- Email: [email protected]
Probing the energy transfer process by controlling the morphology of CH3NH3PbBr3 nanocrystals with rhodamine B dye
Journal of Luminescence 215 (2019) 116609
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Probing the energy transfer process by controlling the morphology of CH3NH3PbBr3 nanocrystals with rhodamine B dye
T
Parul Bansal, Prasenjit Kar∗ Department of Chemistry, Indian Institute of Technology (IIT), Roorkee, Haridwar, Uttarakhand, 247667, India
A R T I C LE I N FO
A B S T R A C T
Keywords: Nanostructures Photoluminescence FRET Morphology Rhodamine B
A facile synthesis of tunable blue to green luminescent colloidal MAPbBr3 Perovskite NCs is synthesized by solution processed ligand assisted re-precipitation technique (LARP). Different behaviour in optical properties and morphology of MAPbBr3 perovskite NCs has been observed by tuning the ratio of oleic acid and oleylamine. Rhodamine B has been chosen as dye to study electron migration between perovskite NCs and dye. It has been investigated that both blue and green luminescent nanoparticles leads to different energy transfer behaviour with dye. Green luminescent MAPbBr3 nanoparticles are able to show Förster Resonance Energy Transfer whereas in blue luminescent nanoparticles, there is fluorescence quenching because of aggregation between perovskite and rhodamine b dye. These studies have been utilized in study of different interaction between tunable perovskite and rhodamine B dye.
1. Introduction The expectation of low cost clean energy has led to deviation towards research of new materials and processes to achieve strategies for light harvesting in photovoltaics [1–3]. Earlier a lot of investigations have been performed using semiconductor quantum dots (QDs) which possess tunability in band gap and makes ideal candidates as light harvesters in quantum dot solar cells (QDSCs) [3–5]. Recently organometal halide perovskites have exhibited a prodigious potential not only in LED devices but also photovoltaic applications [6–8]. The earliest studies on perovskites have been done in 70s but perovskite nanocrystals (NCs) attract the interest of the scientific community in recent years. These nanoparticles are having various applications in photovoltaic solar cells, sensors, light emitting diodes, lasers, photodetectors [6–14]. Perovskite nanocrystals are particularly ensembled for such applications due to their high absorption cross-section, narrow emission band, high quantum yield and recently, used as donors in nanocrystal–dye FRET couple [8–14,26]. However, instability and sensitivity of these materials towards moisture leads to difficulty in confining their applications [10]. The first solution based colloidal MAPbBr3 NCs was reported by Pérez -Prieto et al.6. The absorption and PL peaks of these nanocrystalline materials were reported as 527 nm and 530 nm respectively with the PLQY value of 20%. Later, Tyagi et al. have revealed the blue shift in absorption peak of MAPbBr3 with respect to bulk MAPbBr3 and
∗
introduced the concept of quantum confinement in size of MAPbBr3 nanocrystals [15]. A lot of studies have been performed on ligand, temperature, concentration, time dependent tunability in optical studies and morphology of nanoparticles [14–20] but a lot of studies are still under exploration. Energy transfer is the unique concept introduced from photosynthesis. It is a process where an excited donor interacts with a relaxed acceptor, resulting in a relaxed donor and excited acceptor [21,22]. Generally they follow nonradiative pathways including Förster Resonance Energy Transfer, Dexter Energy Transfer, collisional quenching and exciplex state [21–24]. Energy transfer studies between quantum dot-quantum dot, quantum dot - dye and other systems have been probed in conventional semiconductor quantum dots such as CdS, CdSe etc through Van der waals interactions and other supramolecular systems [21–25]. Till now hybrid perovskite nanocrystals have been explored mostly as light emitting diodes [8–10]. These perovskite materials have more challenging properties as compared to conventional semiconductors and equally serve as light harvesting materials. Muthu et al. were the one who reported light harvesting antenna properties of hybrid perovskites with different dyes through FRET mechanism [26]. These energy and electron transfer processes are very important for advanced optoelectronic devices [27–29]. Hybrid perovskites are having two unique properties: intense absorption in visible range and excellent photoluminescence with high quantum yield which makes them superior applicants for energy
Corresponding author E-mail addresses: [email protected], [email protected] (P. Kar).
https://doi.org/10.1016/j.jlumin.2019.116609 Received 21 February 2019; Received in revised form 30 June 2019; Accepted 5 July 2019 Available online 06 July 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
Journal of Luminescence 215 (2019) 116609
P. Bansal and P. Kar
Scheme 1. Schematic illustration of Different energy transfer behaviour of MAPbBr3 perovskite NCs with rhodamine dye.
antisolvent [10] while in this report all the experiments were carried out in dry chloroform. By changing the concentration of capping ligands, oleic acid and oleylamine as 100 μl and 200 μl, we had obtained blue luminescent quantum dots of MAPbBr3 (Scheme 1). Whereas keeping oleic acid as 200 μl and oleylamine as 32 μl had lead to formation of green luminescent perovskite solution.
transfer and storage purposes [6,10,18]. In this report, we have investigated change in optical properties and morphology of MAPbBr3 quantum dots by changing the ratio of ligands i. e oleic acid and oleylamine. Also, Rhodamine B dye has been used to notice the different context of energy/electron migration in two perovskite solutions with different properties as shown in scheme (Scheme 1). MAPbBr3 perovskite NCs have been prepared by modification of already reported ligand assisted reprecipitation technique. It will lead to formation of tunable blue to green luminescent perovksite NCs solutions.
