nm and deep level emission around 510 nm (Figure 4). The NBE is due to excitonic- recombination whereas DLE is due to recombination of electron (singly occupiedoxygen vacancies) with hole (photogenerated) in VB. Doping leads to reduction of band gap, however, emission energy was unchanged due to quenching of free excitations [64]. Copper doping (potentiometric method [65]), silver doping (electrodeposition [66], chemical synthesis [67] and hydrothermal method [68]) of ZnO exhibit red-shifted emission whereas

nickel and silver doping by sol-gel method does not show red-shifted emission, but emission intensity is decreased due to SPR effect of Ag deposit. 3.2. Characterization of emissive materials Figure 5 represents the ORTEP of 2-(1-methoxynaphthalen-4-yl)-1-(4-methoxy phenyl)-4,5-diphenyl-1H-imidazole (mnmpdi): it is monoclinic crystal and crystallizes in the space group C2/c with cell dimensions, a = 26.5867(10) Å, b = 10.4284(3) Å, c = 22.5353(9) Å. The imidazole unit is planar and form dihedral angles of 79.5º and 68.7º with adjacent

ro of

methoxynaphthyl and p-methoxyphenyl ring [C(5)-N(2)-C(19)-C(4) = 79.5º; N(1)-C(12)-C(17)C(19) = 68.7º], respectively. The dihedral angle C(17)-C(19)-N(1)-C(4) between methoxynaphthyl and p-methoxyphenyl ring is 1.0º (Table S1): mnmpdi based iridium (III) complex Ir(mnmpdi)2

-p

(acac) is used as green emissive material in electroluminescent process. The broad phosphorescence spectra/quantum yield was measured as 510 nm/0.79 for Ir(mnmpdi)2

re

(acac), 615 nm/0.70 for Ir(mnpbi)2 (acac) and 440 nm/0.95 for Ir(fdbdi)3. The optical spectra

lP

(λabs) of iridium(III) complexes namely, Ir(fdbdi)3, Ir(mnmpdi)2 (acac) and Ir(mnpbi)2(acac) in CH2Cl2 (Figure 6). The absorption of heteroleptic iridium complexes [Ir(mnmpdi)2 (acac)252 nm and Ir(mnpbi)2(acac)- 280 nm) is assigned to π-π* transition ( same energy of free

na

ligands mnmpdi and mpbi), the absorption of homoleptic complex Ir(fdbdi)3 at 262 nm is assinged to spin-allowed ligand- centered transition. The other two bands at 363 & 318 nm

ur

for Ir(mnmpdi)2 (acac), 318 & 402 nm for Ir(mnpbi)2(acac) and 340 & 390 nm for Ir(fdbdi)3

Jo

is due to MLCT transitions (1MLCT←S0 and 3MLCT←S0). The intensity of 3MLCT←S0 is in close with 1MLCT←S0 which reveal that 3MLCT←S0 is symmetry allowed by spin-orbit coupling [69-74]. The three phosphors Ir(fdbdi)3, Ir(mnmpdi)2 (acac) and Ir(mnpbi)2(acac) show strong luminescence in solution and soild. The wave function (Φ) of the triplet state (ΦT) of Ir(fdbdi)3, Ir(mnmpdi)2 (acac) and Ir(mnpbi)2(acac) is a mixture of ΦT (π- π*) and ΦT (MLCT) [75-81], ΦT = a ΦT(π- π*) + b ΦT(MLCT), [a and b are normalized co-efficients, ΦT

(π- π*) and ΦT (MLCT) are wave function of 3(π- π*) and 3(MLCT) excited states, respectively]. When a > b, triplet state is dominated by 3π- π*; when b > a, triplet state is dominated by 3MLCT excited state. The higher contribution of 3MLCT in excited state was confirmed by the broad shape of emission spectra. The Franck-Condon electronic transitions explains the intensity of electronic transition from vibrational level of triplet state (3MLCT or 3

π- π*) to ground state (S0):dominant intensity from υ’0 → υ0 transition of 3MLCT / 3π- π* →

S0 whereas a shoulder peak with lower intensity derived from υ’0 → υ1 electronic transition

correlated to the intensities of vibration from excited 𝑀𝜔𝛥𝑄2 2ℎ

𝑛!

, S - Huang-Rhys factor,

MLCT/ 3π-π* state to ground state

: ω - vibrational frequency, M - reduced mass, ΔQ - displacement of potential

-p

(S0), S =

3

𝑒 −𝑠 𝑆 𝑛

ro of

(Figure S8). The gain in intensity is expressed as, I0→𝑛 =

energy surfaces between the S0 and excited state. The structural distortion upon excitation is

of

vibronic

emission

I0→0

spectra

of

.

iridium

complexes

[Ir(fdbdi)3,

lP

Absence

I0→1

re

explained by the ratio of height of two emission peaks, S =

Ir(mnmpdi)2(acac) and Ir(mnpbi)2(acac)] supports MLCT emission. This is confirmed by phosphorescence life time of Ir(fdbdi)3 (1.6 μs), Ir(mnmpdi)2(acac) (2.9 μs) and

na

Ir(mnpbi)2(acac) (2.0 μs)] (Figure 6). The broad emission spectra reveal that the excited triplet state of Ir(fdbdi)3, Ir(mnmpdi)2(acac) and Ir(mnpbi)2(acac) possess dominant

3

MLCT

ur

character. The radiative/ non-radiative (kr/ (knr) decay rate constants have been calculated

Jo

from,  = ISC {kr/(kr + knr)}, kr = /τ, knr = (1/τ) - (/τ) and τ = (kr + knr)-1 [ - quantum yield; τ - lifetime; ISC - intersystem-crossing yield]. The calculated kr/knr, 7.0/0.9 - Ir(fdbdi)3 3.0/0.9-Ir(mnmpdi)2(acac) and 3.7/1.8 -Ir(mnpbi)2(acac) reveal that radiative emission is predominant over non-radiative transition. The electrochemical stability of the complexes was confirmed by reversible oneelectron oxidation wave (Figure 6). The HOMO energy of Ir(fdbdi)3, Ir(mnmpdi)2(acac) and

Ir(mnpbi)2(acac) was measured to be -5.38, -5.10 and -5.12 eV, respectively [78] [EHOMO (eV) = -(Eox + 4.8)] whereas the LUMO energy was measured as -2.20, -2.30 and -2.78 eV [ELUMO = EHOMO –1239/λonset ] (Table 1). The HOMO orbital of Ir(mnmpdi)2(acac) is localized on iridium, methoxynaphthaldehyde and anizidine fragments whereas the LUMO orbital is populated on anizidine ring. The HOMO of Ir(fdbdi)3 is populated on iridium and imidazole fragments and in LUMO the electron density is localized on

side capping,

dihydrobenzodioxane fragment. The HOMO orbital of Ir(mnpbi)2(acac) is populated on

ro of

iridium and naphthaldehyde fragments and imidazole core whereas the LUMO orbital is partially populated on ancillary ligand. To test their suitability for device fabrication, the thermal characterization (Td) of Ir(fdbdi)3, Ir(mnmpdi)2(acac) and Ir(mnpbi)2(acac) was

-p

analyzed by TGA measurement. The TGA of Ir(fdbdi)3, Ir(mnmpdi)2(acac) and Ir(mnpbi)2(acac) exhibits high decomposition temperature (Td) of 423, 430 and 452 °C,

re

respectively (Figure 6). The higher decomposition of RGB emissive materials supports the

lP

suitability of these materials for fabrication of OLEDs and show higher efficiency at low turn on voltage.

