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 ( V OC ) 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 1.79 eV 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 V OC loss. As a result, optimized WBG perovskite solar cells (PSCs) are obtained with an impressive V OC of 1.26 V and power conversion efficiency (PCE) over 17.0%. Furthermore, the interconnection layer is optimized to minimize the V OC 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 V OC of 2.072 V. In addition, these tandem solar cells maintain 81% of their initial efficiency after 1000 h continuous tracking at the maximum power point (MPP) under 100 mW cm −2 white light illumination.