3. Results and discussion 3.1. Optical properties and morphology characterization
2. Materials and synthesis
Blue and Green luminescent MAPbBr3 were synthesized by already reported method [10] by variation in ratio of ligands. Luminescent MAPbBr3 were obtained by rapid injection of 100 μl of white precursor solution (details Supplementary Information) to dry chloroform at room temperature. As soon as the solution was injected, change in color appears gradually (as shown in Fig. S1), implying the formation of quantum dots due to co-precipitation of CH3NH3+, Pb2+, and Br− in the presence of organic acid and amine ligands. The typical FTIR vibration modes of MAPbBr3 Perovskite Quantum Dots (PQDs) are presented in Fig. S2. The symmetric, asymmetric stretching and bending vibrational modes are explained in detail in Table S1. Good dispersibility of these quantum dots in chloroform indicates that the surface of MAPbBr3 PQD is passivated uniformly with organic ligands. The presence of oleate ligands is also supported by the NMR spectra (Fig. S3). To analyze optical properties, absorption and luminescence spectra were assessed for the colloidal solution of MAPbBr3 as shown in Fig. 1. The absorption peak of blue luminescent quantum dots is centred at 432 nm and emission at 450 nm (with excitation at 390 nm) as shown in Fig. 1 a whereas Fig. 1b shows the absorption and emission peaks of green solution at 520 and 526 nm which is close to bulk perovskites
2.1. Chemical reagents All the chemicals and solvents were procured from commercial sources were used as received. Lead (II) Bromide (99%), Methylamine solution (33 wt% in absolute ethanol) and oleylamine are purchased from Sigma Aldrich. Other reagents like Chloroform (Rankem), N,NDimethylformamide (Thomas baker), oleic acid (Merck) and Hydrobromic acid (48% in water, SRL) were ordered from local purchase. Instrumental details used for characterization and studies are listed in supplementary information. 2.2. Synthesis Here colloidal perovskite nanocrystals of MAPbBr3 were prepared by ligand-assisted reprecipitation method along with the small modification. Precursors PbBr2 and CH3NH3Br were dissolved together with oleic acid and oleylamine in good solvent dimethylformamide (DMF) resulting a transparent solution (details in supplementary information). Further, we had used chloroform as antisolvent to initiate crystallization of perovskites NCs. Many research groups have used toluene as
Fig. 1. a) Absorption and PL spectra of Blue luminescent MAPbBr3 NCs b) Absorption and PL spectra of Green Luminescent MAPbBr3 NCs. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 2
Journal of Luminescence 215 (2019) 116609
P. Bansal and P. Kar
Fig. 2. a) Absorption and PL spectra of Rhodamine dye in chloroform b) shows overlap of photo luminescent spectra of MAPbBr3 and dye.
The crystalline structure of synthesized blue and green luminescent MAPbBr3 solutions, characterized by XRD are shown in Fig. 3 (a). The concentrated solution of MAPbBr3 is deposited on the glass substrate and obtained XRD patterns are consistent with primarily reported literature [6–10]. The formed perovskite is in highly crystalline cubic phase (Pm3̅m) with lattice parameter a = 5.93 Å. Peaks of blue luminescent CH3NH3PbBr3 QDs are at 15.02⁰, 21.18⁰, 30.19⁰, 33.85⁰, 37.08⁰, 43.13⁰ and 45⁰ are the major peaks corresponding to planes (100), (110), (200), (210), (211), (220) and (300). Similarly peaks of green luminescent solution are also in cubic phase with almost same crystalline pattern and different facets as shown in Fig. 3b. Fig. 3c–e shows the typical transmission electron microscope (TEM) and High Resolution-Transmission Electron Microscope (HR-TEM) images of spherical blue luminescent CH3NH3PbBr3 quantum dots for morphological characterization. It is observed that average size of these nanoparticles is 3.5 nm as shown in Fig. 3 c and d at different scale bars. From the HR-TEM image analysis in Fig. 3 e interplanar distance fringes separation of 0.29 nm is characteristic of (002) plane as shown in XRD pattern of PQD. Inset of Fig. 3e shows Fourier transform of the SAED pattern crystalline in nature. Green luminescent MAPbBr3 NCs shows uniform nanoplates of size less than 10 nm as shown in Fig. 3 f-g.
nanocrystals, evidencing the absence of quantum size effects. Measurement of bandgap of blue and green luminescent nanocrystals is estimated as 2.88 eV and 2.39 eV respectively. The reason for the hypsochromic shift of blue luminescent perovskite solution as compared to green luminescent solution in UV and PL band is increasing concentration of organic ligands leads to decrease in thickness and size of nanoparticles formed. Also increasing concentration of ligands leads to quantum confinement effect in the nanoparticles. Blue and green luminescent perovskite solution have a small Stokes shift of 18 nm and 6 nm respectively which is attributed to the direct exciton recombination process. The absolute PL quantum yield was estimated as 17.5% for blue luminescent solution and 72.3% for green luminescent perovskite solution with integrating sphere. In order to investigate the energy transfer studies in later part we have chosen dye as rhodamine b whose absorption is found at 511 and 550 nm and emission at 575 nm is shown in Fig. 2a. Fig. 2b shows fine overlap between the emission band of green luminescent solution and absorption peak of rhodamine dye which leads to energy transfer by FRET whereas blue luminescent peak of MAPbBr3 solution is far from absorption spectra of rhodamine B dye with negligible overlap leading to electron transfer process.
