Suppressing Phase Segregation in Wide Bandgap Perovskites for Monolithic Perovskite/Organic Tandem Solar Cells with Reduced Voltage Loss.

Abstract

Wide bandgap (WBG) perovskites through tuning iodine/bromine ratios are capable of merging with narrow bandgap organic bulk heterojunctions to construct tandem solar cells to overcome the Shockley-Queisser limitation. However, WBG perovskites readily suffer from light-induced halide ion migration, leading to detrimental phase segregation and hence severe open-circuit voltage (VOC ) loss. Here, to solve this issue, lead thiocyanate (Pb(SCN)2 ) and 2-thiopheneethylammonium chloride (TEACl) are synergistically employed to passivate and stabilize WBG perovskites with 1.79eV bandgap. It is demonstrated that the synergetic employment of Pb(SCN)2 and TEACl suppresses light-induced phase segregation, passivates WBG perovskite defects, and reduces non-radiative recombination, hence alleviating VOC loss. As a result, optimized WBG perovskite solar cells (PSCs) are obtained with an impressive VOC of 1.26V and power conversion efficiency (PCE) over 17.0%. Furthermore, the interconnection layer is optimized to minimize the VOC loss and construct two-terminal perovskite/organic tandem solar cells with a narrow bandgap organic blend bulk heterojunction of PM6:Y6 and achieve a champion PCE of 22.29% with a high VOC of 2.072V. In addition, these tandem solar cells maintain 81% of their initial efficiency after 1000h continuous tracking at the maximum power point (MPP) under 100 mW cm-2 white light illumination.