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Pressure effect on CH3NH3PbBr3 perovskite films deposited by close space sublimation for PIN diode and its possible application in radiation detector
Materials Science in Semiconductor Processing 110 (2020) 104965
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Pressure effect on CH3NH3PbBr3 perovskite films deposited by close space sublimation for PIN diode and its possible application in radiation detector �nchez * Gibr�an G. Martínez-Falomir , C.A. Lopez-Lazcano , J.L. Almaral-Sa � Universidad Aut� onoma de Sinaloa, Fuente de Poseid� on y Prol., Angel Flores S/N, C.P.81223, Los Mochis, Sinaloa, Mexico
A R T I C L E I N F O
A B S T R A C T
Keywords: CSS Pressure effect MAPbBr3 perovskite Diode application
In this work, methylammonium lead bromide (CH3NH3PbBr3) perovskite films are deposited by close space sublimation (CSS), by two steps, the first layer is lead bromide (PbBr2) and the second is methylammonium � bromide (MABr). Pressure effect on the films, from 1000 psi to 5000 psi at 100 C temperature, was studied. Perovskite films were characterized by XRD, UV–Vis, SEM, AFM, PESA and Kelvin probe. The results show a cubic structure perovskite (XRD), band gap of 2.28 eV (UV–Vis), 3 μm thickness and uniform grain distribution (SEM), roughness reduction from 118 nm to 6 nm (AFM), valence band of 5.0 eV (PESA) and work function from 4.8 to 5 eV (Kelvin probe). These properties could allow to use as radiation detector diode.
1. Introduction A new generation of hybrid perovskite materials with ABX3 struc ture; where, A is an organic cation, such as methylammonium (MA), B is an inorganic cation (Pb), and X is a halogen anion (Br), have attracted the attention due to its several applications such as solar cells structures [1–14], transistors (200–500 nm thicknesses) [15] and light-emitting nanoparticles [16], hybrid crystals, as radiation detector for alphas particles [17], x-rays [18], or neutrons [19]. CH3NH3PbBr3 (MAPbBr3) perovskite has a direct band-gap of 2.18–2.3 eV, with a small difference between films and crystals [20,21], although could obtain modifications on morphology by manipulating thermal annealing [22], it has not been possible without changing its structure [23]. In this perovskite the inorganic cation is an important factor to determinate electronic properties when used for devices ap plications [24], wich is associated with electronic and magnetic prop erties in combination with thermal and mechanical stability [25]. MAPbBr3 perovskite mechanical properties at room temperature are well known, its elastic region for loads up to 5–6 mN, before reaching the plastic deformation zone. Roughness is an usual problem for thick films in electronic devices: if this value is higher than the subsequent layer a short-circuit may occur between them [26]. Spin coating and inverse temperature crystalization are traditional deposition methods have been used to obtain high quality perovskites [27–30], but unlike them, close space sublimation (CSS) technique has some advantage, because it allows to estimate the films optimal
deposition conditions, use high vacuum and ramps control at tempera ture and time [31], also it is possible to obtain thick films in micrometers scale, controlling parameters in: crucible and substrate (temperature and gap) and chamber (pressure, temperature and gas type) [32]. These characteristics make CSS better than similar techniques, such as: close-spaced vacuum sublimation (CSVS) [33], hot wall epitaxy (HWE) [34,35] and quasi-close volume (QCV) [36]. The neutron radiation as its name implies is a neutron particle, so the detection methods for this kind of radiation are by indirect methods, one of those, is by capturing the neutron with a conversion layer usually LiF or 10B [37]. When the neutron is captured by 10B produces a decay re action where alphas and Li ions are emitted, the most possible reaction produces α-particles with energy of 1.47 MeV. Therefore if the material it is capable to detect α-particles also it would detect neutrons. Then a film with a high thickness, in orders of micrometers (μm) will be capable to stop α-particles from the reaction between a neutron and 10B layer [38]. In this work, we deposited MAPbBr3 perovskite films by CSS, improving morphology surface with a hot press system, applying tem � perature (100 C) and pressure at 1.8, 13.7, 20.6, 27.5, and 34.4 MPa (1000, 2000, 3000, 4000 and 5000 psi) over an area of 0.000625 m2 (1 square inches), which it meant a stress on the surface of 1, 8, 12, 17, and 21 kN. The hot press effect on the perovskites decreased roughness from 118 nm to 6 nm and 3 μm thickness was obtained. MAPbBr3 perovskite film properties regardless to radiation sensi tivity and also the results of thickness and diode behaviour could be a
* Corresponding author. E-mail address: [email protected] (J.L. Almaral-S� anchez). https://doi.org/10.1016/j.mssp.2020.104965 Received 8 November 2019; Received in revised form 21 January 2020; Accepted 24 January 2020 Available online 5 February 2020 1369-8001/© 2020 Elsevier Ltd. All rights reserved.