Fig. 3. a) XRD Pattern of Blue luminescent MAPbBr3 NCs. b) XRD Pattern of green luminescent MAPbBr3 NCs. c) TEM image of Blue luminescent MAPbBr3 NCs at 100 nm scale bar d) TEM image of Blue luminescent MAPbBr3 NCs at 20 nm scale bar e) HR-TEM of Blue luminescent MAPbBr3 NCs. (Inset shows SAED pattern) f)TEM image of green luminescent MAPbBr3 NCs at 100 nm scale bar and g) TEM image of green luminescent MAPbBr3 NCs at 50 nm scale bar. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 3
Journal of Luminescence 215 (2019) 116609
P. Bansal and P. Kar
Fig. 4. a) Fluorescence quenching of blue luminescent MAPbBr3 NCs b) Relative changes in the emission intensity of blue luminescent MAPbBr3 NCs as a function of the concentration of dye c)FRET studies between green luminescent MAPbBr3 Nanoplates d) Relative changes in the emission intensity of green luminescent MAPbBr3 NCs as a function of the concentration of dye. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
peak at 526 nm with excitation wavelength of 450 nm. Addition of up to 1.69 μM of rhodamine B (stock solution) by consecutive addition of 10 μL in 2.5 ml of perovskite solution (details supplementary information) leads to decrease of perovskite peak at 526 nm and concomitant formation of new peak at 576 nm corresponding to PL of rhodamine dye B. This indicates energy transfer from perovskite NCs solution to rhodamine B dye as shown in Fig. 4c. Again linear behaviour is obtained by plotting Stern-volmer graph (Fig. 4d) with slope = 5.324 × 106 M−1 corresponding to rate constants which gives indication of static quenching. TEM image of green luminescent perovskite nanocrystals in the presence of dye are also shown in Fig. S6. Time-correlated single photon counting of MAPbBr3 quantum dots and nanoplates has been studied [30]. Blue luminescent MAPbBr3 was fitted in biexponential decay functions (Fig. 5a) whereas green luminescent nanoplates are fitted triexponentially (Fig. 5b). TCSPC studies of rhodamine b dye are shown in Figure S 7. Average lifetimes of these nanoparticles are calculated through lifetime parameters. Later, radiative and non radiative rate constants were calculated from quantum yield and time-resolved lifetime data using equations,
This class of perovskites is highly sensitive to electron beam damage due to which images were taken with great care to minimize exposure time to avoid changes in morphology. 3.2. Energy/electron transfer studies using rhodamine dye B These synthesized PNCs are exhibiting excellent optoelectronic properties including good light absorption as well as emission. Rhodamine B dye has high extinction coefficients and good photoluminescence quantum yield. Therefore it is used as electron acceptor for investigation of quenching of fluorescence of blue and green luminescent MAPbBr3. We prepared the perovskite solution for energy transfer studies (details in Supplementary Information). As shown in Fig. 4 a, increase of concentration of rhodamine b from 0 to 5 μM by the successive addition of 20 μL of the dye to 2.5 mL of the blue luminescent perovskite donor solution leads to quenching of luminescent peak of perovskite NCs at 450 nm (details of stock solution in supplementary information). 415 nm was selected as the excitation wavelength. The low quantum yield and very small overlap of it with absorbance of dye gives no probability of Förster Resonance Energy Transfer (FRET). We have observed emission quenching in this solution as aggregation of perovskite nanocrystals are induced along with rhodamine b dye. When the dye concentration reached up to 5 μM, there is quenching of 80% of perovskite solution along with rise of new peak formation. Small rise of peak at 480 nm indicates aggregation of nanocrystals with dye that is further confirmed through TEM imaging as shown in Fig. S4 along with EDX (Fig. S5). They possess high surface area at nanoscale which interacts with suitable acceptor dye through electrostatic forces and leads to interfacial energy/electron transfer. On plotting Stern-volmer graph between relative emission intensity of donor in fluorescence and concentration of acceptor, we observed linear behaviour with blue luminescent perovskite solution as shown in Fig. 4b. The Stern–Volmer constant (KSV) is determined by the following equation:
τavg =
(A1 τ12 + A2 τ22) A1 τ1 + A2 τ2
ΦPL = kr τavg τavg =
1 (kr + knr )
where τavg is average life time, A1, A2 and A3 are pre-exponential factors for corresponding first, τ1 and other two lifetime component, τ2, τ3 ΦPL is quantum yield, kr and knr are radiative and non radiative constants (details of parameters are shown in Table 1). The average lifetime of blue and green luminescent MAPbBr3 is calculated as 26.06 ns and 29.33 ns which is very short because of small size of quantum dots and nanoplates. Radiative and non radiative constants of blue luminescent MAPbBr3 NCs is calculated as 6.52 × 106 s−1 and 31.85 × 106 s−1 whereas for green luminescent NCs is calculated as 24.54 × 106 s−1 and 94.6 × 106 s−1. In the biexponential decay, there are two short lived and long lived components. Longest time in blue nanocrystals is associated to trapped
I ′/ I = (1 + Ksv [Q]) From the slope of plots, Ksv for blue luminescent perovskite is calculated as 5.53 × 105 M−1. For green luminescent solution, we observed photoluminescence 4
Journal of Luminescence 215 (2019) 116609
P. Bansal and P. Kar
Fig. 5. a) Time resolved decay studies of Blue Luminescent Perovskite NCs in the absence and presence of dye b) Time resolved decay studies of green luminescent Perovskite NCs in the absence and presence of dye. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Roorkee. P.K gratefully acknowledges the Department of Science & Technology (SB/FT/CS-135/2012), New Delhi, India for financial support. This work was partially supported by the Council of Scientific & Industrial Research (CSIR (01(2796)/14/EMR-II) and CSIR (01(2990)/19/EMR-II), New Delhi, India. Authors acknowledge Institute Instrumentation Centre, IIT Roorkee, for providing various instrumental facilities. PB acknowledges MHRD, India, for her junior research fellowship.
Table 1 Shows details of parameters related to time resolved decay parameters.
