Vacuum evaporated MA-free perovskites and post-annealing influences
Ran Ji a, Zongbao Zhang a, Martin Kroll a, Frederik Nehm a, Karl Leo a
a Institut für Angewandte Photophysik (IAPP)
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics and Perovskite Photonics and Optoelectronics (NIPHO20)
Sevilla, Spain, 2020 February 23rd - 25th
Organizer: Hernán Míguez
Poster, Ran Ji, 019
Publication date: 25th November 2019

Perovskites denoted by ABX3 structure (A = methylammonium (MA), formamidinium (FA), Cs, Rb; B = Pb, Sn; X = Cl, Br, I) have progressed rapidly in the past few years with power conversion efficiencies of their respective solar cells now at 25.2%. Currently, high-performance perovskite photovoltaics always incorporate MA, which is difficult to deposit via thermal evaporation, because of its precursor’s (MAI) high vapor pressure. Furthermore, MA is proven to cause stability issues, making it a risk factor for long-term stability and reproducibility that should be avoided. Industrial exploitation of perovskite technology is only feasible if high performance perovskite devices can be made without this major cause of instability.

Here, MA-free perovskites (FA1-xCsxPbI3-xBrx) are deposited using triple-source co-evaporation. The mechanism of post-annealing after thermal evaporation is investigated, showing an improvement of crystallinity for all tested conditions. However, device efficiencies still strongly depend on the stoichiometric ratio of FA, Cs, and Pb. Using the post-annealing process, the champion cell shows 15.1% efficiency, which is the highest reported value for evaporated MA-free perovskite solar cells, until now.

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