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Materials Science in Semiconductor Processing 110 (2020) 104965
2.3. Characterization of MAPbBr3 The crystalline structure of the perovskite films were obtained by Xray diffraction (XRD) using a Rigaku Ultima III X-ray diffractometer, using Cu Kα radiation. All the data was obtained at the scan speed of 0.5� /min. After background subtraction, the intensity profile were expanded into WinJade program (Williamson-Hall method). The morphology was studied by scanning electron microscope (SEM) using a
Fig. 1. Schematic of the close space sublimation (CSS) chamber.
great support for future applications in radiation detector. 2. Experimental 2.1. Materials Lead bromide (PbBr2), 98þ % pure and methylammonium bromide (MABr) were purchased from Alfa Aesar and Luminescence Technology Corporation, respectively. 2.2. Deposition of MAPbBr3 perovskite films by close space sublimation (CSS)
Fig. 3. Device structure for ITO/NiO/MAPbBr3/ZnO/Al diode.
The CSS equipment has top (crucible) and down (substrate) heaters, both of them are used to control the temperature independently. The substrates were glass, glass/Au and ITO/NiO. Fig. 1 shows a schematic of the close space sublimation (CSS) chamber. The deposition of MAPbBr3 is achieved by the sequential deposition (two steps) of PbBr2 and MABr at 90 mTorr deposition pressure. Fig. 2 shows depositions parameters in a) the first step (PbBr2), with � error bars at 10 C, four temperatures ramps of 300 s each were applied simultaneously onto both, substrate (s) and crucible (c), to obtain the � � film. The first ramp was at 25 C, the second ramp was 200 C, and 175 � � � C, third and fourth ramp were 400 C and 225 C for substrate and crucible heater, respectively. Fig. 2 b) second step (MABr) onto the � PbBr2 film, facing up toward precursor, with error bars at 10 C. We programmed temperatures four ramps. From ramp one to three, 300 s for both (up and down) and fourth ramp, 4500 s. The same temperature for crucible and MABr film was applied in both, the first and second � � ramp, using 25 C and 100 C, respectively; third and fourth ramp were � � 100 C and 175 C, for crucible and MABr, respectively. The perovskite thickness can be controlled considering time, temperature and vacuum pressure into CSS chamber. MAPbBr3 perovskites films were applied at no anneal-no pressure � � (S1), 100 C-no pressure (S2), and by hot press system at 100 C-1000 psi � � � (S3), 100 C-2000 psi (S4), 100 C-3000 psi (S5), 100 C-4000 psi (S6) � � and 100 C-5000 psi (S7) by 3 h each, with 2 C of error bar.
Fig. 4. X-rays diffraction patterns of MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7.
Fig. 2. Depositions parameters to obtain a) PbBr2 and b) MABr. 2
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Materials Science in Semiconductor Processing 110 (2020) 104965
Table 1 Calculated values of crystallite size, microstrain, dislocation density and lattice parameter of MAPbBr3 at different conditions. 3
(nm 2)
No.
