Enhancing the Comprehensive Performance of Carbon-Based Hole-Transport-Layer-Free CsPbI2Br Solar Cells via 5-Aminouracil Additive

Abstract

Carbon-based hole-transport-layer-free CsPbI₂Br solar cells are limited by high defect density and inefficient interfacial charge transfer. Herein, 5-aminouracil (5-AU) is introduced as a multifunctional additive to simultaneously regulate bulk defects and interfacial energetics. 5-AU forms Pb–O coordination and hydrogen bonding, effectively suppressing defect states and nonradiative recombination. Meanwhile, during the film fabrication process, a subset of 5-AU molecules can diffuse to the interface of the SnO₂/CsPbI₂Br, where they form molecular bridges that facilitate charge extraction and improve energy-level alignment. As a result, the 5-AU-modified device achieves a power conversion efficiency of 15.63% with an exceptional open-circuit voltage of 1.349 V, along with reduced hysteresis and significantly enhanced storage, thermal, and environmental stability.