Iminodiacetic Acid-Modified TiO2 Electron Transport Layers for Efficient and Stable CsPbI3−xBrx Perovskite Solar Cells

The efficiency of perovskite solar cells (PSCs) is mainly determined by their electron transport layer (ETL). In this work, we present a facile and efficient strategy to incorporate iminodiacetic acid (IDA) as a cost-effective, multifunctional dopant into hydrothermally synthesized TiO2 ETLs. This modification enables holistic defect passivation in the bulk TiO2, on its surface, and at the TiO2/perovskite interface, thereby significantly improving device performance. In particular, the dicarboxyl groups (-COOH) of the IDA molecule coordinate with Ti ions and oxygen vacancies at the TiO2 surface, effectively passivate the deep level traps, and improve the carrier (electron) mobility. At the same time, the imino groups (-NH-) assist in forming a thick and highly crystalline CsPbI3−xBrx perovskite film by coordinating to free Pb2+. Consequently, the best-performing device (5 mg/mL IDA) achieves a peak PCE of 12.16%, representing a relative enhancement of 38.9% compared to the control device (8.78%). The modified devices show significantly lower hysteresis (from 0.172 to 0.055) and better stability with more than 82% retention in the original performance after being stored in ambient air (25–30 °C, 20–30% RH) for 60 days. The present study offers a low-cost and industrially compatible technological pathway to produce efficient inorganic PSCs through molecular interfacial engineering.