Synergistic Passivation for Efficient Inverted Inorganic Perovskite Solar Cells

Abstract Inorganic perovskites possess a bandgap compatible with silicon for tandem solar cells without excessive halide doping, and they also exhibit excellent thermal stability. However, interfacial defects and energy losses caused by energy level mismatch hinder the development of efficient inverted inorganic perovskite solar cells (PSCs). To address this issue, a multifunctional small molecule, S‐(2‐aminoethyl) isothiouronium bromide hydrobromide (SPD), which simultaneously achieves chemical and field passivation at the CsPbI_2.85Br_0.15/electron transport layer (PVK/ETL) interface. SPD contains electron‐donating amino groups (AG) and thiocarbonyl group (TG), enabling strong coordination with undercoordinated Pb²⁺ ions for chemical passivation. In parallel, the cation in this molecule exhibits a significant dipole moment, which modulates the interfacial electric field distribution and thereby suppresses carrier recombination at the interface. Incorporation of SPD at the perovskite surface significantly reduces nonradiative recombination, suppresses hysteresis, and improves carrier extraction. The SPD‐modified inorganic PSCs achieve a champion power conversion efficiency (PCE) of 21.15% with a voltage of 1.268 V, reducing the open‐circuit voltage (V_OC) loss to 452 mV. Unencapsulated devices retain 82.13% efficiency under 65 °C thermal aging for 600 h and maintain 92.54% of their initial efficiency after 200 h of continuous illumination.