BL MAPbBr3 NCs BL MAPbBr3 NCs + RD GL MAPbBr3 NCs GL MAPbBr3 NCs + RD
τ1 (ns)
τ2 (ns)
τ3 (ns)
τavg (ns)
A1
A2
A3
12.32 14.41
32.54 36.35
– 5.2
55.46 68.49
44.54 16.42
– 16.09
26.06 21.80
12.60 20.84
45.3 0.754
3.19 4.64
59.09 59.49
18.90 17.75
22 27.76
29.33 15.44
Appendix A. Supplementary data excitons that contribute 55.46% of total decay. Decay time around 12 ns are probably due to free exciton recombination. In blue nanocrystals there is appearance of more decay time that is 5.2 ns, due to the aggregation of nanoparticles in the presence of rhodamine b dye as indicated from the new peak generated with bathochromic shift at 480 nm in PL spectra. Time resolved decay of blue luminescent perovskite in the presence of dye is fitted triexponentially in which average lifetime of perovskite in the presence of dye is decreases to 21.80 ns. Green luminescent nanoplates are having short lived, intermediate and long lived components. In green nanocrystals relaxation time of trapped states increases and their contribution to emission decreases, evidencing the lower role of defects related luminescence and increases PLQY while the fastest time in green nanocrystals is related to some defect. TCSPC studies for green luminescent nanoplates further confirmed the decreases in average lifetime from 29.33 ns to 15.44 ns in the presence of dye and suggests the probability of FRET mechanism. Also, concentration dependent TCSPC studies of blue and green luminescent MAPbBr3 perovskite nanocrystals are performed as shown in Fig. S8 with details of parameters are highlighted in Tables S2 and S3. On increasing the concentration of rhodamine b dye in blue as well as green luminescent MAPbBr3 perovskite nanocrystals, there is more decrease in average lifetime which confirms the FRET.
Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jlumin.2019.116609. References [1] P.V. Kamat, J. Phys. Chem. C 112 (2008) 18737–18753. [2] H.J. Snaith, J. Phys. Chem. Lett. 4 (2013) 3623–3630. [3] D.V. Talapin, J.S. Lee, M.V. Kovalenko, E.V. Shevchenko, Chem. Rev. 110 (2010) 389–458. [4] A.R. Kirmani, A. Kiani, M.M. Said, O. Voznyy, N. Wehbe, G. Walters, S. Barlow, E.H. Sargent, S.R. Marder, A. Amassian, ACS Energy Lett 1 (2016) 922–930. [5] A.J. Nozik, Phys. Met. 14 (2002) 115–120. [6] a) L.C. Schmidt, A. Pertegȧs, S. Gonzȧlez-Carrero, O. Malinkiewicz, S. Agouram, G. Minguez Espallargas, H.J. Bolink, R.E. Galian, J. Pérez-Prieto, J. Am. Chem. Soc. 136 (2014) 850–853; b) J.D. Roo, M. Ibáñez, P. Geiregat, G. Nedelcu, W. Walravens, J. Maes, J.C. Martins, I.V. Driessche, M.V. Kovalenko, Z. Hens, ACS Nano 10 (2016) 2071–2081. [7] L. Protesescu, S. Yakunin, M.I. Bodnarchuk, F. Krieg, R. Caputo, C.H. Hendon, R.X. Yang, A. Walsh, M.V. Kovalenko, Nano Lett. 15 (2015) 3692–3696. [8] a) D. Zhang, S.W. Eaton, Y. Yu, L. Dou, P. Yong, J. Am. Chem. Soc. 137 (2015) 9230–9233; b) A. Manzi, Y. Tong, J. Feucht, E.-P. Yao, L. Polavarapu, A.S. Urban, J. Feldmann, Nat. Commun. 9 (2018) 1518. [9] a) J.A. Christians, P.A. Miranda Herrera, P.V. Kamat, J. Am. Chem. Soc. 137 (2015) 1530–1538; b) B.J. Bohn, T. Simon, M. Gramlich, A.F. Richter, L. Polavarapu, A.S. Urban, J. Feldman, ACS Photonics 5 (2018) 648–654. [10] a) H. Huang, L. Polavarapu, J.A. Sichert, A.S. Susha, A.S. Urban, A.L. Rogach, NPG Asia Mater. 8 (2016) e328; b) P. Bansal, Y. Khan, G.K. Nim, P. Kar, Chem. Commun. (J. Chem. Soc. Sect. D) 54 (2018) 3508–3511; c) Y. Xin, H. Zhao, J. Zhang, ACS Appl. Mater. Interfaces 10 (2018) 4971–4980. [11] J.A. Sichert, Y. Tong, N. Mutz, M. Vollmer, S. Fischer, K.Z. Milowska, R. Garcia Cortadella, B. Nickel, C. Cardenas -Daw, J.K. Stolarczyk, A.S. Urban, J. Feldman, Nano Lett. 15 (2015) 6521–6527. [12] Y. Kim, E. Yassitepe, O. Voznyy, R. Comin, G. Walters, X. Gong, P. Kanjanaboos, A.F. Nogueira, E.H. Sargent, ACS Appl. Mater. Interfaces 7 (2015) 25007–25013. [13] Y. Tong, F. Ehart, W. Vanderlinden, C. Cardenas - Daw, J.K. Stolarczyk, L. Polavarapu, A.S. Urban, ACS Nano 10 (2016) 10936–10944. [14] L. Dou, A.B. Wong, Y. Yu, M. Lai, N. Kornienko, S.W. Eaton, A. Fu, C.G. Bischak, J. Ma, T. Ding, N.S. Ginsberg, L.W. Wang, A.P. Alivisatos, P. Yang, Science 349 (2015) 1518–1521. [15] P. Tyagi, S.M. Arveson, W.A. Tisdale, J. Phys. Chem. Lett. 6 (2015) 1911–1916. [16] L. Liu, S. Huang, L. Pan, L.-J. Shi, B. Zou, L. Deng, H. Zhong, Angew. Chem. Int. Ed. 56 (2017) 1780–1783. [17] G. Li, Z.-K. Tan, D. Di, M.L. Lai, L. Jiang, J.H.-W. Lim, R.H. Friend, N.C. Greenham, Nano Lett. 15 (2015) 2640–2644. [18] S. Gonzalez-Carrero, R.E. Galian, J. P′erez-Prieto, J. Mater. Chem. 3 (2015) 9187–9193. [19] L. Liu, S. Huang, L. Pan, L.-J. Shi, B. Zou, L. Deng, H. Zhong, Angew. Chem. Int. Ed.
