Synthesis and Characterization of Halide Hybrid Perovskites Thin Films by Sequential Physical Vapor Deposition
Juvet Nche Fru a, Nolwazi Nombona b, Mmantsae Diale a
a University of Pretoria, South Africa, Hatfield, Pretoria, 28, Pretoria, South Africa
b University of Pretoria, South Africa, Hatfield, Pretoria, 28, Pretoria, South Africa
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics and Perovskite Photonics and Optoelectronics (NIPHO20)
Sevilla, Spain, 2020 February 23rd - 25th
Organizer: Hernán Míguez
Poster, Juvet Nche Fru, 024
Publication date: 25th November 2019

In this study, lead iodide (PbI2)-rich halide hybrid (HH) methylammonium lead bromide/iodide (MAPb(I1-xBrx)3) thin films were synthesized by stacking methylammonium lead tri-bromide (MAPbBr3) on methylammonium lead tri-iodide (MAPbI3), both grown by sequential physical vapor deposition. The structural, optical, morphological and electrical properties of the HH thin films were studied as the thickness of methylammonium bromide (MABr) was increased from 300 to 500 nm. The X-ray diffractograms confirmed transformation from tetragonal MAPbI3  to the cubic MAPbBr3 structure as previously observed by Pistor et al. [1], where MAPb(I1-xBrx)3 (x= 0.89 - 0.95) is formed together with PbI2 phase. UV-Vis absorption spectra showed that the band gaps of the HH thin films decreased from 2.21 to 2.14 eV as the thickness of MABr was increased. Scanning electron microscopy micrographs depicted densely packed pinhole-free grains which fully covered the substrate. The average grain size increased from 150 to 320 nm as the thickness of MABr was increased. Electrical properties showed that the carrier mobilities increased linearly from 3.00 x 10-3 to 1.62 cm2 V-1 s-1 while the trap density decreased from 5.06 x 1015 to 1.29 x 1015 cm-3 as thickness of MABr was increased, using the space charge limited current theory. Analysis of dark current density-voltage curves of the hole-transport-layer-free mesoporous solar cells (FTO/c-TiO2/m-TiO2/MAPb(I1-xBrx)3), containing 500 nm thick MABr, revealed high built-in voltage (1.6 V) and ideality factor of 1.5, using the thermionic emission model. This study introduces a simple way of growing HH perovskites thin films for hole-transport-layer-free solar cells.

The authors wish to thank the University of Pretoria, NRF-TWAS and NRF grant no N01156/115463 of the SARChI for financial support.

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