Enhancing the Comprehensive Performance of Carbon‐Based Hole‐Transport‐Layer‐Free CsPbI ₂ Br Solar Cells via 5‐Aminouracil Additive

Carbon‐based hole‐transport‐layer‐free CsPbI 2 Br 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 SnO 2 /CsPbI 2 Br, 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.