The Effect of Titanium Oxide Substrate on the Film Morphology and Photoluminescence Properties of Organometal Halide Per
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The Effect of Titanium Oxide Substrate on the Film Morphology and Photoluminescence Properties of Organometal Halide Perovskites Zhihua Xu and Zhengtao Chen Department of Chemical Engineering, University of Minnesota-Duluth, Duluth, MN 55812, U.S.A. ABSTRACT We have investigated the film morphology and photoluminescence properties of spincoated CH3NH3PbI3-xClx films on mesoporous and compact TiO2 substrates. We observe that the perovskite film deposited on the mesoporous substrate composed of 20 nm TiO2 nanopaticles exhibits relatively uniform grain size, while the films deposited on the compact TiO2 substrate and the mesoporous substrate with large TiO2 nanoparticles (200 nm) show highly heterogeneous film morphology. The heterogeneity of film morphology has significant effect on the photoluminescence spectra and lifetime of the perovskite films. The result of time-resolved confocal microscopy unveils the relation between film structure and photoluminescence properties. INTRODUCTION Perovskite solar cells (PSCs) that utilize organometal halides as light absorber have been showing very impressive development in the past few years, with power conversion efficiency approaching 20%.[1-5] The representative Methylammonium Lead Iodide (CH3NH3PbI3) hybrid perovskites have demonstrated the desired characteristics such as broad light absorption, tunable band gap, excellent charge mobility and low-temperature solution processing, for the next generation low-cost photovoltaics. The organic-inorganic hybrid perovskites are intrinsically complex materials, and the film morphology of solution-casted perovskites is highly inhomogeneous. As a result, the device performance varies drastically with the deposition conditions such as moisture level and annealing temperature.[6] A deep understanding of the relationship of film morphology, optoelectronic properties and energy conversion processes of the hybrid perovskite is of critical importance for further improvement of the device performance. The perovskite solar cells can be fabricated with either a mesoporous or a planar device structure. In a mesoporous PV cell, the perovskite is deposited on a mesoporous metal oxide (such as TiO2 and Al2O3) nanoparticle layer that requires heat treatment at moderate high temperature;[3] While in the planar device structure, the perovskites is deposited on a compact metal oxide film which can be processed at low temperature.[2] Therefore, the planar structure seems to have the obvious advantage in terms of low temperature processing and simple fabrication over the mesoporous structure, although high power conversion efficiencies have been achieved with both structures. In this paper, we study the effect of mesoporous and compact titanium oxide substrates on the film morphology and photoluminescence (PL) properties of organometal halide perovskites with the aim to gain better understand the relationship of film morphology, optical properties and energy conversion processes inside the two different device structures.
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EXPERIMENTAL METHODS Mes
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