The optimized geometry of Ir(mnmpdi)2(acac) and Ir(mnpbi)2(acac) exhibit a

na

distorted octahedral geometry around iridium atom with two imidazole ligands and one acetylacetonate (acac) ancillary ligand. The imidazole ligands adopt eclipsed configuration

ur

with two imidazole nitrogen atoms resides at trans-N,N chelate disposition. The

Jo

cyclometalated carbon atoms lies cis around iridium atom. From the optimized geometry (Figure 5) it was shown that Ir-Cav bond length is shorter than Ir-Nav bond length: Ir(fdbdi)3 [Ir-Cav-1.97 Å ˂ Ir-Nav -2.08 Å], Ir(mnmpdi)2(acac) [Ir-Cav-1.98Å ˂ Ir-Nav -2.10Å] and Ir(mnpbi)2(acac) [Ir-Cav-1.99 Å ˂ Ir-Nav -2.12 Å] [79, 80]. The stronger ligand Ir-C bonding interaction weakens Ir-C bonds at their trans disposition, electron rich phenyl rings show

strong influence, shows trans- effect, thus trans-C, C geometry is higher in energy thermodynamically and more labile kinetically called transphobia [81-82]. 3.3. Blue, green and red phosphorescent OLEDs The surface morphology of uniformly coated ITO with 1.0, 2.0 and 3.0 % concentration of SNSZO was analysed through atomic force microscopy (Figure S8). The thickness and RMS of SNSZO layer are 24, 28 and 34 nm and 2.86, 2.56 and 2.31 nm, respectively. The RMS roughness of SNSZO film was much smoother than ITO (4.47 nm) and it was decreased

ro of

slightly as the concentration of SNSZO film increased. As thickness of SNSZO increases, the lifetime also increases [1.50 ns (0%); 2.13 ns (1.0 %); 2.41 ns (2.0 %) and 2.58 ns (3.0 %)] (Figure S8). The 3.0 % wt SNSZO blocks exciton quenching effectively by surface

-p

quenching or non-radiative energy transfer quenching mechanism (Figure S9) and increase of lifetime indicate that quenching of excitons is reduced and the radiative decay of excitons is

re

increased.

lP

Thin film of Ag NPs embedded NSZO on glass show broad surface plasmon resonance at 432 nm. The emission intensity of glass/ Ag (2 nm)/ NSZO (60 nm)/ NPB (35 nm)/ CBP: iridium complex (25 nm)/ LiF (1 nm)/ Al (100 nm) film is stronger than the

na

device, glass/ NPB (40 nm)/ CBP: iridium complex (25 nm)/ LiF (1 nm)/ Al (100 nm) (Figure 7). The SPR of NPs enhanced the emissive material PL intensity and leads to increased

ur

absorption of incident light by concentrating electromagnetic field at hot spot: overlap of

Jo

SPR of nanoparticles with emission of emissive layer also enhanced the PL intensity (Figures 6 ). Hence, new born metal NPs are appropriate for OLEDs using homoleptic and heteroleptic iridium complexes as emissive layer (λabs -432 nm of SNSZO overlaps with λemi of emissive layer). The relative EL/ PL enhancement compared with control device pointed out that enhanced light -extraction from fabricated devices could be a major reason for the enhanced efficiency of the devices The RGB PHOLEDs were fabricated using Ir(fdbdi)3;

Ir(mnmpdi)2(acac); Ir(mnpbi)2(acac) emitters, respectively (Figure 7).Furthermore, the N,N′dicarbazolyl-4,4′-biphenyl (CBP) was employed as host material (wide energy gap & bipolartransport material) allowing effective e− − h+ recombination in the respective emissive layer. High triplet energy (2.3 eV) of HTM namely, N, N’-bis(naphthyl)-N,N`-diphenyl-1,1’biphenyl-4,4’-diamine (NPB) facilitates high energy exciton confinement [20]. The RMS of silver embedded SNZO is higher than ITO (Figure S8). The heat conductivity of Ag NPs is higher than ITO results large grain on SNSZO surface: the work function (EF) of Ag NPs :

ro of

NSZO interlayer will be stabilized than EF of ITO and increases the conductivity and EF of SNSZO surface leads to enhancing efficiencies (ηc, ηp & ηex) (Table 2). The current density and luminance of the devices increased with embedded Ag NPs at the interface of glass:

-p

SNSZO than reference devices without SNSZO (II, IV and VI). Among the blue devices I (449 nm: Figure 8) and II (465 nm), the blue emitting device with SNSZO: Ir(fdbdi)3 exhibit

re

maximum luminance (L) of 42683 cd/m2, current efficiency (ηc) of 43.6 cd/A and power

lP

efficiency (ηp) of 45.3 lm W-1 and external quantum efficiency (ηex) of 20.2 % than ITO: Ir(fdbdi)3 based device [L -35126 cd/m2; ηc -38.4 cd/A; ηp -37.3 lm w-1; ηex -15.1 %; V-3.2] at driving voltage 3.0 V. Similar observations were found for green and red devices. The green

na

device with emissive layer SSNSZO: Ir(mnmpdi)2(acac) show intensified emission at 520 nm, and higher efficiency; luminance of 47238 cd/m2, ηc -50.9 cd/A, ηp -49.3 lm w-1 and ηex

ur

-18.9 % at driving voltage of 3.0 V than [ITO: Ir(mnmpdi)2(acac) based device [L- 39326

Jo

cd/m2; ηc-46.0 cd/A; ηp -39.3 lm w-1; ηex -13.8 %; V-3.0]. The red device (620 nm) with SNSZO: Ir(mnpbi)2(acac) show luminance of 9058 cd/m2, ηc - 8.3 cd/A, ηp -6.4 lm w-1 and ηex -12.2 % at driving voltage 3.0 V than ITO: Ir(mnpbi)2(acac)device [L- 7632 cd/m2; ηc -4.1 cd/A; ηp -6.40 lm w-1; ηex -6.0 %; V-3.2 V]. The devices I, III and V show intensified emission than reference devices (II, IV& VI) since HIB is reduced by stabilizing EF by the embedded Ag NPs at glass: NSZO interface. Since the embedded Ag NPs at glass: NSZO

interface promotes holes to disperse across junction and enhanced efficiencies (ηc, ηp & ηex): leakage of holes all the way through emissive layer was decreased and make balanced h + - e recombination and thus the non-productive hole-current was removed. Because of larger area between emissive layer: HTL interface the charge injection is enhanced which results effective electron-hole recombination leads to enhanced device performances. Surfaceplasmon of metal NPS enhanced the emission intensity which can strongly promote the external emission of devices I, III and V. At SNSZO film, Ag NPs effectively excited such

ro of

emission and enhanced the device efficiencies (I, II and V). Efficient electroluminescent performances were harvested from the devices I, III and V using Ag NPs embedded at glass: NSZO interface. In CBP: Ir(ppy)3 (25 nm) based devices

