Efficient all-small-molecule organic solar cells based on a fluorinated small-molecule donor

Abstract

In this paper, a new small-molecule donor with a fluorinated benzodithiophene core and rhodanine analogue end groups, named BTEHR-FT, has been designed and synthesized, which has excellent solubility and thermal stability for solution-processed device fabrication. Moreover, BTEHR-FT shows a low-lying highest occupied molecular orbital (HOMO) energy level of −5.45 eV due to the introduction of fluorine atoms. When blended with a nonfullerene acceptor F-2Cl, the BTEHR-FT based all-small-molecule organic solar cell (ASM-OSC) exhibits a high open-circuit voltage (V_oc) of 0.948 V as expected, but a low short-circuit current density (J_sc) of 12.10 mA cm⁻² and fill factor (FF) of 0.658 due to the bad morphology of the active layer, giving a moderate power conversion efficiency (PCE) of 7.55%. After thermal annealing treatment, a promising PCE of 10.71% was obtained benefiting from the great enhancement of J_sc (16.59 mA cm⁻²) and FF (0.693), which is among the highest values for non-Y series acceptor-based ASM-OSCs reported to date. This work provides a guideline for the design of small-molecule donors for efficient organic solar cells.