Nickel Chlorophyll-Derived Hole Transport Materials for Stable and Efficient Inverted Perovskite Solar Cells

Hole-selective layers (HSLs) are critical for efficient and stable perovskite solar cells (PSCs). Chlorophylls (Chls) and their analogs exhibit unique optoelectronic properties, making them attractive for photovoltaics. However, dopant-free Chl-based materials remain underexplored, with reported power conversion efficiencies (PCEs) below 19%. This study investigates three nickel chlorins (NiChls) as monomers for functional materials. Nickel methyl pyropheophorbide-a (NiChl-Oxo), derived from natural Chl-a, was chemically modified at the C13-keto-carbonyl group, yielding NiChl-Deoxo and NiChl-CN. Electrochemical polymerization was used to fabricate the corresponding polymerized NiChl films as HSLs. Without dopants, NiChl-Deoxo-based PSCs achieved a record PCE of 21.8%, with a fill factor of 83.8%, which is the highest reported efficiency for Chl-based PSCs to date. Additionally, these devices exhibited exceptional long-term stability. This study highlights the effectiveness of strategic molecular modifications in advancing Chl-based materials and presents a promising pathway for developing high-performance, dopant-free HSLs for next-generation PSCs.