4. Conclusions In summary, MAPbBr3 Nanoparticles are synthesized by tuning the ratio of oleic acid and oleylamine. These nanoparticles possess different optical properties, size and morphology. Energy transfer studies have been investigated by using electron acceptor rhodamine b dye which is very helpful for light harvesting materials. These nanocrystals act as superior absorber and electron donor in place of conventional semiconductors. In this way, Perovskite nanocrystals have opened a new avenue for energy transfer and light harvesting materials. Conflicts of interest There are no conflicts to declare. Acknowledgements This work was partially supported by Indian Institute of Technology 5
Journal of Luminescence 215 (2019) 116609
P. Bansal and P. Kar
[26] C. Muthu, A. Vijayan, V.C. Nair, Chem. Asian J. 12 (2017) 988–995. [27] Z. Liang, M. Kang, G.F. Payne, X. Wang, R. Sun, ACS Appl. Mater. Interfaces 8 (2016) 17478–17488. [28] S.S. Dandpat, P.K. Sahu, M. Sarkar, Chemistry Select 1 (2016) 2290–2298. [29] K. Virkki, S. Demir, H. Lemmetyinen, N.V. Tkachenko, J. Phys. Chem. C 119 (2015) 17561−21767. [30] J.R. Lakowicz, Principles of Fluorescence Spectroscopy, third ed., Springer, New York, 2006.
56 (2017) 1780–1783. S.T. Ha, R. Su, J. Xing, Q. Zhang, Q. Xiong, Che. Sci. 8 (2017) 2522–2536. J.B. Hoffman, H. Choi, P.V. Kamat, J. Phys. Chem. C 118 (2014) 18453–18461. J.B. Hoffman, R. Alam, P.V. Kamat, ACS Energy Lett 2 (2017) 391–396. A. Ajayaghosh, V.K. Praveen, C. Vijayakumar, Chem. Soc. Rev. 37 (2008) 109–122. C. Weerd, L. Gomez, H. Zhang, W.J. Buma, G. Nedelcu, M.V. Kovalenko, T. Gregorkiewicz, J. Phys. Chem. C 120 (2016) 13310–13315. [25] J.-H. Yum, B.E. Hardin, S.-J. Moon, E. Baranoff, F. Nesch, M.D. McGehee, M. Gratzel, M.K. Nazeeruddin, Angew. Chem. Int. Ed. 48 (2009) 9277–9280. [20] [21] [22] [23] [24]
6
Contents lists available at ScienceDirect
Journal of Luminescence journal homepage: www.elsevier.com/locate/jlumin
Probing the energy transfer process by controlling the morphology of CH3NH3PbBr3 nanocrystals with rhodamine B dye
T
Parul Bansal, Prasenjit Kar∗ Department of Chemistry, Indian Institute of Technology (IIT), Roorkee, Haridwar, Uttarakhand, 247667, India
A R T I C LE I N FO
A B S T R A C T
Keywords: Nanostructures Photoluminescence FRET Morphology Rhodamine B
A facile synthesis of tunable blue to green luminescent colloidal MAPbBr3 Perovskite NCs is synthesized by solution processed ligand assisted re-precipitation technique (LARP). Different behaviour in optical properties and morphology of MAPbBr3 perovskite NCs has been observed by tuning the ratio of oleic acid and oleylamine. Rhodamine B has been chosen as dye to study electron migration between perovskite NCs and dye. It has been investigated that both blue and green luminescent nanoparticles leads to different energy transfer behaviour with dye. Green luminescent MAPbBr3 nanoparticles are able to show Förster Resonance Energy Transfer whereas in blue luminescent nanoparticles, there is fluorescence quenching because of aggregation between perovskite and rhodamine b dye. These studies have been utilized in study of different interaction between tunable perovskite and rhodamine B dye.
