Alkyloxime-Substituted Thiophene-Based Wide-Band-Gap Polymer Donor Achieving a High Short Circuit Current Density of 30 mA cm^-2in Organic Solar Cells

A new polymer TTOTCl with a repeat unit consisting of a chlorinated thienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDTCl) donor unit, a thiophene spacer, and an alkyloxime-substituted thiophene (TO) acceptor unit is reported as a wide-band-gap donor for nonfullerene acceptor-based organic solar cells (OSCs). The optical band gap (E_g^opt= 1.97 eV), the highest occupied molecular orbital (HOMO) energy level (E_HOMO=-5.48 eV), and the lowest unoccupied molecular orbital (LUMO) energy level (E_LUMO=-3.51 eV) of TTOTCl match well with the nonfullerene acceptor Y6 (E_g^opt= 1.33 eV; E_HOMO=-5.65 eV; E_LUMO=-4.10 eV). TTOTCl also showed a high space charge-limited current (SCLC) hole mobility of 1.36 × 10^-3cm²V^-1s^-1. OSCs using TTOTCl as the donor and Y6 as the acceptor achieved a high power conversion efficiency (PCE) of up to 14.42% with a record high J_scof 30.00 mA cm^-2along with a V_ocof 0.70 V and a fill factor (FF) of 0.68. The PCE was further improved to 15.43% using a hole transport enhancement layer, with an enhanced V_ocand FF of 0.72 V and 0.71, respectively. The unencapsulated OSC device showed excellent long-term stability in ambient air with a 90.4% retention in the PCE over 30 days.