-p

the carrier current decreases sharply since the carrier may undergo deep trapping at Ir(ppy)3 HOMO orbital. However, in CBP: Ir(fdbdi)3 (25 nm); CBP: Ir(mnmpdi)2(acac) (25 nm);

re

CBP: Ir(mnpbi)2(acac) (25 nm) based devices, the carrier current increased which may be

lP

attributed to the effect of direct injection into the dopant HOMO levels and the hopping transport through Ir(fdbdi)3/ Ir(mnmpdi)2(acac)/ Ir(mnpbi)2(acac) and dopant sites (Figure 7). Overall, the efficiencies of the RGB PhOLEDs indicate that the electroluminescent

na

efficiencies of devices based on different anodes are comparable and the electroluminescent performances of PHOLEDs with various anodes are displayed in Table 3 [83-89]. The

ur

efficiencies of SNSZO-based OLEDs were not inferior to other previously reported

Jo

efficiencies. This outstanding performance manifests the great potential of SNSZO film as an alternative anode for OLEDs. 4. Conclusion

Enhanced efficiencies have been obtained by incorporating Ag NPs at glass: SNSZO interface to avoid altering the hole mobility due to the coupling of surface plasmonic ability exerted by Ag NPs. Among the blue devices I (449 nm) and II (465 nm), blue device with

SNSZO: Ir(fdbdi)3 exhibit maximum luminance (L) of 42683 cd/m2, current efficiency (ηc) of 43.6 cd/A and power efficiency (ηp) of 45.3 lm W-1 and external quantum efficiency (ηex) of 20.2 % than ITO: Ir(fdbdi)3 based device [L- 35126 cd/m2; ηc - 38.4 cd/A; ηp - 37.3 lm w-1; ηex -15.1 %; V-3.2] at driving voltage 3.0 V. Similar observations were found for green and red devices. The green device with emissive layer SNSZO: Ir(mnmpdi)2(acac) show intensified emission at 520 nm and higher efficiency; luminance of 47238 cd/m2, ηc - 50.9 cd/A, ηp - 49.3 lm w-1

and ηex - 18.9 %

at driving voltage of 3.0 V than ITO:

ro of

Ir(mnmpdi)2(acac) based device [L- 39326 cd/m2; ηc-46.0 cd/A; ηp -39.3 lm w-1; ηex -13.8 %; V-3.0]. The red device (620 nm) with SNSZO: Ir(mnpbi)2(acac) show luminance of 9058 cd/m2, ηc - 8.3 cd/A, ηp -6.4 lm w-1 and ηex - 12.2 % at driving voltage 3.0 V than ITO:

-p

Ir(mnpbi)2(acac)device [L- 7632 cd/m2; ηc -4.1 cd/A; ηp -6.40 lm w-1; ηex -6.0 %; V-3.2 V]. The outcome of present investigation reveals the potential advantage by the use of SNSZO as

re

an alternative OLED anode in term of higher efficiency, low voltage and luminance. The

lP

superior characteristics of tailored silver embedded Ni-Ag-codoped ZnO anode points toward

na

the replacement of ITO anodes in future OLED applications.

Jo

ur

Conflict of interest: The authors declare no conflict of interest.

Acknowledgements This research was supported by the DST (Department of Science and Technology -

EMR/2014/000094, F.No. SR/S1/1C-73/2010, F.No. SR/S1/1C-07/2007), DRDO (Defence Research and Development Organization -213/MAT/10-11), CSIR (Council of Scientific and

Industrial Research -No. 01/ (2707)/13EMR-II), UGC (University Grant Commission -6-

Jo

ur

na

lP

re

-p

ro of

21/2008, F.No. 30-71/2004(SR)) and DST-Nano Mission (SR/NM/NS-1001/2016).

Reference [1] R. G. Gordon, Criteria for choosing transparent conductors, MRS Bull, 25 (2000) 52. https://doi.org/10.1557/mrs2000.151 [2] H. Liang and R. G. Gordon, Atmospheric pressure chemical vapour deposition of transparent conducting films of fluorine doped zinc oxide and their application to amorphous

silicon

solar

cells,

J.

Mater.

Sci.,

42

(2007)

6388.

https://doi.org/10.1007/s10853-006-1255-5

ro of

[3] J. Lee, T. H. Han, M. H. Park, D. Y. Jung, J. Seo, H. K. Seo, H. Cho, E. Kim, J. Chung, S. Y. Choi, T. S. Kim, T. W. Lee and S. Yoo, A uniform stable P-Type graphene doping method with the gold etching process, Nanotechnology, Nat. Commun., 7 (2016) 11791.

-p

https://doi.org/10.1038/ncomms11791

[4] H. M. Kim, D. Geng, J. Kim, E. H wang and J. Jang, Metal-oxide stacked electron

re

transport layer for highly efficient inverted quantum-dot light emitting diodes, ACS

lP

applied materials & interfaces, ACS Appl. Mater. Interfaces, 42 (2016) 28727. https://doi.org/10.1021/acsami.6b10314

[5] A. R. Madaria, A. Kumar and C. W. Zhou, Large scale, highly conductive and patterned

screens.

na

transparent films of silver nanowires on arbitrary substrates and their application in touch Nanotechnology,

22

(2011)

245201.

http://dx.doi.org/10.1088/0957-

ur

4484/22/24/245201

Jo

[6] J. Z. Song and H. B. Zeng, Transparent electrodes printed with nanocrystal inks for flexible

smart

devices,

Angew.Chem.

Int.

Ed.,

54

(2015)

9760.

https://doi.org/10.1002/anie.201501233

[7] V. Zardetto, T. M. Brown and A. Reale, Substrates for flexible electronics: A practical investigation on the electrical, film flexibility, optical, temperature, and solvent

resistance properties, J. Polym. Sci. Part B: Polym. Phys., 49 (2011) 638. https://doi.org/10.1002/polb.22227 [8] H. Tang, Y. Jiang, C. W. Tang and H. S. Kwok, Grid Optimization of Large-Area OLED Lighting

Panel

Electrodes.

J.

Disp.