1. Introduction The expectation of low cost clean energy has led to deviation towards research of new materials and processes to achieve strategies for light harvesting in photovoltaics [1–3]. Earlier a lot of investigations have been performed using semiconductor quantum dots (QDs) which possess tunability in band gap and makes ideal candidates as light harvesters in quantum dot solar cells (QDSCs) [3–5]. Recently organometal halide perovskites have exhibited a prodigious potential not only in LED devices but also photovoltaic applications [6–8]. The earliest studies on perovskites have been done in 70s but perovskite nanocrystals (NCs) attract the interest of the scientific community in recent years. These nanoparticles are having various applications in photovoltaic solar cells, sensors, light emitting diodes, lasers, photodetectors [6–14]. Perovskite nanocrystals are particularly ensembled for such applications due to their high absorption cross-section, narrow emission band, high quantum yield and recently, used as donors in nanocrystal–dye FRET couple [8–14,26]. However, instability and sensitivity of these materials towards moisture leads to difficulty in confining their applications [10]. The first solution based colloidal MAPbBr3 NCs was reported by Pérez -Prieto et al.6. The absorption and PL peaks of these nanocrystalline materials were reported as 527 nm and 530 nm respectively with the PLQY value of 20%. Later, Tyagi et al. have revealed the blue shift in absorption peak of MAPbBr3 with respect to bulk MAPbBr3 and
∗
introduced the concept of quantum confinement in size of MAPbBr3 nanocrystals [15]. A lot of studies have been performed on ligand, temperature, concentration, time dependent tunability in optical studies and morphology of nanoparticles [14–20] but a lot of studies are still under exploration. Energy transfer is the unique concept introduced from photosynthesis. It is a process where an excited donor interacts with a relaxed acceptor, resulting in a relaxed donor and excited acceptor [21,22]. Generally they follow nonradiative pathways including Förster Resonance Energy Transfer, Dexter Energy Transfer, collisional quenching and exciplex state [21–24]. Energy transfer studies between quantum dot-quantum dot, quantum dot - dye and other systems have been probed in conventional semiconductor quantum dots such as CdS, CdSe etc through Van der waals interactions and other supramolecular systems [21–25]. Till now hybrid perovskite nanocrystals have been explored mostly as light emitting diodes [8–10]. These perovskite materials have more challenging properties as compared to conventional semiconductors and equally serve as light harvesting materials. Muthu et al. were the one who reported light harvesting antenna properties of hybrid perovskites with different dyes through FRET mechanism [26]. These energy and electron transfer processes are very important for advanced optoelectronic devices [27–29]. Hybrid perovskites are having two unique properties: intense absorption in visible range and excellent photoluminescence with high quantum yield which makes them superior applicants for energy
Corresponding author E-mail addresses: [email protected], [email protected] (P. Kar).
https://doi.org/10.1016/j.jlumin.2019.116609 Received 21 February 2019; Received in revised form 30 June 2019; Accepted 5 July 2019 Available online 06 July 2019 0022-2313/ © 2019 Elsevier B.V. All rights reserved.
Journal of Luminescence 215 (2019) 116609
P. Bansal and P. Kar
Scheme 1. Schematic illustration of Different energy transfer behaviour of MAPbBr3 perovskite NCs with rhodamine dye.
antisolvent [10] while in this report all the experiments were carried out in dry chloroform. By changing the concentration of capping ligands, oleic acid and oleylamine as 100 μl and 200 μl, we had obtained blue luminescent quantum dots of MAPbBr3 (Scheme 1). Whereas keeping oleic acid as 200 μl and oleylamine as 32 μl had lead to formation of green luminescent perovskite solution.
transfer and storage purposes [6,10,18]. In this report, we have investigated change in optical properties and morphology of MAPbBr3 quantum dots by changing the ratio of ligands i. e oleic acid and oleylamine. Also, Rhodamine B dye has been used to notice the different context of energy/electron migration in two perovskite solutions with different properties as shown in scheme (Scheme 1). MAPbBr3 perovskite NCs have been prepared by modification of already reported ligand assisted reprecipitation technique. It will lead to formation of tunable blue to green luminescent perovksite NCs solutions.
3. Results and discussion 3.1. Optical properties and morphology characterization
2. Materials and synthesis
Blue and Green luminescent MAPbBr3 were synthesized by already reported method [10] by variation in ratio of ligands. Luminescent MAPbBr3 were obtained by rapid injection of 100 μl of white precursor solution (details Supplementary Information) to dry chloroform at room temperature. As soon as the solution was injected, change in color appears gradually (as shown in Fig. S1), implying the formation of quantum dots due to co-precipitation of CH3NH3+, Pb2+, and Br− in the presence of organic acid and amine ligands. The typical FTIR vibration modes of MAPbBr3 Perovskite Quantum Dots (PQDs) are presented in Fig. S2. The symmetric, asymmetric stretching and bending vibrational modes are explained in detail in Table S1. Good dispersibility of these quantum dots in chloroform indicates that the surface of MAPbBr3 PQD is passivated uniformly with organic ligands. The presence of oleate ligands is also supported by the NMR spectra (Fig. S3). To analyze optical properties, absorption and luminescence spectra were assessed for the colloidal solution of MAPbBr3 as shown in Fig. 1. The absorption peak of blue luminescent quantum dots is centred at 432 nm and emission at 450 nm (with excitation at 390 nm) as shown in Fig. 1 a whereas Fig. 1b shows the absorption and emission peaks of green solution at 520 and 526 nm which is close to bulk perovskites
2.1. Chemical reagents All the chemicals and solvents were procured from commercial sources were used as received. Lead (II) Bromide (99%), Methylamine solution (33 wt% in absolute ethanol) and oleylamine are purchased from Sigma Aldrich. Other reagents like Chloroform (Rankem), N,NDimethylformamide (Thomas baker), oleic acid (Merck) and Hydrobromic acid (48% in water, SRL) were ordered from local purchase. Instrumental details used for characterization and studies are listed in supplementary information. 2.2. Synthesis Here colloidal perovskite nanocrystals of MAPbBr3 were prepared by ligand-assisted reprecipitation method along with the small modification. Precursors PbBr2 and CH3NH3Br were dissolved together with oleic acid and oleylamine in good solvent dimethylformamide (DMF) resulting a transparent solution (details in supplementary information). Further, we had used chloroform as antisolvent to initiate crystallization of perovskites NCs. Many research groups have used toluene as
Fig. 1. a) Absorption and PL spectra of Blue luminescent MAPbBr3 NCs b) Absorption and PL spectra of Green Luminescent MAPbBr3 NCs. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 2
Journal of Luminescence 215 (2019) 116609
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Fig. 2. a) Absorption and PL spectra of Rhodamine dye in chloroform b) shows overlap of photo luminescent spectra of MAPbBr3 and dye.
