Optimizing binding energy and electron-hole pair binding distance for efficient organic solar cells with low voltage loss

Abstract

The energy loss during exciton dissociation is one of key reasons for organic solar cells (OSCs) with inferior performance. Herein, a theoretical and experimental guidance for highly efficient OSCs with outstanding exciton dissociation rate is introduced via fine-tuning the binding energy (Eb) and the electron-hole pair binding distance (a) in the charge transfer (CT) state. Results suggest that decreasing the Eb appropriately is favorable for higher photovoltaic conversion efficiency (PCE). Hence, we attempt to modulate the Eb of PM6:Y6 photoactive layer by changing additive and their corresponding concentration. Investigations show that the Eb of PM6:Y6 changes slightly with different additives, and the chloronaphthalene (CN) with appropriate concentration affords an Eb of 0.14 eV, and thus supporting the excellent efficiency of 16.14%. Meanwhile, the influences of the internal spacing of electron and hole in CT state on device performance were explored for further elucidating carrier micro-transport mechanism and instructing further experimental investigation.