Technol.,

12

(6)

(2016)

605-609.

https://doi.org/10.1109/JDT.2015.2511023 [9] J. Li, L. Hu, L. Wang, Y. Zhou, G. Gruner and T. J. Marks, Organic light-emitting diodes having

carbon

nanotube

anodes,

Nano

Lett.,

6

(11)

(2006)

2472-2477.

ro of

https://doi.org/10.1021/nl061616a [10] S. Ye, A. R. Rathmell, Z. Chen, I. E. Stewart and B. J. Wiley, Metal nanowire networks: the next generation of transparent conductors, Adv. Mater., 26 (2014) 6670.

-p

https://doi.org/10.1002/adma.201402710

[11] J. Wu, X. Que, Q. Hu, D. Luo, T. Liu, F. Liu, T. P. Russell, R. Zhu and Q. Gong, Multi-

re

Length Scaled Silver Nanowire Grid for Application in Efficient Organic Solar Cells.

lP

Adv. Funct. Mater., 26 (2016) 4822. https://doi.org/10.1002/adfm.201601049 [12] J. Z. Song, J. H. Li, J. Y. Xu and H. B. Zeng, Superstable transparent conductive Cu@ Cu4Ni nanowire elastomer composites against oxidation, bending, stretching, and

na

twisting for flexible and stretchable optoelectronics. Nano Lett., 14 (2014) 6298. https://doi.org/10.1021/nl502647k

ur

[13] J. Z. Song, S. A. Kulinich, J. H. Li, Y. L. Liu and H. B. Zeng, A General One Pot

Jo

Strategy for the Synthesis of High Performance Transparent Conducting Oxide Nanocrystal Inks for All Solution Processed Devices, Angew. Chem., 127 (2015) 472. https://doi.org/10.1002/ange.201408621

[14] M. Vosgueritchian, D. J. Lipomi and Z. Bao, Highly conductive and transparent PEDOT: PSS films with a fluorosurfactant for stretchable and flexible transparent electrode, Adv. Funct. Mater., 22 (2012) 421. https://doi.org/10.1002/adfm.201101775

[15] Y. W. Li, L. Mao, Y. L. Gao, P. Zhang, C. Li, C. Q. Ma, Y. F. Tu, Z. Cui and L. W. Chen, ITO-free photovoltaic cell utilizing a high-resolution silver grid current collecting layer. Solar Energy Materials and Solar Cells Sol. Energy Mater. Sol. Cells., 113 (2013) 85. https://doi.org/10.1016/j.solmat.2013.01.043 [16] L. Mao, Q. Chen, Y. W. Li, Y. Li, J. H. Cai, W. M. Su, S. Bai, Y. Z. Jin, C. Q. Ma, Z. Cui and L. W. Chen, Flexible silver grid/PEDOT: PSS hybrid electrodes for large area inverted

polymer

solar

cells,

Nano

Energy,

10

(2014)

ro of

259.https://doi.org/10.1016/j.nanoen.2014.09.007 [17] H. Lee, I. Park, J. Kwak, D. Y. Yoon and C. Lee, Improvement of electron injection in inverted bottom-emission blue phosphorescent organic light emitting diodes using zinc nanoparticles,

Appl.

Phys.

Lett.,

96

(2010)

153306.

-p

oxide

https://doi.org/10.1063/1.3400224

re

[18] J. Kang, Y. Jang, Y. Kim, S. H. Cho, J. Suhr, B. H. Hong, J. B. J. Choi and D. Byun, An

lP

Ag-grid/graphene hybrid structure for large-scale, transparent, flexible heaters. Nanoscale, 7 (2015) 6567. DOI:10.1039/C4NR06984F [19] P. K. Nayak, J. Yang, J. Kim, S. Chung, J. Jeong, C. Lee and Y. Hong, Spin-coated Ga-

na

doped ZnO transparent conducting thin films for organic light-emitting diodes, J. Phys. D: Appl. Phys., 42 (2008) 035102. doi:10.1088/0022-3727/42/13/139801

ur

[20] H. Kim, J. S. Horwitz, W. H. Kim, S. B. Qadri and Z. H. Kafafi, Anode material based

Jo

on Zr-doped ZnO thin films for organic light-emitting diodes, Appl. Phys. Lett., 83 (2003) 3809. https://doi.org/10.1063/1.1623933

[21] X. Jiang, F. L. Wong, M. K. Fung and S. T. Lee, Aluminum-doped zinc oxide films as transparent conductive electrode for organic light-emitting devices, Appl. Phys. Lett., 83 (2003) 1875. https://doi.org/10.1063/1.1605805

[22] J. Jayabharathi, A. Prabhakaran, V. Thanikachalam and M. Sundharesan, Hybrid organic-inorganic light emitting diodes: Effect of Ag-doped ZnO. J. Photochem. Photobiol. A, 325 (2016) 88. https://doi.org/10.1016/j.jphotochem.2016.04.007 [23] T. Kim, H. Kang, S. Jeong, D. J. Kang, C. Lee, C. H. Lee, M. K. Seo, J. Y. Lee and B. J. Kim, Plasmonic nanostructures for organic photovoltaic devices., Appl. Mater. Interfaces, 6 (2014) 16956. http://dx.doi.org/10.1088/2040-8978/18/3/033001 [24] J. Meyer, S. Hamwi, T. Bülow, H. H. Johannes, T. Riedl and W. Kowalsky, Highly

ro of

efficient simplified organic light emitting diodes, Appl. Phys. Lett., 91 (2007) 113506. https://doi.org/10.1063/1.2784176

[25] Z. Su, L. Wang, Y. Li, G. Zhang, H. Zhao, H. Yang, Y. Ma, B. Chu and W. Li, Surface

-p

plasmon enhanced organic solar cells with a MoO3 buffer layer, Appl. Mater. Interfaces, 5 (2013) 12847. https://doi.org/10.1021/am404441n

re

[26] S. Shi, V. Sadhu, R. Moubah, G. Schmerber, Q. Bao and S. R. P. Silva, Solution-

lP

processable graphene oxide as an efficient hole injection layer for high luminance organic light-emitting diodes, J. Mater. Chem. C, 1 (2013) 1708. DOI:10.1039/C3TC00707C [27] S. Liu, F. Meng, W. Xie, Z. Zhang, L. Shen, C. Liu, Y. He, W. Guo and S. Ruan, Highly

na

efficient ITO-free polymer solar cells based on metal resonant microcavity using WO3/Au/WO3 as transparent electrodes, Appl. Phys. Lett., 103 (2013) 233303.

ur

https://doi.org/10.1016/j.orgel.2014.04.026

Jo

[28] J. H. Lee, J. H. Park, J. S. Kim, D. Y. Lee and K. Cho, High efficiency polymer solar cells with wet deposited plasmonic gold nanodots. Org. Electron., 10

(2009) 416.

https://doi.org/10.1016/j.orgel.2009.01.004

[29] H. Choi, J. P. Lee, S. J. Ko, J. W. Jung, H. Park, S. Yoo, O. Park, J. R. Jeong, S. Park and J. Y. Kim, Multipositional silica-coated silver nanoparticles for high-performance polymer solar cells, Nano. Lett., 13 (2013) 2204. https://doi.org/10.1021/nl400730z