The crystalline structure of synthesized blue and green luminescent MAPbBr3 solutions, characterized by XRD are shown in Fig. 3 (a). The concentrated solution of MAPbBr3 is deposited on the glass substrate and obtained XRD patterns are consistent with primarily reported literature [6–10]. The formed perovskite is in highly crystalline cubic phase (Pm3̅m) with lattice parameter a = 5.93 Å. Peaks of blue luminescent CH3NH3PbBr3 QDs are at 15.02⁰, 21.18⁰, 30.19⁰, 33.85⁰, 37.08⁰, 43.13⁰ and 45⁰ are the major peaks corresponding to planes (100), (110), (200), (210), (211), (220) and (300). Similarly peaks of green luminescent solution are also in cubic phase with almost same crystalline pattern and different facets as shown in Fig. 3b. Fig. 3c–e shows the typical transmission electron microscope (TEM) and High Resolution-Transmission Electron Microscope (HR-TEM) images of spherical blue luminescent CH3NH3PbBr3 quantum dots for morphological characterization. It is observed that average size of these nanoparticles is 3.5 nm as shown in Fig. 3 c and d at different scale bars. From the HR-TEM image analysis in Fig. 3 e interplanar distance fringes separation of 0.29 nm is characteristic of (002) plane as shown in XRD pattern of PQD. Inset of Fig. 3e shows Fourier transform of the SAED pattern crystalline in nature. Green luminescent MAPbBr3 NCs shows uniform nanoplates of size less than 10 nm as shown in Fig. 3 f-g.
nanocrystals, evidencing the absence of quantum size effects. Measurement of bandgap of blue and green luminescent nanocrystals is estimated as 2.88 eV and 2.39 eV respectively. The reason for the hypsochromic shift of blue luminescent perovskite solution as compared to green luminescent solution in UV and PL band is increasing concentration of organic ligands leads to decrease in thickness and size of nanoparticles formed. Also increasing concentration of ligands leads to quantum confinement effect in the nanoparticles. Blue and green luminescent perovskite solution have a small Stokes shift of 18 nm and 6 nm respectively which is attributed to the direct exciton recombination process. The absolute PL quantum yield was estimated as 17.5% for blue luminescent solution and 72.3% for green luminescent perovskite solution with integrating sphere. In order to investigate the energy transfer studies in later part we have chosen dye as rhodamine b whose absorption is found at 511 and 550 nm and emission at 575 nm is shown in Fig. 2a. Fig. 2b shows fine overlap between the emission band of green luminescent solution and absorption peak of rhodamine dye which leads to energy transfer by FRET whereas blue luminescent peak of MAPbBr3 solution is far from absorption spectra of rhodamine B dye with negligible overlap leading to electron transfer process.
Fig. 3. a) XRD Pattern of Blue luminescent MAPbBr3 NCs. b) XRD Pattern of green luminescent MAPbBr3 NCs. c) TEM image of Blue luminescent MAPbBr3 NCs at 100 nm scale bar d) TEM image of Blue luminescent MAPbBr3 NCs at 20 nm scale bar e) HR-TEM of Blue luminescent MAPbBr3 NCs. (Inset shows SAED pattern) f)TEM image of green luminescent MAPbBr3 NCs at 100 nm scale bar and g) TEM image of green luminescent MAPbBr3 NCs at 50 nm scale bar. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.) 3
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Fig. 4. a) Fluorescence quenching of blue luminescent MAPbBr3 NCs b) Relative changes in the emission intensity of blue luminescent MAPbBr3 NCs as a function of the concentration of dye c)FRET studies between green luminescent MAPbBr3 Nanoplates d) Relative changes in the emission intensity of green luminescent MAPbBr3 NCs as a function of the concentration of dye. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
peak at 526 nm with excitation wavelength of 450 nm. Addition of up to 1.69 μM of rhodamine B (stock solution) by consecutive addition of 10 μL in 2.5 ml of perovskite solution (details supplementary information) leads to decrease of perovskite peak at 526 nm and concomitant formation of new peak at 576 nm corresponding to PL of rhodamine dye B. This indicates energy transfer from perovskite NCs solution to rhodamine B dye as shown in Fig. 4c. Again linear behaviour is obtained by plotting Stern-volmer graph (Fig. 4d) with slope = 5.324 × 106 M−1 corresponding to rate constants which gives indication of static quenching. TEM image of green luminescent perovskite nanocrystals in the presence of dye are also shown in Fig. S6. Time-correlated single photon counting of MAPbBr3 quantum dots and nanoplates has been studied [30]. Blue luminescent MAPbBr3 was fitted in biexponential decay functions (Fig. 5a) whereas green luminescent nanoplates are fitted triexponentially (Fig. 5b). TCSPC studies of rhodamine b dye are shown in Figure S 7. Average lifetimes of these nanoparticles are calculated through lifetime parameters. Later, radiative and non radiative rate constants were calculated from quantum yield and time-resolved lifetime data using equations,