2θ (� )
β(� )
D (nm)
δ x 10
1 2 3 4 5 6 7
14.83635 21.13377 30.06349 33.7314 37.12903 43.08191 45.82614
0.34884 0.33859 0.30278 0.29638 0.29423 0.29106 0.2764
22.965663 23.8676167 27.1674339 28.0091483 28.4852288 29.343845 31.2041107
1.896016114 1.755423431 1.354886022 1.274677128 1.23242522 1.161357586 1.02701404
ε x10
3
11.69049764 7.919609543 4.919608452 4.265607071 3.822235754 3.217308476 2.853239225
� � Cos2 θ Cos2 θ þ 1=2 Sen θ θ 1.8570 1.2273 0.7726 0.6330 0.5353 0.3967 0.3439
Kelvin probe (SKP) 5050 with a KP Technology. The value of ionization energy (IE) was obtained photoemission spectroscopy system in air (PESA) using Riken AC-2 system with a deuterium lamp and an energy scan from 4 to 6 eV with 0.05 eV steps. For electrical characterization Ni/Au contacts (120/80 nm) were deposited by e-beam at 10 6 vacuum pressure, using a shadow mask. Diode behaviour was studied using a probe station Cascade SUMMIT 11741B-HT and Keithley 4200 operated at mA, at the range from 3 to 3 V. 2.4. PIN diode fabrication Fig. 3 shows device structure for ITO/NiO/MAPbBr3/ZnO/Al diode. From down to up, ITO substrate, was used as bottom contact; followed by NiO film of 60 nm thick was deposited, chosen by it adherence with ITO, by pulsed laser deposition (PLD) at room temperature, with a carrier concentration of ~1017 cm 3 and resistivity of ~102 Ω-cm [39]; above, MAPbBr3 perovskite film of 3 μm was deposited; after that, ZnO film of 80 nm thick deposited by magnetron sputtering at room tem perature, with a carrier concentration of ~1019 cm 3 and resistivity of ~101 Ω-cm; and finally, Al film of 150 nm thick as top contact was deposited by shadow mask; 100 μm diameter aluminum electrodes on top surface of the diode was used for its characterization. 3. Results and discussions 3.1. Films structural study Fig. 4 shows X-rays diffraction patterns of MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7. It is possible to appreciate in all dif fractograms that correspond to perovskite cubic structure, with peaks at 14.83� , 21.13� , 30.06� , 33.73� , 37.12� , 43.08� , and 45.82� , at planes of (100), (110), (200), (210), (211), (220) and (300), respectively [40]. It is possible to appreciate that there are neither changes in the relative intensity nor shifting of the peaks, which is assumed to temperature and � pressure until 100 C and 5000 psi, respectively. Table 1 shows the crystallite size (D), microstrain, dislocation density which are calculated using the Popa model [41], and the lattice parameter by Nelson-Riley method from XRD analysis [42]. Annealing and pressure effect at S1–S7 does not produce any strain into the MAPbBr3 crystalline structure.
Fig. 5. MAPbBr3 perovskite films; a) Transmittance spectrum and b) Band gap at S1, S2, S3, S4, S5, S6 and S7.
Table 2 MAPbBr3 perovskite Fermi level at different conditions. Perovskite
Valence band (VB)
Conduction band (CB)
Work function (WF)
Fermi level (EFi)
S1 S2 S3 S4 S5 S6 S7
5.3249 5.3422 5.3136 5.3134 5.3089 5.2942 5.2707
3.0449 3.0622 3.0336 3.0334 3.0289 3.0142 2.9907
4.8 4.88 4.82 4.71 4.63 4.97 5
4.1849 4.2022 4.1736 4.1734 4.1689 4.1542 4.1307
3.2. Optical characterization Fig. 5 shows MAPbBr3 perovskite films; a) Transmittance spectrum and b) Band gap at S1, S2, S3, S4, S5, S6 and S7. In a) transmittance was similar, 2% in S1, S2 and S3. Transmittance for S4, S5, S6 and S7 were 10, 36, 52 and 55%, respectively. It can observed that transmittance increase when pressure is higher than 2000 until 5000 psi. Which could be assumed that film obtain a better microstructural distribution when pressure increase. In b) it is possible to appreciate that for all the films the band-gap was 2.28 eV [43,44]. Table 2 shows valence band (VB), conduction band (CB), work function (WF) and Fermi level (EFi), for MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7. Valence band and work function were obtained
Zeiss Supra 40, operated at 10 kV, while roughness was obtained by atomic force microscope (AFM) using a DM01 Veeco Dimension 5000 with 0.501 Hz scan rate. The optical characterization (transmittance, absorbance and Eg) were obtained from UV–Vis spectrum with a Stel larNet spectrometer in the 400–1050 nm wavelength range at room temperature. The work function (WF) was determinated by a scanning 3
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Materials Science in Semiconductor Processing 110 (2020) 104965
Fig. 6. SEM micrographs of MAPbBr3 perovskites films at S1, S2, S3, S4, S5, S6 and S7.