[30] A. Kumar, R. Srivastava, D. S. Mehta and M. N. Kamalasanan, Efficiency enhancement of organic light emitting diode via surface energy transfer between exciton and surface Plasmon, Org.Electron.,13 (2012) 1750. https://doi.org/10.1016/j.orgel.2011.10.008 [31] Y. Zhou, Y. Yuan, J. Lian, J. Zhang, H. Pang, L. Cao and X. Zhou, Mild oxygen plasma treated PEDOT: PSS as anode buffer layer for vacuum deposited organic light-emitting diodes, Chem. Phys. Lett., 427 (2006) 394. https://doi.org/10.1016/j.cplett.2006.06.035 [32] D. Wang, K. Yasui, M. Ozawa, K. Odoi, S. Shimamura and K. Fujita, Effects of gold-

ro of

nanoparticle surface and vertical coverage by conducting polymer between indium tin oxide and the hole transport layer on organic light-emitting diodes, Appl. Phys. Lett., 102 (2013) 023302. https://doi.org/10.1021/acsami.5b04248

-p

[33] J. M. Moon, J. H. Bae, J. A. Jeong, S. W. Jeong, N. J. Park, H. K. Kim, J. W. Kang, J. J. Kim, and M. S. Yi, Enhancement of hole injection using ozone treated Ag nanodots

re

dispersed on indium tin oxide anode for organic light emitting diodes, Appl. Phys. Lett.,

lP

90 (16) (2007) 163516-3. https://doi.org/10.1063/1.2719153 [34] I. M. Chan, W. C. Cheng, and F. C. Hong, Enhanced performance of organic lightemitting devices by atmospheric plasma treatment of indium tin oxide surfaces, Appl.

na

Phys. Lett., 80 (2002) 13. https://doi.org/10.1063/1.1428624 [35] C. C. Wu, I. Wu, J. C. Sturn and A. Kahn, Surface modification of indium tin oxide by

ur

plasma treatment: An effective method to improve the efficiency, brightness, and

Jo

reliability of organic light emitting devices, Appl. Phys. Lett., 70 (1997) 1348. https://doi.org/10.1063/1.118575

[36] F. Li, H. Tang, J. Shinar, O. Resto, and S. Z. Weisz, Effects of aquaregia treatment of indium–tin–oxide substrates on the behavior of double layered organic light-emitting diodes, Appl. Phys. Lett., 70 (1997) 2741. https://doi.org/10.1063/1.119008

[37] C. Ganzorig, K. J. Kwak, K. Yagi and M. Fujihira, Fine tuning work function of indium tin oxide by surface molecular design: Enhanced hole injection in organic electroluminescentdevices, Appl. Phys.Lett.,79(2001)272. https://doi.org/10.1063/1.1384896 [38] S. F. J. Appleyard and M. R. Willis, Electroluminescence: enhanced injection using ITO electrodes coated with a self assembled monolayer, Opt. Mater., 9 (1998) 120. https://doi.org/10.1016/S0925-3467(97)00110-9 [39] C. M. Hsu and W. T. Wu, Improved characteristics of organic light-emitting devices by

ro of

surface modification of nickel-doped indium tin oxide anode. Appl. Phys. Lett., 85 (2004) 840. https://doi.org/10.1063/1.1777416

[40] C. M. Hsu, J. W. Lee, T. H. Meen, and W. T. Wu, Preparation and characterization of

-p

Ni–indium tin oxide cosputtered thin films for organic light-emitting diode application, Thin Solid Films, 474 (2005) 19. https://doi.org/10.1016/j.tsf.2004.08.005

re

[41] I. M. Chan, T. Y. Hsu, and F. C. Hong, Enhanced hole injections in organic light-

lP

emitting devices by depositing nickel oxide on indium tin oxide anode, Appl. Phys. Lett., 81 (2002) 1899. https://doi.org/10.1016/j.tsf.2004.08.005 [42] H. Sato, T. Minami, S. Takata, and T. Yamada, Transparent conducting p-type NiO thin

na

films prepared by magnetron sputtering ,Thin Solid Films, 236 (1993) 27. https://doi.org/10.1016/0040-6090(93)90636-4

ur

[43] J. H. Bae, J. M. Moon, J. W. Kang, H. D. Park, J. J. Kim, W. J. Cho, and H. K. Kim,

Jo

Transparent low resistance, and flexible amorphous ZnO-doped In2O3 anode grown on a PES substrate, J. Electrochem. Soc., 154 (2007) J81. doi: 10.1149/1.2426800

[44] (a) M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M.

Ishida, T.Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.

Dannenberg, V. G. Zakrzewski, S.

Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.

ro of

Martin, D. J. Fox, T. Keith, M. A. A. Laham, C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonzalez and J. A. Pople, Gaussian 09 (Revision A.02). Gaussian, Inc., Wallingford, CT, 2009. (b) T. Lu

-p

and F. Chen, J. Comput. Chem., 33 (2012) 580-592.

[45] R. V. Rao and P. R. Kiran, Green synthesis approach on the anti-bacterial credentials

re

and characterization of silver nanoparticle-coated leafy extracts of Mimusops elengi,

[46]

M.

Nonoyama,

lP

Nano Science and Nano Technology, 6 (2012) 28. doi: 10.1016/j.colsurfb.2013.03.017. Benzo

[h]

quinolin-10-yl-N

Iridium

(III)

Complexes,

Bull.Chem.Soc.Jpn., 47 (1974) 767. https://doi.org/10.1246/bcsj.47.767

na

[47] R. Georgekutty, M. K. Seery and S. C. Pillai, A highly efficient Ag-ZnO photocatalyst: synthesis, properties, and mechanism, J. Phys. Chem. C, 112 (2008) 13563.

ur

https://doi.org/10.1021/jp802729a

Jo

[48] C. Chen, Y. Zheng, Y. Zhan, X. Lin, Q. Zheng and K. Wei, Enhanced Raman scattering and photocatalytic activity of Ag/ZnO heterojunction nanocrystals, Dalton Trans., 40 (2011) 9566. DOI:10.1039/C1DT10799B

[49] M. M. Khan, S. A. A. Ansari, J. Lee, M. H. Cho, Highly visible light active Ag@TiO2 nanocomposites synthesized using an electrochemically active biofilm: a novel biogenic approach, Nanoscale, 5 (2013) 4427. DOI:10.1039/C3NR00613A

[50] S. Rakshit, S. Ghosh, S. Chall, S. S. Mati, S.P. Moulik and S.C. Bhattacharya, Controlled synthesis of spin glass nickel oxide nanoparticles and evaluation of their potential antimicrobial activity: A cost effective and eco friendly approach, RSC Adv., 3 (2013) 19348. DOI:10.1039/C3RA42628A [51] R. J. V. Michael, B. Sambandam, T. Muthukumar, M. J. Umapathya and P.T. Manoharan, Spectroscopic dimensions of silver nanoparticles and clusters in ZnO matrix and their role in bioinspired antifouling and photocatalysis, Phys. Chem. Chem. Phys., 16

ro of

(2014) 8541. DOI:10.1039/C4CP00169A [52] Y. Zhu, H. Guo, Y. Wu, C. C. S. Tao and Z. Wu, Surface-enabled superior lithium storage of high-quality ultrathin NiO nanosheets, J. Mater. Chem. A, 2 (2014) 7904.

