Crystallization modulation through optimized SnO2 ETL enables over 20% efficiency in HTM-free carbon electrode perovskite solar cells

Tin dioxide (SnO2) is the most widely used electron transport layer (ETL) in perovskite solar cells (PSCs), and its characteristics play a crucial role in both perovskite crystallization and device performance. In this study, phenazine (PZ) is employed to disperse SnO2 nanoparticles for optimizing solution-processed SnO2 ETLs while regulating the crystallization kinetics of perovskites. Experimental results demonstrate that the SnO2-PZ ETL exhibits better surface flatness, lower defect state density, and a more matched band structure. Moreover, the SnO2-PZ ETL provides a favorable substrate for the growth of high-quality perovskite films. The PZ molecule also achieves effective regulation of perovskite crystallization kinetics through strong interaction with Pb2+ ions. These enhancements result in superior device performance, with the carbon-based PSCs (C-PSCs) without a hole transport layer achieving an efficiency of 20.29%, one of the highest efficiencies reported for C-PSCs. Meanwhile, the optimized device without encapsulation exhibits significantly improved continuous operation stability and air storage stability.