Researchers from Shenzhen University and Ocean University of China have reported the development of a small-molecule cathode interfacial material, HL220, aimed at improving the performance and stability of inverted perovskite solar cells (PSCs). The team addressed interfacial energy-level mismatch, defect formation, and electrode degradation - factors that currently limit device efficiency in inverted (p–i–n) architectures.
HL220 features a donor–acceptor–donor–acceptor–donor (D–A–D–A–D) fused-ring molecular framework that provides strong conjugation and high planarity. These structural attributes facilitate efficient electron delocalization, as evidenced by dual absorption peaks at approximately 544 nm and 580 nm. The molecule can be processed from alcohol-based solutions and forms cohesive, smooth films when deposited on PCBM, indicating good solution compatibility and film uniformity. After HL220 modification, the PCBM surface exhibited reduced roughness and improved wettability, pointing to enhanced interfacial contact.
The team noted that HL220 can chemically interact with silver electrodes, leading to a reduction in the metal’s work function. This adjustment decreases the electron-extraction barrier at the PCBM/Ag interface and improves charge transfer characteristics. Combined electrical and morphological analyses suggest that HL220 effectively suppresses interfacial recombination and reduces series resistance across the device.
The optimized inverted PSC incorporating HL220 achieved a power conversion efficiency (PCE) of 26.44% and a fill factor (FF) of 85.2%. For a large-area (15 cm²) module, a PCE of 22.93% was obtained, demonstrating good scalability. Stability measurements indicated that the unencapsulated devices retained 94.1% of their initial efficiency after continuous illumination for 450 hours, attributed to improved interfacial and electrode stability.
Overall, HL220 functions as an effective cathode interfacial layer that simultaneously improves film morphology, energy-level alignment, and electrode contact. The results highlight the potential of small-molecule interlayers for achieving high-efficiency, durable inverted perovskite solar cells suitable for further scale-up and practical application.
