Self-passivated coal-derived carbon nanotubes enable defect-engineered interfaces for high-performance carbon-based perovskite solar cells

The strategic design of hole transport layers (HTLs) with dual functionality in interfacial charge regulation and recombination suppression represents a critical pathway for advancing carbon-based perovskite solar cells (Carbon-PSCs). This study presents a facile synthesis of coal-derived carbon nanotubes (C-CNTs) characterized by self-passivated surfaces enriched with oxygen-containing moieties (-COOH, -OH). This unique structural architecture imparts dual functional superiority through intrinsic aqueous dispersibility that eliminates the need for post-synthesis processing, as well as self-regulated charge redistribution driven by the electron-withdrawing nature of the -I effect. These features work in synergy to establish anisotropic hole transport networks that enforce electronic confinement. When integrated as HTLs in Carbon-PSCs, the oxygen-functionalized C-CNTs significantly reduce interfacial recombination losses, achieving a champion power conversion efficiency (PCE) of 14.25% with only 10 wt% C-CNTs. The modified device structure, FTO/SnO 2 /CH 3 NH 3 PbI 3 /C-CNTs/Carbon, demonstrates performance surpasses that of the pristine device (structure: FTO/SnO 2 /CH 3 NH 3 PbI 3 /Carbon, PCE: 11.99%) by 18.85%, and approaches the performance of the device with commercial high-purity CNTs (>95 wt%, structure: FTO/SnO 2 /CH 3 NH 3 PbI 3 /Commercial-CNTs/Carbon, PCE: 14.44%). By repurposing coal as a sustainable precursor for optoelectronic materials, this work pioneers a defect-mediated interfacial engineering paradigm for solution-processed photovoltaic systems.