Regulating the Hydrolysis of TiCl ₄ during the Chemical Bath Deposition of TiO ₂ Electron Transport Layer for High‐Performance Carbon‐Based CsPbI ₃ Perovskite Solar Cells

Abstract TiO ₂ is widely utilized as an electron transport layer (ETL) in perovskite solar cells (PSCs) due to its suitable band structure, facile fabrication process, and high‐temperature stability. Compared to the other methods, the chemical bath deposition (CBD) method enables the preparation of uniform TiO ₂ films under low‐temperature conditions. However, during the deposition process, vigorous hydrolysis reactions and reactive intermediates lead to the formation of large agglomerated particles and oxygen vacancies, resulting in poor TiO ₂ ETL and low‐performance devices. Herein, sulfanilamide (SA) is introduced into the CBD solution to smoothen the hydrolysis reactions of TiCl ₄ during the CBD processes. The ─SO ₂ NH ₂ group of SA molecules renders the hydrolysis process more stable through coordination with titanium ions. The TiO ₂ films prepared using this method exhibit lower defect state densities and optimized energy band structures. As a result, the PCE of the carbon‐based CsPbI ₃ PSCs without a hole transport layer fabricated based on this strategy increases from 17.66% to 19.03%.