increasing, c) 0.538, d) 0.55, e) 0.588, f) 0.6 and g) 0.62 μm2. The increment of grain size from S3 to S7 could be due to the grains coalition and planarization effect by conglomerate grains due to films pressure, which allowed to increase their boundaries, it could be possible than films increase their conductivity. Fig. 7 shows AFM of MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7. It is possible to appreciate that roughness is similar in S1 and S2, 118 and 114 nm, respectively. but from S2 to S3 (56 nm), had a decrement significantly, it should be by pressure effect in the system, after that, roughness was decreasing gradually, in S4 (43 nm), S5 (30 nm), S6 (21 nm) and S7 (6 nm). Then, hot press system was effective for decrease roughness and apply high pressure had more planarization on the surface films and the best film was S7, because if roughness is low it has better conductivity properties with the film that is deposited on top. 3.4. Diode fabrication Fig. 8 shows diode configuration and energy level diagrams; a) ITO/ NiO/MAPbBr3/ZnO/Al and b) cross-sectional SEM image, where MAPbBr3 is the emitting layer, NiO and ZnO are used as the electron and hole injection layers, respectively. The valence band of the perovskite is 5.0 eV. ITO and Al, used as substrate and metal contact, respectively. In b), shows cross-sectional by SEM with a sandwich structure. The thickness of ITO, NiO, MAPbBr3, ZnO and Al are 140 nm, 60 nm, 3 μm, 80 nm and 150 nm, respectively. Fig. 9 shows J-V curves for ITO/NiO/MAPbBr3/ZnO/Al diode structure. It is seen good diode behaviour with more than 2 orders of magnitude between leakage and forward current in the diode. Its func tional range is from 3 to 3 V and leakage current is stable from 3 to 0. This result is better than previous report [45,46].
Fig. 7. AFM of MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7.
from PESA and SKP equipment, respectively. Conduction band was calculated with VB - band gap difference. Fermi level by VB and CB average. It can observed that EFi values, from 4.1307 to 4.2022, were lower than WF, 4.8–5 eV, and shows p-type character for all the films [45]. WF values are close to Ni and Au (5.03 and 5.1, respectively), which these materials can be used as ohmic contact for device fabrication. 3.3. Surface morphology and films roughness study
4. Conclusions
Fig. 6 shows SEM micrographs of MAPbBr3 perovskites films at S1, S2, S3, S4, S5, S6 and S7. It is possible to appreciate that from S1 to S2 increased average grain size, of 0.343–0.43 μm2, after that, to apply � pressure and same temperature (100 C), the grain size average continue
MAPbBr3 perovskite films 3 μm thick were succesfully deposited by two steps, PbBr2 and MABr by close space sublimation. 4
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Materials Science in Semiconductor Processing 110 (2020) 104965
Fig. 8. Diode configuration and energy level diagrams; a) ITO/NiO/MAPbBr3/ZnO/Al and b) cross-sectional SEM image.
CRediT authorship contribution statement �n G. Martínez-Falomir: Investigation, Data curation. C.A. Gibra Lopez-Lazcano: Investigation, Conceptualization, Visualization. J.L. �nchez: Supervision, Writing - review & editing. Almaral-Sa Acknowledgements This work was partially supported by CONACYT [scholarship #295770 and Mixed Scholarships Program (08/2017-07/2018)]; Uni �noma de Sinaloa-DGIP by project PROFAPI2015/011. We versidad Auto �pez, Ph.D. Iker Rodrigo are grateful to Ph.D. Manuel A. Quevedo Lo �vez Urbiola, Ph.D. María Isabel Pintor Monroy, Ph.D. Marissa Hig Cha gins, M.S. Bayron L. Murillo Borjas, and M.S. Martín Gregorio Reyes Banda from The University of Texas at Dallas. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.mssp.2020.104965.
Fig. 9. J–V curves for ITO/NiO/MAPbBr3/ZnO/Al diode structure.
Perovskite at S1, S2, S3, S4, S5, S6, and S7, did not caused any structural change (XRD). Band gap was 2.28 eV in all samples, it was no possible to observed any changes in each condition. The grain size incremented by using hot press system (SEM). Roughness decreased from 118 nm to 6 nm using the hot press sys � tem at 100 C-5000 psi (S7). It was possible to obtain an acceptable diode behaviour with more than 2 orders of magnitud in rectification using NiO and ZnO as p and n type, respectively. MAPbBr3 perovskite film could be used for future applications in radiation detector.
