Buried Interface Modification Toward Efficient CsPbI_2.2Br_0.8 Based Monolithic Perovskite/Organic Tandem Solar Cells

Wide-bandgap perovskite sub-cells (WPSCs), one of the most crucial components of perovskite-based tandem solar cells (PTSCs), play a critical role in determining the performance of tandem devices. However, confined by the compromised crystallization properties of wide-bandgap perovskites, WPSCs exhibit significantly lower efficiency than their theoretical limit. In particular, for n-i-p structured all-inorganic WPSCs (AIWPSCs), severe nonradiative recombination due to the buried interface defects severely decreases the photovoltaic performance. Herein, an efficient propionate group (PA^-) based ionic liquid, methylamine propionate (MAPA), is introduced into the perovskite/electron-transport layer (ETL) interface to passivate the buried interface of AIWPSCs. The intense interaction between the PA^- and Pb-Pb dimer effectively heals the defects at the buried interface and facilitates a more homogeneous elemental distribution in the perovskite film. As a result, CsPbI_2.2Br_0.8-based AIWPSCs with a high power conversion efficiency (PCE) of 18.29% and open-circuit voltage (V_OC) of 1.33 V are obtained, which illustrates the superiority of MAPA in optimizing the performance of AIWPSCs. Moreover, by integrating these AIWPSCs with small-bandgap organic solar cells (SOSCs), high performance n-i-p structured all-inorganic perovskite/organic tandem solar cells (AIPOTSCs) with a high PCE of 23.19% and V_OC of 2.08 V are also achieved.