Enhancing Photon Utilization Efficiency for High‐Performance Organic Photovoltaic Cells via Regulating Phase‐Transition Kinetics

Abstract Efficient photon utilization is key to achieving high‐performance organic photovoltaic (OPV) cells. In this study, a multiscale fibril network morphology in a PBQx‐TCl:PBDB‐TF:eC9‐2Cl‐based system is constructed by regulating donor and acceptor phase‐transition kinetics. The distinctive phase‐transition process and crystal size are systematically investigated. PBQx‐TCl and eC9‐2Cl form fibril structures with diameters of ≈25 nm in ternary films. Additionally, fine fibrils assembled by PBDB‐TF are uniformly distributed over the fibril networks of PBQx‐TCl and eC9‐2Cl. The ideal multiscale fibril network morphology enables the ternary system to achieve superior charge transfer and transport processes compared to binary systems; these improvements promote enhanced photon utilization efficiency. Finally, a high power conversion efficiency of 19.51% in a single‐junction OPV cell is achieved. The external quantum efficiency of the optimized ternary cell exceeds 85% over a wide range of 500–800 nm. A tandem OPV cell is also fabricated to increase solar photon absorption. The tandem cell has an excellent PCE of more than 20%. This study provides guidance for constructing an ideal multiscale fibril network morphology and improving the photon utilization efficiency of OPV cells.