Elimination of Light-Induced Degradation at the Nickel Oxide-Perovskite Heterojunction towards Long-Term Operationally Stable Inverted Perovskite Solar Cells
Tianhao Wu a, Yabing Qi a
a Energy Materials and Surface Sciences Unit (EMSSU), Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1 Tancha, Onna-son, Kunigami-gun, Okinawa 904-0495, Japan
Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics
Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP23)
Kobe, Japan, 2023 January 22nd - 24th
Organizers: Seigo Ito, Hideo Ohkita and Atsushi Wakamiya
Oral, Tianhao Wu, presentation 011
DOI: https://doi.org/10.29363/nanoge.iperop.2023.011
Publication date: 21st November 2022

The inverted p-i-n structured perovskite solar cells (PSCs) using the charge-selective contacts with less sensitivity to ambient condition is regarded as a viable route to fabricate high-performance PSCs with better environmental stability, and nickel oxide (NiOx) is the most frequently used hole-selective contact at the illumination side due to its high carrier mobility, low cost, and high transparency. However, the lifetime of NiOx-based inverted PSCs is still relatively short (around 1000 hours), and further enhancement of their long-term operational stability is largely limited by the light-induced degradation at the NiOx-perovskite heterojunction. In this regard, a simple strategy based on construction of a stable buffer layer that can synergistically eliminate the light-induced degradation and minimize the charge recombination loss in NiOx-based inverted PSCs is highly desirable, and the development of in-situ characterization techniques are urgently needed to identify the degradation products and further clarify the degradation mechanism. In this work, we used time-resolved quadrupole mass spectrometry (MS) technique to reveal the degradation mechanism of NiOx-FAMAPbI3  (formamidinium-methylammonium iodide) perovskite heterojunction under operational condition: 1) generation of iodine vapor and free proton via the oxidation and deprotonation reactions; 2) formation of volatile products under elevated temperature, including hydrogen cyanide, methyliodide, and ammonia; 3) formation of condensation product, N-methyl formamidine, with the increased vapor pressures of dissociated FA and MA molecules. Inspired by the aprotic nature, good phototability, suitable size of trimethylsulfonium (TMS+), and the high oxidation potential of Br-, we introduced a novel TMSBr buffer layer between NiOx and perovskite to eliminate these multi-step photochemical reactions. Consequently, the TMSBr-stabilized inverted PSCs (1.53-eV bandgap) exhibited a promising efficiency of 22.1% with an open-circuit voltage of 1.18 V, and could retain approximately 82.8% of the initial efficiency after 2000-hour operation under AM1.5G light illumination, which translates into an estimated T80 lifetime of 2310 hours (the time over which the efficiency reduces to 80% of its initial value), which is among the highest operational lifetimes reported for NiOx-based PSCs.

This work was supported by funding from the Energy Materials and Surface Sciences Unit of the Okinawa Institute of Science and Technology Graduate University, the OIST R&D Cluster Research Program, the OIST Proof of Concept (POC) Program, and JST A-STEP Grant Number JPMJTM20HS, Japan. We thank the OIST Micro/Nanofabrication Section and Imaging Section for the support. Prof. L. H. thanks the National Natural Science Foundation of China (12074245 and U21A20171) and the JSPS KAKENHI Grant (21H02040).

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