Bi@MIL-101(Fe) dual-functional hole transport layer for stable and efficient carbon-based perovskite solar cells via synergistic defect-energy modulation

Hole transport layer (HTL) is crucial for enhancing the efficiency and stability of carbon-based perovskite solar cells (C-PSCs). However, conventional organic HTL suffer from intrinsic limitations, including interfacial corrosion, energy-level mismatch, and poor environmental resilience, which critically hinder device performance. In this study, we propose a novel inorganic HTL, bismuth-doped Fe-based metal-organic framework (Bi@MIL-101(Fe)), to address these challenges through rational interface engineering. The Bi@MIL-101(Fe) HTL synergistically coordinates electron-rich carbonyl (-C=O) groups with undercoordinated Pb2+ at the perovskite surface, effectively passivating defects and suppressing non-radiative recombination. Furthermore, the incorporation of Bi optimizes energy band alignment, facilitating efficient hole extraction and transport. The optimized C-PSC device achieves a remarkable power conversion efficiency (PCE) of 16.00 % (compared to 11.90 % for the pristine device), with enhanced fill factor (FF, 68.16 %) and short-circuit current density (JSC, 24.13 mA cm−2). Crucially, the Bi@MIL-101(Fe)-integrated device demonstrates exceptional environmental stability, retaining 85.67 % of its initial PCE after 1080 h of exposure to ambient conditions (T: 20–30 °C, RH: 25–55 %) without encapsulation. This work underscores the dual functionality of Bi@MIL-101(Fe) as both a defect-passivating agent and an energy-level mediator, providing a strategic pathway for developing robust inorganic HTL in next-generation photovoltaics.