Cold Thoughts on Perovskite Fever

TLDR: In this paper, the authors showed that nickel, as an industrial commodity metal with work function of 5.1 eV, can replace gold as the back cathode in perovskite solar cells.

Abstract: The latest progress in solution process-based organic-inorganic hybrid perovskites solar cells is reshaping the growth pattern of any previous photovoltaic technologies and has raised a storm of research fever. However, despite the success in boosting efficiency, it also appears high time to inject an intense dose of cold thoughts into this globally-spreading “perovskite fever”, because perovskite solar cells are still facing several critical challenges. Prominently, these hybrid perovskites suffer from the materials instability in moisture, the use of environment-hazardous lead, the costly and unstable complex organics as hole transport materials, the use of precious metals as back cathode, the hysteresis in current-voltage scans, the tricky engineering of good-quality perovskite films. Moreover, there are still some missing puzzle pieces for a comprehensive basic science understanding. In this talk, I will present our work on tackling these challenges. First, that nickel, as an industrial commodity metal with work function of 5.1 eV, can replace gold as the back cathode in perovskite solar cells. Furthermore, when partial iodides in CH3NH3PbI3 are replaced with pseudohalide ions thiocyanate (SCN-), the resulting SCN-containing perovskite films strikingly rival the conventional CH3NH3PbI3 films in terms of moisture, and exhibit efficiency comparable to that of CH3NH3PbI3-based cells fabricated in the same way. In addition the unusual electron-rotor interaction discovered in hybrid perovskite materials using isotope effects and the unusual optical and electronic properties of hybrid perovskite crystals under high pressure. These fundamental studies provide a new coordination in the mechanistic foundation needed for better materials by designing.

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Table 2 | Polaron trapping energy [meV] for electron and hole with different C-N pointing directions Crystallogra