Energetics and Surface Photovoltage of Perovskites for Thin Film Photovoltaics
Iain Hamilton a, Matyas Daboczi a, Iain Baikie b, Ji-Seon Kim a
a Department of Chemistry and Centre for Plastic Electronics, Imperial College London, South Kensington Campus, London, United Kingdom
b KP Technology, Burn Street, Wick, Caithness, KW1 5EH, UK
NIPHO
Proceedings of International Conference on Perovskite Thin Film Photovoltaics, Photonics and Optoelectronics (ABXPV18PEROPTO)
Perovskite Thin Film Photovoltaics (ABXPV18). 27-28 Feb
Rennes, France, 2018 February 27th - March 1st
Organizer: Jacky Even
Oral, Ji-Seon Kim, presentation 080
DOI: https://doi.org/10.29363/nanoge.abxpvperopto.2018.080
Publication date: 11th December 2017

Continuous increase in the device performance of lead halide perovskite-based solar cells is strongly related to better understanding of optical and electronic properties of the perovskite layer. There are still many electronic processes in perovskites that are critical to device performance (e.g. ionic movement, charge carrier recombination, trapping of electrons and holes) and are not yet fully understood. Here we report our recent results of mixed-halide lead perovskites (MAPBr3-xIx) in terms of their energy levels and especially the illumination generated surface photovoltage (SPV) and its transient behaviour.

First, dark work function measurements show that the Fermi level of mixed halides increases with bromide content. We further show the work function of the perovskites used are significantly influenced by the substrate and the mixed halide perovskite films are intrinsically p-type semiconductors. Ambient pressure air photoemission spectroscopy shows that the HOMO values for the samples are mainly governed by MAPI3 domains (~5.3 eV), with the only significant increase in HOMO energy is for MAPBr3 (~5.6 eV), implying a variation in p-doping with halide composition.

Second, SPV transient measurements of mixed halide perovskite films show at least two distinctive processes taking place at different time scales, which are attributed to the generation/recombination of charge carriers and ionic migration. The magnitude (and direction) of each process depends upon both halide composition of the perovskite and the substrate used. We will discuss the impact of these findings on device performance.

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