Synergistic defect passivation and crystallization control via bifunctional ethylenethiourea additive in CsPbIBr2 perovskite solar cells

All-inorganic CsPbIBr 2 perovskite is a promising light-harvesting material due to its greater thermal stability compared to organic–inorganic hybrid perovskites. However, low film quality, high defect density, and poor crystallization hinder charge transport and cause non-radiative recombination in CsPbIBr 2 -based perovskite solar cells (PSCs). In this work, ethylenethiourea (ETU), a bifunctional Lewis-base S–donor additive, was introduced to synergistically regulate crystallization kinetics and passivate uncoordinated Pb 2+ defects in CsPbIBr 2 films. The optimized carbon-based PSC incorporating 2.5 mg mL −1 ETU reached a power conversion efficiency (PCE) of 6.67%, a 60% improvement over the 4.25% of the pristine device, primarily driven by improved film morphology, suppressed trap-assisted recombination, and enhanced charge transport. Furthermore, the unencapsulated ETU-CsPbIBr 2 device sustained better long-term stability by retaining over 90% of its initial PCE after 1000 h of storage under ambient conditions (25 °C, 25% RH) and after 120 h of aging at 85 °C in an N 2 environment. This work demonstrates that additive engineering using ETU is an effective strategy to control crystallization and passivate defects, thereby providing an effective route to manufacture efficient and robust carbon-based all-inorganic PSCs.