-p

DOI:10.1039/C4TA00257A

[53] R. O. Moussodia, L. Balan, C. Merlin, C. Mustind and R. Schneider, Biocompatible and

re

stable ZnO quantum dots generated by functionalization with siloxane-core PAMAM

lP

dendrons, J. Mater. Chem., 20 (2010) 1147. DOI:10.1039/B917629B [54] W. H. Eisa, Y. K. A. Moneam, Y. Shaaban, A. A. A. Fattah and A. M. A. Zeid, Gammairradiation assisted seeded growth of Ag nanoparticles with in PVA matrix, Mater.

na

Chem. Phys., 128 (2011) 109. https://doi.org/10.1016/j.matchemphys.2011.02.076 [55] J. Jayabharathi, G. Abirama Sundari, V. Thanikachalam, P. Jeeva and S. Panimozhi, A

ur

dodecanethiol-functionalized Ag nanoparticle-modified ITO anode for efficient

Jo

performance of organic light-emitting devices, RSC Adv., 7 (2017) 38923. DOI: 10.1039/C7RA07080B

[56] A. Kumar, R. Srivastava, D. S. Mehta and M. N. Kamalasanan, Surface plasmon enhanced blue organic light emitting diode with nearly 100% fluorescence efficiency, Org. Electron, 13 (2012) 1750. https://doi.org/10.1016/j.orgel.2011.10.008

[57] J. Jayabharathi, E. Sarojpurani, V. Thanikachalam, and P. Jeeva, "Interfacial chargetransfer process in nanosemiconductor-N-benzylpiperidine phenanthroimidazole (BDPI)metal heterostructure: A combined experimental and theoretical studies of BDPI-(FeO) n composites,

J.Photochem.

Photobiol.A,

342

(2017)

59.

https://doi.org/10.1016/j.jphotochem.2017.04.001 [58] Q. Deng, X. Duan, H. L. Dickon, H. Tang, Y. Yang, and M. Kong, Ag nanoparticle decorated nanoporous ZnO microrods and their enhanced photocatalytic activities, ACS

ro of

Appl. Mater. Interfaces, 4 (2012) 6030-6037. https://doi.org/10.1021/am301682g [59] R. Saravanan, N. Karthikeyan, V. K. Gupta, E. Thirumal, P. Thangadurai, and V. Narayanan, ZnO/Ag nanocomposite: an efficient catalyst for degradation studies of

https://doi.org/10.1016/j.msec.2013.01.046

-p

textile effluents under visible light, Mater. Sci. Eng, C, 33 (2013) 2235.

re

[60] S. A. Ansari, M. M. Khan, M. O. Ansari, J. Lee and M. H. Cho, Biogenic synthesis,

lP

photocatalytic, and photoelectrochemical performance of Ag–ZnO nanocomposite, J. Phys. Chem. C, 117 (2013) 27023. https://doi.org/10.1021/jp410063p [61] Y. Zheng, C. Chen, Y. Zhan, X. Lin, Q. Zheng, K. Wei and J. Zhu, Photocatalytic

na

activity of Ag/ZnO heterostructure nanocatalyst: correlation between structure and property, J. Phys. Chem., C, 112 (2008) 10773. https://doi.org/10.1021/jp8027275

ur

[62] B. Pala, D. Sarkara and P. K. Giri, Structural, optical, and magnetic properties of Ni

Jo

doped ZnO nanoparticles: Correlation of magnetic moment with defect density, Applied Surface Science, 35 (2015) 804. https://doi.org/10.1016/j.apsusc.2015.08.163

[63] J. Jayabharathi, E. Sarojpurani, V. Thanikachalam, and P. Jeeva, Far-Field Enhancement by Silver Nanoparticles in Organic Light Emitting Diodes Based on Donor− π–Acceptor Chromophore,

Ind.

Eng.

Chem.

https://doi.org/10.1021/acs.iecr.7b00783

Res.,

56

(2017)

5325.

[64] J. Becker, K. R. Raghupathi, J. St. Pierre, D. Zhao and R. T. Koodali, Tuning of the crystallite and particle sizes of ZnO nanocrystalline materials in solvothermal synthesis and their photocatalytic activity for dye degradation, J. Phys. Chem. C, 115 (2011) 13844. https://doi.org/10.1021/jp2038653 [65] O. Lupan, T. Pauporté, T.nL. Bahers, B. Viana and I. Ciofini, Wavelength-emission tuning of ZnO nanowire-based light-emitting diodes by Cu doping: experimental and computational

insights,

Adv.

Funct.

Mater.,

18

(2011)

3564.

ro of

https://doi.org/10.1002/adfm.201100258 [66] T. Pauporté, O. Lupan, J. Zhang, T. Tugsuz, I. Ciofini, F. Labat and B. Viana, Lowtemperature preparation of Ag -doped ZnO nanowire arrays, DFT study,

-p

and application to light-emitting diode, ACS Appl. Mater. Interfaces, 2015, 7, 11871. https://doi.org/10.1021/acsami.5b01496

re

[67] A. Echresh, C. O. Chey, M. Z. Shoushtari, O. Nur, M. Willander, Tuning the emission of

lP

ZnO nanorods based light emitting diodes using Ag doping, J. Appl. Phys., 116 (2014) 193104. https://doi.org/10.1063/1.4902526

[68] X. L. Zhang, J. L. Zhao, S. G. Wang, H. T. Dai and X. W. Sun, Materials, Devices, and for

Solid

State

na

Applications

Lighting

XVII,

N,

4

(2013)

86411.

https://doi.org/10.1016/j.jphotochem.2016.04.007

ur

[69] J. Jayabharathi, V. Thanikachalam, K. Saravanan and N. Srinivasan, Iridium (III)

Jo

complexes with orthometalated phenylimidazole ligands subtle turning of emission to the saturated green colour, J. Fluoresc., 21 (2011) 507 . DOI https://doi.org/10.1007/s10895010-0737-7

[70] K. Saravanan, N. Srinivasan, V. Thanikachalam and J. Jayabharathi, Synthesis and photophysics of some novel imidazole derivatives used as sensitive fluorescent

chemisensors, J. Fluoresc., 21 (2011) 65. DOI https://doi.org/10.1007/s10895-010-06905 [71] J. Jayabharathi, V. Thanikachalam, N. Srinivasan and K. Saravanan, Validation of a method for the analysis of nine quinolones in eggs by pressurized liquid extraction and liquid chromatography with fluorescence detection, J. Fluoresc., 21 (2011) 596. https://doi.org/10.1016/j.talanta.2011.04.021 [72] J. Jayabharathi, V. Thanikachalam and K. Saravanan, Effect of substituents on the

photophysical

properties,

J.

