The impact of surface chemistry in SnO2 on charge transport of lead halide perovskite solar cells

Abstract

Organic-inorganic lead halide perovskites have high power conversion efficiency and intriguing physical-chemical aspects that attract attention of the photovoltaic community. Methylammonium lead iodide (MAPI) is an archetypal material for lead halide perovskites and mixed electronic and ionic conductor. In order to investigate the key features of its performance, we have to consider the electronic transport as well as ionic transport properties. In previous study about perovskite interface, ions are responsible for the equilibrium space charge potential due to ion adsorption at the contact area between MAPI and oxide layers. The surface chemistry of oxide (TiO2 and Al2O3) and its interaction with perovskite plays an important role in charge transport in perovskite solar cells. From the perovskite solar cell structure, TiO2 electron transport layer is being replaced by SnO2 because of its excellent electrical and optical properties and low-temperature process. Nevertheless, the interfacial effect on charge transport between SnO2 and MAPI is not well identified. In this study, we investigate the surface chemistry of oxides (SnO2 and TiO2) and interface effects between MAPI and oxide layers. We also observed the interaction between SnO2 and MAPI by using UV-Vis spectroscopy, ICP, XPS and compared it with TiO2. Additionally, we measured the conductivity to understand the charge transport properties by controlling the contact area of MAPI and SnO2 interface. To optimize the charge transfer in SnO2 based solar cell, a comparison between compact SnO2 layer (prepared by ALD) and composite layer (prepared by spin coating) by using various measurements including external quantum efficiency (EQE) and photoluminescence (PL) was also provided. These physical and optical properties were extended to perovskite solar cells which give us evidence on charge extraction and recombination. Our work will provide a better physical understanding of the perovskite solar cell system.