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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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6
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Materials Science in Semiconductor Processing journal homepage: http://www.elsevier.com/locate/mssp
Pressure effect on CH3NH3PbBr3 perovskite films deposited by close space sublimation for PIN diode and its possible application in radiation detector �nchez * Gibr�an G. Martínez-Falomir , C.A. Lopez-Lazcano , J.L. Almaral-Sa � Universidad Aut� onoma de Sinaloa, Fuente de Poseid� on y Prol., Angel Flores S/N, C.P.81223, Los Mochis, Sinaloa, Mexico
A R T I C L E I N F O
A B S T R A C T
Keywords: CSS Pressure effect MAPbBr3 perovskite Diode application
In this work, methylammonium lead bromide (CH3NH3PbBr3) perovskite films are deposited by close space sublimation (CSS), by two steps, the first layer is lead bromide (PbBr2) and the second is methylammonium � bromide (MABr). Pressure effect on the films, from 1000 psi to 5000 psi at 100 C temperature, was studied. Perovskite films were characterized by XRD, UV–Vis, SEM, AFM, PESA and Kelvin probe. The results show a cubic structure perovskite (XRD), band gap of 2.28 eV (UV–Vis), 3 μm thickness and uniform grain distribution (SEM), roughness reduction from 118 nm to 6 nm (AFM), valence band of 5.0 eV (PESA) and work function from 4.8 to 5 eV (Kelvin probe). These properties could allow to use as radiation detector diode.
1. Introduction A new generation of hybrid perovskite materials with ABX3 struc ture; where, A is an organic cation, such as methylammonium (MA), B is an inorganic cation (Pb), and X is a halogen anion (Br), have attracted the attention due to its several applications such as solar cells structures [1–14], transistors (200–500 nm thicknesses) [15] and light-emitting nanoparticles [16], hybrid crystals, as radiation detector for alphas particles [17], x-rays [18], or neutrons [19]. CH3NH3PbBr3 (MAPbBr3) perovskite has a direct band-gap of 2.18–2.3 eV, with a small difference between films and crystals [20,21], although could obtain modifications on morphology by manipulating thermal annealing [22], it has not been possible without changing its structure [23]. In this perovskite the inorganic cation is an important factor to determinate electronic properties when used for devices ap plications [24], wich is associated with electronic and magnetic prop erties in combination with thermal and mechanical stability [25]. MAPbBr3 perovskite mechanical properties at room temperature are well known, its elastic region for loads up to 5–6 mN, before reaching the plastic deformation zone. Roughness is an usual problem for thick films in electronic devices: if this value is higher than the subsequent layer a short-circuit may occur between them [26]. Spin coating and inverse temperature crystalization are traditional deposition methods have been used to obtain high quality perovskites [27–30], but unlike them, close space sublimation (CSS) technique has some advantage, because it allows to estimate the films optimal
deposition conditions, use high vacuum and ramps control at tempera ture and time [31], also it is possible to obtain thick films in micrometers scale, controlling parameters in: crucible and substrate (temperature and gap) and chamber (pressure, temperature and gas type) [32]. These characteristics make CSS better than similar techniques, such as: close-spaced vacuum sublimation (CSVS) [33], hot wall epitaxy (HWE) [34,35] and quasi-close volume (QCV) [36]. The neutron radiation as its name implies is a neutron particle, so the detection methods for this kind of radiation are by indirect methods, one of those, is by capturing the neutron with a conversion layer usually LiF or 10B [37]. When the neutron is captured by 10B produces a decay re action where alphas and Li ions are emitted, the most possible reaction produces α-particles with energy of 1.47 MeV. Therefore if the material it is capable to detect α-particles also it would detect neutrons. Then a film with a high thickness, in orders of micrometers (μm) will be capable to stop α-particles from the reaction between a neutron and 10B layer [38]. In this work, we deposited MAPbBr3 perovskite films by CSS, improving morphology surface with a hot press system, applying tem � perature (100 C) and pressure at 1.8, 13.7, 20.6, 27.5, and 34.4 MPa (1000, 2000, 3000, 4000 and 5000 psi) over an area of 0.000625 m2 (1 square inches), which it meant a stress on the surface of 1, 8, 12, 17, and 21 kN. The hot press effect on the perovskites decreased roughness from 118 nm to 6 nm and 3 μm thickness was obtained. MAPbBr3 perovskite film properties regardless to radiation sensi tivity and also the results of thickness and diode behaviour could be a
* Corresponding author. E-mail address: [email protected] (J.L. Almaral-S� anchez). https://doi.org/10.1016/j.mssp.2020.104965 Received 8 November 2019; Received in revised form 21 January 2020; Accepted 24 January 2020 Available online 5 February 2020 1369-8001/© 2020 Elsevier Ltd. All rights reserved.
