Regulating the Hydrolysis of TiCl4 during the Chemical Bath Deposition of TiO2 Electron Transport Layer for High-Performance Carbon-Based CsPbI3 Perovskite Solar Cells

Abstract

TiO₂ 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 TiO₂ 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 TiO₂ ETL and low-performance devices. Herein, sulfanilamide (SA) is introduced into the CBD solution to smoothen the hydrolysis reactions of TiCl₄ during the CBD processes. The ─SO₂NH₂ group of SA molecules renders the hydrolysis process more stable through coordination with titanium ions. The TiO₂ films prepared using this method exhibit lower defect state densities and optimized energy band structures. As a result, the PCE of the carbon-based CsPbI₃ PSCs without a hole transport layer fabricated based on this strategy increases from 17.66% to 19.03%.