Perovskite Coupled NIR Organic Hybrid Solar Cells Achieving an 84.2% Fill Factor and a 25.2% Efficiency: A Comprehensive Mechanistic Exploration

The integration of organic dyes in perovskite solar cells (PSCs) to utilize near-infrared (NIR) photons remains a challenge. In this study, a selenium-incorporated ortho-benzodipyrrole-based NIR dye CB-2Se was developed. CB-2Se, featuring a lower bandgap of 1.35 eV, was blended with PCBM to form a bulk-heterojunction layer in PSCs for electron extraction and transport. Compared to Y6-16 acceptor, the removal of the Tz unit in CB-2Se suppresses self-aggregation, improving its compatibility with PCBM. A CB-2Se:PCBM-incorporated PSC achieved a remarkable power conversion efficiency (PCE) of 25.18% with a VOC of 1.164 V, a JSC of 25.71 mA/cm², a Fill Factor of 84.15%, outperforming that of the PCBM-only reference device (24.35%) and the PCBM:Y6-16-based device (24.49%). The PCBM:CB-2Se layer enhanced the long-term stability of PSCs, retaining 88% of its initial efficiency after 1000 h under ambient air and thermal conditions. The photophysical interactions between NIR dyes and PSCs have been comprehensively investigated by using femtosecond transient absorption spectroscopy. Ultrafast exciton separation into free charges occurs within 200 femtoseconds at the interfaces between PCBM and CB-2Se. For the first time, a transfer of holes from CB-2Se back to the perovskite was detected, providing valuable insights into the charge dynamics of PSCs utilizing NIR dyes.