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Materials Science in Semiconductor Processing 110 (2020) 104965
2.3. Characterization of MAPbBr3 The crystalline structure of the perovskite films were obtained by Xray diffraction (XRD) using a Rigaku Ultima III X-ray diffractometer, using Cu Kα radiation. All the data was obtained at the scan speed of 0.5� /min. After background subtraction, the intensity profile were expanded into WinJade program (Williamson-Hall method). The morphology was studied by scanning electron microscope (SEM) using a
Fig. 1. Schematic of the close space sublimation (CSS) chamber.
great support for future applications in radiation detector. 2. Experimental 2.1. Materials Lead bromide (PbBr2), 98þ % pure and methylammonium bromide (MABr) were purchased from Alfa Aesar and Luminescence Technology Corporation, respectively. 2.2. Deposition of MAPbBr3 perovskite films by close space sublimation (CSS)
Fig. 3. Device structure for ITO/NiO/MAPbBr3/ZnO/Al diode.
The CSS equipment has top (crucible) and down (substrate) heaters, both of them are used to control the temperature independently. The substrates were glass, glass/Au and ITO/NiO. Fig. 1 shows a schematic of the close space sublimation (CSS) chamber. The deposition of MAPbBr3 is achieved by the sequential deposition (two steps) of PbBr2 and MABr at 90 mTorr deposition pressure. Fig. 2 shows depositions parameters in a) the first step (PbBr2), with � error bars at 10 C, four temperatures ramps of 300 s each were applied simultaneously onto both, substrate (s) and crucible (c), to obtain the � � film. The first ramp was at 25 C, the second ramp was 200 C, and 175 � � � C, third and fourth ramp were 400 C and 225 C for substrate and crucible heater, respectively. Fig. 2 b) second step (MABr) onto the � PbBr2 film, facing up toward precursor, with error bars at 10 C. We programmed temperatures four ramps. From ramp one to three, 300 s for both (up and down) and fourth ramp, 4500 s. The same temperature for crucible and MABr film was applied in both, the first and second � � ramp, using 25 C and 100 C, respectively; third and fourth ramp were � � 100 C and 175 C, for crucible and MABr, respectively. The perovskite thickness can be controlled considering time, temperature and vacuum pressure into CSS chamber. MAPbBr3 perovskites films were applied at no anneal-no pressure � � (S1), 100 C-no pressure (S2), and by hot press system at 100 C-1000 psi � � � (S3), 100 C-2000 psi (S4), 100 C-3000 psi (S5), 100 C-4000 psi (S6) � � and 100 C-5000 psi (S7) by 3 h each, with 2 C of error bar.
Fig. 4. X-rays diffraction patterns of MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7.
Fig. 2. Depositions parameters to obtain a) PbBr2 and b) MABr. 2
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Materials Science in Semiconductor Processing 110 (2020) 104965
Table 1 Calculated values of crystallite size, microstrain, dislocation density and lattice parameter of MAPbBr3 at different conditions. 3
(nm 2)
No.