This class of perovskites is highly sensitive to electron beam damage due to which images were taken with great care to minimize exposure time to avoid changes in morphology. 3.2. Energy/electron transfer studies using rhodamine dye B These synthesized PNCs are exhibiting excellent optoelectronic properties including good light absorption as well as emission. Rhodamine B dye has high extinction coefficients and good photoluminescence quantum yield. Therefore it is used as electron acceptor for investigation of quenching of fluorescence of blue and green luminescent MAPbBr3. We prepared the perovskite solution for energy transfer studies (details in Supplementary Information). As shown in Fig. 4 a, increase of concentration of rhodamine b from 0 to 5 μM by the successive addition of 20 μL of the dye to 2.5 mL of the blue luminescent perovskite donor solution leads to quenching of luminescent peak of perovskite NCs at 450 nm (details of stock solution in supplementary information). 415 nm was selected as the excitation wavelength. The low quantum yield and very small overlap of it with absorbance of dye gives no probability of Förster Resonance Energy Transfer (FRET). We have observed emission quenching in this solution as aggregation of perovskite nanocrystals are induced along with rhodamine b dye. When the dye concentration reached up to 5 μM, there is quenching of 80% of perovskite solution along with rise of new peak formation. Small rise of peak at 480 nm indicates aggregation of nanocrystals with dye that is further confirmed through TEM imaging as shown in Fig. S4 along with EDX (Fig. S5). They possess high surface area at nanoscale which interacts with suitable acceptor dye through electrostatic forces and leads to interfacial energy/electron transfer. On plotting Stern-volmer graph between relative emission intensity of donor in fluorescence and concentration of acceptor, we observed linear behaviour with blue luminescent perovskite solution as shown in Fig. 4b. The Stern–Volmer constant (KSV) is determined by the following equation:
τavg =
(A1 τ12 + A2 τ22) A1 τ1 + A2 τ2
ΦPL = kr τavg τavg =
1 (kr + knr )
where τavg is average life time, A1, A2 and A3 are pre-exponential factors for corresponding first, τ1 and other two lifetime component, τ2, τ3 ΦPL is quantum yield, kr and knr are radiative and non radiative constants (details of parameters are shown in Table 1). The average lifetime of blue and green luminescent MAPbBr3 is calculated as 26.06 ns and 29.33 ns which is very short because of small size of quantum dots and nanoplates. Radiative and non radiative constants of blue luminescent MAPbBr3 NCs is calculated as 6.52 × 106 s−1 and 31.85 × 106 s−1 whereas for green luminescent NCs is calculated as 24.54 × 106 s−1 and 94.6 × 106 s−1. In the biexponential decay, there are two short lived and long lived components. Longest time in blue nanocrystals is associated to trapped
I ′/ I = (1 + Ksv [Q]) From the slope of plots, Ksv for blue luminescent perovskite is calculated as 5.53 × 105 M−1. For green luminescent solution, we observed photoluminescence 4
Journal of Luminescence 215 (2019) 116609
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Fig. 5. a) Time resolved decay studies of Blue Luminescent Perovskite NCs in the absence and presence of dye b) Time resolved decay studies of green luminescent Perovskite NCs in the absence and presence of dye. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Roorkee. P.K gratefully acknowledges the Department of Science & Technology (SB/FT/CS-135/2012), New Delhi, India for financial support. This work was partially supported by the Council of Scientific & Industrial Research (CSIR (01(2796)/14/EMR-II) and CSIR (01(2990)/19/EMR-II), New Delhi, India. Authors acknowledge Institute Instrumentation Centre, IIT Roorkee, for providing various instrumental facilities. PB acknowledges MHRD, India, for her junior research fellowship.
Table 1 Shows details of parameters related to time resolved decay parameters.
BL MAPbBr3 NCs BL MAPbBr3 NCs + RD GL MAPbBr3 NCs GL MAPbBr3 NCs + RD
τ1 (ns)
τ2 (ns)
τ3 (ns)
τavg (ns)
A1
A2
A3
12.32 14.41
32.54 36.35
– 5.2
55.46 68.49
44.54 16.42
– 16.09
26.06 21.80
12.60 20.84
45.3 0.754
3.19 4.64
59.09 59.49
18.90 17.75
22 27.76
29.33 15.44
Appendix A. Supplementary data excitons that contribute 55.46% of total decay. Decay time around 12 ns are probably due to free exciton recombination. In blue nanocrystals there is appearance of more decay time that is 5.2 ns, due to the aggregation of nanoparticles in the presence of rhodamine b dye as indicated from the new peak generated with bathochromic shift at 480 nm in PL spectra. Time resolved decay of blue luminescent perovskite in the presence of dye is fitted triexponentially in which average lifetime of perovskite in the presence of dye is decreases to 21.80 ns. Green luminescent nanoplates are having short lived, intermediate and long lived components. In green nanocrystals relaxation time of trapped states increases and their contribution to emission decreases, evidencing the lower role of defects related luminescence and increases PLQY while the fastest time in green nanocrystals is related to some defect. TCSPC studies for green luminescent nanoplates further confirmed the decreases in average lifetime from 29.33 ns to 15.44 ns in the presence of dye and suggests the probability of FRET mechanism. Also, concentration dependent TCSPC studies of blue and green luminescent MAPbBr3 perovskite nanocrystals are performed as shown in Fig. S8 with details of parameters are highlighted in Tables S2 and S3. On increasing the concentration of rhodamine b dye in blue as well as green luminescent MAPbBr3 perovskite nanocrystals, there is more decrease in average lifetime which confirms the FRET.
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4. Conclusions In summary, MAPbBr3 Nanoparticles are synthesized by tuning the ratio of oleic acid and oleylamine. These nanoparticles possess different optical properties, size and morphology. Energy transfer studies have been investigated by using electron acceptor rhodamine b dye which is very helpful for light harvesting materials. These nanocrystals act as superior absorber and electron donor in place of conventional semiconductors. In this way, Perovskite nanocrystals have opened a new avenue for energy transfer and light harvesting materials. Conflicts of interest There are no conflicts to declare. Acknowledgements This work was partially supported by Indian Institute of Technology 5
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