Photochem.

ro of

photoluminescence performance of Ir (III) complexes: Synthesis, electrochemistry and Photobiol.

https://doi.org/10.1016/j.jphotochem.2009.07.027

A,

208

(2009)

13.

-p

[73] S. Lamansky, P. Djurovich, D. Murphy, F. Abdel Razzaq, H. F. Lee, C. Adachi, P. E. Burrows, S. R. Forrest and M. E. Thompson, Highly phosphorescent bis-cyclometalated

re

iridium complexes: synthesis, photophysical characterization, and use in organic light

lP

emitting diodes, J. Am. Chem. Soc., 123 (2001) 4304. DOI: 10.1021/ja003693s [74] M. G. Colombo, A. Hauser and H. U. Gudel, Evidence for strong mixing between the LC and MLCT excited states in bis (2-phenylpyridinato-C2, N')(2, 2'-bipyridine) iridium

na

(III), Inorg. Chem., 32 (1993) 3088. https://doi.org/10.1021/ic00066a020 [75] A. Ortiz, J. C. Alonso and E. H. Poniatowski, Spray deposition and characterization of thin

ur

zirconium-oxide

films,

J.

Electr.

Mater.,

34

(2006)

150.

Jo

http://dx.doi.org/10.1007/s11664-005-0226-y [76] B. X. Mi, P. F. Wang, M. W. Liu, H. L. Kwong, N. B. Wong, C. S. Lee and S. T. Lee, Thermally stable hole-transporting material for organic light-emitting diode: An isoindole derivative, Chem. Mater., 15 (2003) 3148 . https://doi.org/10.1021/cm030292d [77] J. D. Priest, G. Y. Zheng, N. Goswami, D. M. Eichhorn, C. Woods and D. P. Rillema, Structure, physical, and photophysical properties of platinum (II) complexes containing

bi dentate aromatic and bis (diphenylphosphino) methane as ligands, Inorg. Chem., 39 (2000) 1955. https://doi.org/10.1021/ic991306d [78] C. H. Chang, W. S. Liu, S. Y. Wu, J. L. Huang, C. Y. Hung, Y. L. Chang, Y. C. Wu, W. C. Chen and Y. C. Wu, Ga-doped Ti ZnO transparent conductive oxide used as an alternative

anode

in

blue,

green,

and

red

phosphorescent

OLEDs.

Phys.Chem.Chem.Phys., 16 (2014) 19618. doi: 10.1039/c4cp02924k. [79] J. Jayabharathi, V. Thanikachalam and K. Saravanan, Effect of substituents on the

photophysical

properties,

J.

Photochem.

ro of

photoluminescence performance of Ir (III) complexes: Synthesis, electrochemistry and Photobiol.

http://dx.doi.org/10.1016/j.jphotochem.2009.07.027

A,

208

(2009)

13.

-p

[80] J. Jayabharathi, G. Abirama Sundari, V.Thanikachalam and S. Panimozhi, Enhanced internal quantum efficiency of organic light-emitting diodes: A synergistic effect, J. Photobiol.

A,

364

re

Photochem.

(2018)

577.

lP

https://doi.org/10.1016/j.jphotochem.2018.06.041

[81] X. Y. Wu, L. L. Liu, W. C. H. Choy, T. C. Yu, P. Cai, Y. J. Gu, Z. Q. Xie, Y. N. Zhang, L. Y. Du, Y. Q. Mo, S. P. Xu and Y. G. Ma, Substantial performance improvement in

na

inverted polymer light-emitting diodes via surface plasmon resonance induced electrode quenching control, Appl. Mater. Interfaces, 6 (2014) 11001 . doi: 10.1021/am5033764.

ur

[82] C. H. Chang, C. L. Ho, Y. S. Chang, I. C. Lien, C. H. Lin, Y. W. Yang, J. L. Liao and Y.

Jo

Chi, Blue-emitting Ir (III) phosphors with 2-pyridyl triazolate chromophores and fabrication of sky blue-and white-emitting OLEDs, J. Mater. Chem. C, 1 (2013) 2639. DOI:10.1039/C3TC00919J

[83] H. Kim, J. S. Horwitz, W. H. Kim, S. B. Qadri and Z. H. Kafa, Anode material based on Zr-doped ZnO thin films for organic light-emitting diodes, Appl. Phys. Lett., 2003, 83, 3809. http://dx.doi.org/10.1063/1.1623933

[84] J. W. Kang, W. I. Jeong, J. J. Kim, H. K. Kim, D. G. Kim and G. H. Lee, Highperformance flexible organic light-emitting diodes using amorphous indium zinc oxide anode, Electrochem. Solid-State Lett., 2007, 10, J75. doi: 10.1149/1.2720635 [85] L. Wang, J. S. Swensen, E. Polikarpov, D. W. Matson, C. C. Bonham, W. Bennett, D. J. Gaspar and A. B. Padmaperuma, Highly efficient blue organic light-emitting devices with indium-free transparent anode on flexible substrates, Org. Electron., 11 (2010) 1555-1560. https://doi.org/10.1016/j.orgel.2010.06.018

ro of

[86] H. Lee, I. Park, J. Kwak, D. Y. Yoon and C. Lee, Improvement of electron injection in inverted bottom-emission blue phosphorescent organic light emitting diodes using zinc oxide

nanoparticles,

Appl.

Phys.

Lett.,

96

153306–153313.

-p

https://doi.org/10.1063/1.3400224s

(2010)

[87] C. H. Chang, W. S. Liu, S. Y. Wu, J. L. Huang, C. Y. Hung, Y. L. Chang, Y. C. Wu, W.

re

C. Chen and Y. C. Wu, Ga-doped TiZnO transparent conductive oxide used as an

lP

alternative anode in blue, green, and red phosphorescent OLEDs, Phys. Chem. Chem. Phys., 16 (2014) 19618. DOI:10.1039/C4CP02924K [88] J. Jayabharathi, E. Sarojpurani, V. Thanikachalam and P. Jeeva, Ga-Ti-codoped ZnO

Photochem.

na

embedded silver nanoparticles as an alternative anode in blue and green OLEDs, J. Photobiol.

A:

Chemistry,

356,

(2018)

290.

ur

https://doi.org/10.1016/j.jphotochem.2017.12.035

Jo

[89] J. Jayabharathi, P. Nethaji and V. Thanikachalam, Promotional effect of silver nanoparticle embedded Ga–Zr-codoped TiO2 as an alternative anode for efficient blue, green and red PHOLEDs, RSC Adv., 9 (2019) 13664. DOI:10.1039/C9RA01025D

Jo

ur

na

lP

re

-p

ro of

Figure 1. X-ray diffraction of NSZO (JCPDS: 65-3411) and Ag NPs (JCPDS: 87-0597).