2θ (� )
β(� )
D (nm)
δ x 10
1 2 3 4 5 6 7
14.83635 21.13377 30.06349 33.7314 37.12903 43.08191 45.82614
0.34884 0.33859 0.30278 0.29638 0.29423 0.29106 0.2764
22.965663 23.8676167 27.1674339 28.0091483 28.4852288 29.343845 31.2041107
1.896016114 1.755423431 1.354886022 1.274677128 1.23242522 1.161357586 1.02701404
ε x10
3
11.69049764 7.919609543 4.919608452 4.265607071 3.822235754 3.217308476 2.853239225
� � Cos2 θ Cos2 θ þ 1=2 Sen θ θ 1.8570 1.2273 0.7726 0.6330 0.5353 0.3967 0.3439
Kelvin probe (SKP) 5050 with a KP Technology. The value of ionization energy (IE) was obtained photoemission spectroscopy system in air (PESA) using Riken AC-2 system with a deuterium lamp and an energy scan from 4 to 6 eV with 0.05 eV steps. For electrical characterization Ni/Au contacts (120/80 nm) were deposited by e-beam at 10 6 vacuum pressure, using a shadow mask. Diode behaviour was studied using a probe station Cascade SUMMIT 11741B-HT and Keithley 4200 operated at mA, at the range from 3 to 3 V. 2.4. PIN diode fabrication Fig. 3 shows device structure for ITO/NiO/MAPbBr3/ZnO/Al diode. From down to up, ITO substrate, was used as bottom contact; followed by NiO film of 60 nm thick was deposited, chosen by it adherence with ITO, by pulsed laser deposition (PLD) at room temperature, with a carrier concentration of ~1017 cm 3 and resistivity of ~102 Ω-cm [39]; above, MAPbBr3 perovskite film of 3 μm was deposited; after that, ZnO film of 80 nm thick deposited by magnetron sputtering at room tem perature, with a carrier concentration of ~1019 cm 3 and resistivity of ~101 Ω-cm; and finally, Al film of 150 nm thick as top contact was deposited by shadow mask; 100 μm diameter aluminum electrodes on top surface of the diode was used for its characterization. 3. Results and discussions 3.1. Films structural study Fig. 4 shows X-rays diffraction patterns of MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7. It is possible to appreciate in all dif fractograms that correspond to perovskite cubic structure, with peaks at 14.83� , 21.13� , 30.06� , 33.73� , 37.12� , 43.08� , and 45.82� , at planes of (100), (110), (200), (210), (211), (220) and (300), respectively [40]. It is possible to appreciate that there are neither changes in the relative intensity nor shifting of the peaks, which is assumed to temperature and � pressure until 100 C and 5000 psi, respectively. Table 1 shows the crystallite size (D), microstrain, dislocation density which are calculated using the Popa model [41], and the lattice parameter by Nelson-Riley method from XRD analysis [42]. Annealing and pressure effect at S1–S7 does not produce any strain into the MAPbBr3 crystalline structure.
Fig. 5. MAPbBr3 perovskite films; a) Transmittance spectrum and b) Band gap at S1, S2, S3, S4, S5, S6 and S7.
Table 2 MAPbBr3 perovskite Fermi level at different conditions. Perovskite
Valence band (VB)
Conduction band (CB)
Work function (WF)
Fermi level (EFi)
S1 S2 S3 S4 S5 S6 S7
5.3249 5.3422 5.3136 5.3134 5.3089 5.2942 5.2707
3.0449 3.0622 3.0336 3.0334 3.0289 3.0142 2.9907
4.8 4.88 4.82 4.71 4.63 4.97 5
4.1849 4.2022 4.1736 4.1734 4.1689 4.1542 4.1307
3.2. Optical characterization Fig. 5 shows MAPbBr3 perovskite films; a) Transmittance spectrum and b) Band gap at S1, S2, S3, S4, S5, S6 and S7. In a) transmittance was similar, 2% in S1, S2 and S3. Transmittance for S4, S5, S6 and S7 were 10, 36, 52 and 55%, respectively. It can observed that transmittance increase when pressure is higher than 2000 until 5000 psi. Which could be assumed that film obtain a better microstructural distribution when pressure increase. In b) it is possible to appreciate that for all the films the band-gap was 2.28 eV [43,44]. Table 2 shows valence band (VB), conduction band (CB), work function (WF) and Fermi level (EFi), for MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7. Valence band and work function were obtained
Zeiss Supra 40, operated at 10 kV, while roughness was obtained by atomic force microscope (AFM) using a DM01 Veeco Dimension 5000 with 0.501 Hz scan rate. The optical characterization (transmittance, absorbance and Eg) were obtained from UV–Vis spectrum with a Stel larNet spectrometer in the 400–1050 nm wavelength range at room temperature. The work function (WF) was determinated by a scanning 3
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Fig. 6. SEM micrographs of MAPbBr3 perovskites films at S1, S2, S3, S4, S5, S6 and S7.
