Formamidium-Based Quasi-2D Dion Jacobson Perovskites for Efficient and Durable Wide Band Gap Solar Cells

In the last decade, three-dimensional (3D) metal halide perovskite solar cells have displayed tremendous progress in photoconversion efficiencies. The tunable bandgaps enable mixed halide perovskite compositions to be used as the wide bandgap (WB) sub-cell in perovskite-perovskite tandems. However, halide segregation and ion migration under photo-illumination create bandgap instability that limits the long-term durability of these wideband gap subcells. Quasi-2D halide perovskites, on the other hand, have demonstrated better durability against moisture and photo illumination due to their large organic cations but still lag in efficiency due to large exciton binding energies creating charge extraction barriers. Here, we synthesize Formamidinium (FA+) based 2D Dion Jacobson (DJ) perovskite with a band gap of 1.8eV, which is ideally suited for building bottom cells for perovskite-perovskite and perovskite/Si tandems. Films fabricated using the phase-selective memory seeds process preserved the phase purity of the n=3 2D perovskite¹. More importantly, FA 2D DJ perovskite films demonstrate 2x more stability against the triple-cation 3D perovskite films in heat and 85% humidity. These properties make FA 2D DJ perovskites promising candidates for wide bandgap subcells in perovskite-perovskite tandem.<br/><br/>(1) Sidhik, S.; Li, W.; Samani, M. H. K.; Zhang, H.; Wang, Y.; Hoffman, J.; Fehr, A. K.; Wong, M. S.; Katan, C.; Even, J.; Marciel, A. B.; Kanatzidis, M. G.; Blancon, J.-C.; Mohite, A. D. Memory Seeds Enable High Structural Phase Purity in 2D Perovskite Films for High-Efficiency Devices. <i>Advanced Materials</i> <b>2021</b>, <i>33</i> (29), 2007176. https://doi.org/10.1002/adma.202007176.