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

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.