increasing, c) 0.538, d) 0.55, e) 0.588, f) 0.6 and g) 0.62 μm2. The increment of grain size from S3 to S7 could be due to the grains coalition and planarization effect by conglomerate grains due to films pressure, which allowed to increase their boundaries, it could be possible than films increase their conductivity. Fig. 7 shows AFM of MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7. It is possible to appreciate that roughness is similar in S1 and S2, 118 and 114 nm, respectively. but from S2 to S3 (56 nm), had a decrement significantly, it should be by pressure effect in the system, after that, roughness was decreasing gradually, in S4 (43 nm), S5 (30 nm), S6 (21 nm) and S7 (6 nm). Then, hot press system was effective for decrease roughness and apply high pressure had more planarization on the surface films and the best film was S7, because if roughness is low it has better conductivity properties with the film that is deposited on top. 3.4. Diode fabrication Fig. 8 shows diode configuration and energy level diagrams; a) ITO/ NiO/MAPbBr3/ZnO/Al and b) cross-sectional SEM image, where MAPbBr3 is the emitting layer, NiO and ZnO are used as the electron and hole injection layers, respectively. The valence band of the perovskite is 5.0 eV. ITO and Al, used as substrate and metal contact, respectively. In b), shows cross-sectional by SEM with a sandwich structure. The thickness of ITO, NiO, MAPbBr3, ZnO and Al are 140 nm, 60 nm, 3 μm, 80 nm and 150 nm, respectively. Fig. 9 shows J-V curves for ITO/NiO/MAPbBr3/ZnO/Al diode structure. It is seen good diode behaviour with more than 2 orders of magnitude between leakage and forward current in the diode. Its func tional range is from 3 to 3 V and leakage current is stable from 3 to 0. This result is better than previous report [45,46].
Fig. 7. AFM of MAPbBr3 perovskite films at S1, S2, S3, S4, S5, S6 and S7.
from PESA and SKP equipment, respectively. Conduction band was calculated with VB - band gap difference. Fermi level by VB and CB average. It can observed that EFi values, from 4.1307 to 4.2022, were lower than WF, 4.8–5 eV, and shows p-type character for all the films [45]. WF values are close to Ni and Au (5.03 and 5.1, respectively), which these materials can be used as ohmic contact for device fabrication. 3.3. Surface morphology and films roughness study
4. Conclusions
Fig. 6 shows SEM micrographs of MAPbBr3 perovskites films at S1, S2, S3, S4, S5, S6 and S7. It is possible to appreciate that from S1 to S2 increased average grain size, of 0.343–0.43 μm2, after that, to apply � pressure and same temperature (100 C), the grain size average continue
MAPbBr3 perovskite films 3 μm thick were succesfully deposited by two steps, PbBr2 and MABr by close space sublimation. 4
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Materials Science in Semiconductor Processing 110 (2020) 104965
Fig. 8. Diode configuration and energy level diagrams; a) ITO/NiO/MAPbBr3/ZnO/Al and b) cross-sectional SEM image.
CRediT authorship contribution statement �n G. Martínez-Falomir: Investigation, Data curation. C.A. Gibra Lopez-Lazcano: Investigation, Conceptualization, Visualization. J.L. �nchez: Supervision, Writing - review & editing. Almaral-Sa Acknowledgements This work was partially supported by CONACYT [scholarship #295770 and Mixed Scholarships Program (08/2017-07/2018)]; Uni �noma de Sinaloa-DGIP by project PROFAPI2015/011. We versidad Auto �pez, Ph.D. Iker Rodrigo are grateful to Ph.D. Manuel A. Quevedo Lo �vez Urbiola, Ph.D. María Isabel Pintor Monroy, Ph.D. Marissa Hig Cha gins, M.S. Bayron L. Murillo Borjas, and M.S. Martín Gregorio Reyes Banda from The University of Texas at Dallas. Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.mssp.2020.104965.
Fig. 9. J–V curves for ITO/NiO/MAPbBr3/ZnO/Al diode structure.
Perovskite at S1, S2, S3, S4, S5, S6, and S7, did not caused any structural change (XRD). Band gap was 2.28 eV in all samples, it was no possible to observed any changes in each condition. The grain size incremented by using hot press system (SEM). Roughness decreased from 118 nm to 6 nm using the hot press sys � tem at 100 C-5000 psi (S7). It was possible to obtain an acceptable diode behaviour with more than 2 orders of magnitud in rectification using NiO and ZnO as p and n type, respectively. MAPbBr3 perovskite film could be used for future applications in radiation detector.
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Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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