The Impact of Lead Iodide on the Recombination Kinetics in Metal Halide Perovskite Films
Aboma Merdasa a, Alexandros Kiligaridis b, Carolin Rehermann a, Mojtaba Abdi-Jalebi c, Jonas Stöber a, Boris Louis a, Marina Gerhard a, Samuel D. Stranks c, Eva L. Unger a b, Ivan G. Scheblykin b
a Young Investigator Group, Hybrid Materials Formation and Scaling, Helmholtz-Zentrum Berlin, Albert-Einstein-Straße, 16, Berlin, Germany
b Department of Chemical Physics and NanoLund, Lund University, 22100 Lund, Sweden
c Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
nanoGe Perovskite Conferences
Proceedings of nanoGe International Conference on Perovskite Solar Cells, Photonics and Optoelectronics (NIPHO19)
International Conference on Perovskite Thin Film Photovoltaics
Jerusalem, Israel, 2019 February 24th - 27th
Organizers: Lioz Etgar and Kai Zhu
Oral, Aboma Merdasa, presentation 035
Publication date: 21st November 2018

Metal halide perovskites have rapidly become important semiconductor materials for photovoltaic devices. Despite solar cell efficiencies soaring over 20% [1], there are still aspects in regard to understanding the fundamental operational properties that are lacking. One active debate surrounds the influence of lead iodide (PbI2) on device performance as well as fundamental properties of the perovskite absorber [2].  Both beneficial and detrimental traits have been reported, where the ambiguity may not only be related to the amount of residual PbI2, but also to the distribution within the metal halide perovskite absorber layer and whether it is introduced during preparation or created by degradation [3]. Herein, we present a study on the impact of lead iodide on the charge-carrier recombination kinetics. We compare both the case of a vapor-deposited PbI2 layer on top of a methylammonium lead triiodide (MAPbI3) thin film as well as PbI2 generated as a result of photo-induced degradation during several hours of light-soaking under solar illumination conditions. By simultaneously acquiring spectrally-resolved photoluminescence quantum yield and time-resolved photoluminescence lifetime at excitation wavelengths ranging from 450 nm to 780 nm, we identify a unique radiative recombination mechanism occurring at the PbI2/MAPbI3 interface (disordered MAPbI3 region) when charge carriers are generated in PbI2. While PbI2 reportedly acts as a UV-filter,[4] we here demonstrate that charge carriers may in fact funnel via PbI2 and recombine in the perovskite. We thereby provide important insight into the long-debated question of whether excess PbI2 is beneficial or detrimental for charge carrier dynamics in perovskite solar absorber materials.

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