The Impact of Spiro-OMeTAD Photodoping on the Reversible Light-Induced Transients of Perovskite Solar Cells
Sonia Ruiz Raga a b, Boer Tan a, Kevin Rietwyk a, Jianfeng Lu a c, Sebastian Fürer a, Udo Bach a d e, Yibing Cheng c f
a ARC Centre of Excellence in Exciton Science, Department of Chemical Engineering, Monash University, Clayton, VIC, Australia
b Institut Català de Nanociència i Nanotecnologia (ICN2), Edifici ICN2, Campus UAB, Cerdanyola del Valles, Spain
c State Key Laboratory of Silicate Materials for Architecture, Wuhan University of Technology, 122 Luoshi Rd, Wuhan, 430070, China
d CSIRO Manufacturing, Clayton, Australia, Clayton VIC 3168, Australia, Clayton, Australia
e Melbourne Centre for Nanofabrication, Australia, Australia
f Monash University, Department of Materials Science and Engineering, AU, Alliance Lane, 22, Clayton, Australia
Proceedings of International Conference on Impedance Spectroscopy and Related Techniques in Metal Halide Perovskites (PERIMPED)
Online, Spain, 2020 October 6th - 7th
Organizers: Juan Bisquert, Bruno Ehrler and Eline Hutter
Poster, Sonia Ruiz Raga, 025
Publication date: 25th September 2020

Hole transporting materials (HTMs) play essential roles in facilitating hole extraction and suppressing recombination in lead halide perovskite solar cells (PSCs). High levels of p-doping in HTMs is necessary for achieving high device performance, attributed to an increased electrical conductivity. In this work, we provide evidences that the poor performance of PSCs with low levels of doping (i.e., 4 mol% spiro-OMeTAD+ ) in spiro-OMeTAD is mainly caused by the presence of a Schottky barrier at the perovskite/spiro-OMeTAD interface, hampering hole injection. Under continuous illumination at open-circuit condition, the barrier gradually diminishes, increasing the PSC power conversion efficiency by 70-fold after 7 hours. This process is completely reversible, returning to the initial poor performance after dark storage. We attribute this improvement in performance to a gradual photodoping of spiro-OMeTAD, triggered by the transfer of photogenerated holes and mediated by the slow migration of halide anions from perovskite to compensate the newly formed spiro-OMeTAD+ . In-situ parallel Manuscript Click here to view linked References analyses with impedance spectroscopy (IS) and photoluminescence are employed to gain insights into the charge dynamics along with light soaking. We find that the Schottky barrier resistance overlays with the recombination signal at the high frequency arc of IS, having important implications for the IS data analysis for PSCs. The work elucidates a major mechanism causing the slow efficiency variations during light/dark cycling, commonly observed in PSCs, which complicates the determination of long-term stability.

The authors are grateful for the financial support by the Australian Research Council (ARC) discovery project (DP160104575), the Australian Centre for Advanced Photovoltaics (ACAP), the Australian Renewable Energy Agency and the ARC Centre of Excellence in Exciton Science (ACEx: CE170100026). The authors would like to thank Dr. Bertoluzzi for the discussions and support for the band diagrams

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