Figure 2. HR-TEM images, [inset: histogram] and SAED pattern of (a) NSZO, (b) Ag NPs

Jo

ur

na

lP

re

-p

ro of

and EDX spectrum of NSZO (c) Ag NPs (d).

Jo

ur

na

lP

re

-p

ro of

Figure 3. X-ray photoelectron spectra of NSZO.

Figure 4. DRS spectra of ZnO, NSZO and Ag NPs (a), F(R)hv)2 Vs hv (eV): direct (b), F(R)hv)0.5Vs hv (eV): indirect (c), PL spectra of ZnO, Ag and NSZO (d) and (e)

Jo

ur

na

lP

re

-p

ro of

Fermi energy level of silver metal and energy level of ZnO.

Figure 5. (a) ORTEP of 2-(1-methoxynaphthalen-4-yl)-1-(4-methoxyphenyl)-4,5-diphenyl1H-imidazole (mnmpdi), (b) Optimized geometry, HOMO and LUMO of

Jo

ur

na

lP

re

-p

ro of

Ir(fdbdi)3, Ir(mnpbi)2(acac) and Ir(mnmpdi)2(acac).

Jo

ur

na

lP

re

-p

ro of

Figure 6. Normalized absorption (a), emission spectra (b), Life time spectra (c), Cyclic voltamogram (d) and TGA graph (e) of Ir(fdbdi)3, Ir(mnpbi)2(acac) and Ir(mnmpdi)2(acac).

Jo

ur

na

lP

re

-p

ro of

Figure 7. (a) Fabricated device structure, (b) (i) carrier trapping at CBP:Ir(ppy)3 and (ii) carrier hopping through CBP:Ir(fdbdi)3/ Ir(mnpbi)2 (acac) / Ir(mnmpdi)2(acac), (c) energy level diagram of ITO/ NPB / CBP:Ir(fdbdi)3 or CBP: Ir(mnpbi)2(acac) or CBP: Ir(mnmpdi)2(acac) /LiF/ Al and (d) RGB light emission.

Jo

ur

na

lP

re

-p

ro of

Figure 8. Electroluminescence performances: (a) Luminance versus Voltage; (b) External quantum efficiency versus Current density; (c) Current efficiency versus Current density, (d) Power efficiency versus Current density and (e) EL spectra of Ir(fdbdi)3, Ir(mnpbi)2(acac) and Ir(mnmpdi)2(acac).

Jo

ur

na

lP

re

-p

ro of

Scheme 1. Synthetic route of Ir(fdbdi)3, Ir(mnpbi)2(acac) and Ir(mnmpdi)2(acac).

Table 1: Optical and thermal properties of Ir(fdbdi)3, Ir(mnmpdi)2 (acac) and Ir(mnpbi)2(acac) Parameters

Ir(fdbdi)3

Ir(mnmpdi)2 (acac) Ir(mnpbi)2 (acac)

262,340,390

252,363,381

280,318,402

λem(nm)

440,446

510,526

615,620

Td (°C)

423

430

452

ϕ

0.95

0.79

0.70

-5.38/-2.20

-5.10/-2.30

-5.12/-2.78

-3.18

2.87

-2.34

1.6

2.9

2.0

7.0

3.0

3.7

0.9

0.7

1.8

HOMO/LUMO(eV) Eg (eV) τ (ns) kr x 108 (s-1) 8

-1

Jo

ur

na

lP

re

-p

knr x 10 (s )

ro of

λab(nm)

43

Table 2: Comparative device efficiencies of Ag/ Ni-Ag-ZnO and ITO RGB PHOLEDs. Devices

Von

a

L

ɳxe

b

c

ɳc

e

ɳp

f

Zɳp

g

Zɳex

h

Zɳc

i

ZɳL

CIE

EL

(V)

(cd/m2)

)%(

(cd A-1)

(lm W-1)

(%)

(%)

(%)

(%)

(x, y)

(nm)

Ir(fbdi)3 :ITO

3.2

35126

15.1

38.4

37.3

--

--

--

--

0.16,0.10

465

Ir(fbdi)3 :SNSZOd

3.0

42683

20.2

43.6

45.3

21.5

33.8

13.5

21.4

0.15,0.10

449

Ir(mnmpdi) 2:ITO

3.2

39326

13.8

46.0

39.3

--

--

--

--

0.12,0.33

530

Ir(mnmpdi)2 :SNSZOd

3.0

47238

18.9

50.9

49.3

20.1

37.0

10.7

25.4

0.12,0.32

520

Ir(mpbi)2acac :ITO

3.2

7632

6.0

4.1

3.9

--

--

--

--

0.68,0.32

630

Ir(mpbi)2acac:SNSZOd

3.0

9058

12.1

8.3

6.4

18.7

101.7

102.4

64.1

0.68,0.30

620

L – Brightness; bηex – maximum external quantum efficiency; cηc - Luminous efficiency; eηp -Power efficiency; fZηp = [ηpd- ηp /ηp] x100, ηpd – maximum power efficiency with NPs; ηp – maximum power efficiency without NPs; gZηex = [ηexd- ηex /ηex] x100, ηexd – maximum external quantum efficiency with NPs; ηex – maximum external quantum efficiency without NPs; , ηcd – maximum luminous efficiency with NPs; ηc – maximum luminous efficiency without NPs: iZL = ]Ld-L/L] x100, hZηc = [ηcd- ηc/ηc] x100, Ld – maximum brightness with NPs; L – maximum brightness without NPs,

Jo

ur

na

lP

re

-p

ro of

a

44

Emissive materials /color

Zr:ZnO

Alq3/green

0.87

-

79

In:ZnO

Fac-Ir(ppy)3/green

13.2

30.7

80

13.7

32.7

80

8.5

14.1

80

12.4

30.1

80

15.2

31.6

81

16.6

33.1

81

16.3

33.7

81

FIrpic/blue

8.2

-

82

FIrpic/blue

19.0

-

82

Ir(piq)2acac/red

9.1

-

83

Fac-Ir(ppy)3/green

14.5

-

83

Ir(bpima)2 (pic)/blue

19.2

-

84

Ir(fpi)3/green

15.6

-

84

Ir(fni)3/blue

19.4

-

85

Ir(tfpdni)2 (pic)/green

17.5

-

85

Ir(bbt)2 (acac)/red

9.3

-

85

20.2

45.3

This work

Ir(mnmpdi)2 (acac)/green

18.9

49.3

This work

Ir(mpbi)2 (acac)/red

12.1

6.4

This work

FIrpic/blue

NPs

Ga-Ti-ZnO

Ag/Ga-Ti-ZnO

Ag/Ga-Zr-TiO2

Jo

ur

na

lP

Ag/Ni-Ag-ZnO Ir(fdbdi)3/blue

re

Ga:ZnO

EQE (%) PE(lm/W) Reference

ro of

Anode

-p

Table 3: External quantum efficiency of OLEDs with various anodes.