Novel A-π-D-π-A-type BODIPY dyads as small-molecule donors for solution-processed organic solar cells

Abstract

The boron dipyrromethane (BODIPY) unit has attracted interest due to its strong molar extinction coefficient and tunable electrochemical properties, and thus, currently, BODIPY-based organic photovoltaic materials featuring near-infrared absorption and deep HOMO levels are widely constructed and investigated. Herein, two novel A-π-D-π-A-type BODIPY small-molecule donors (SMDs), namely, CTBDP and DCTBDP, in which carbazole and indolo-[3,2-b]carbazole as the electron-donating core (D) connect the electron-withdrawing BODIPY moiety (A) with thiophene as a π-bridge, respectively, were designed and synthesized via Stille coupling reaction with a “D-π” segment at the β-site of BODIPY. CTBDP and DCTBDP exhibited a deep-lying HOMO level of −5.46 eV and −5.34 eV and narrow optical bandgap of 1.51 eV and 1.56 eV, respectively, together with a broad absorption in the range of 300–900 nm in films. Interestingly, the CTBDP-device exhibited an impressive PCE of 5.85% with an outstanding J_sc of 17.70 mA cm⁻² and V_oc of 0.81 V, which are the highest PCE and J_sc values reported to date for A–D–A-type BODIPY-SMDs for solution-processed OSCs. Our work demonstrates that carbazole/indolo[3,2-b]carbazole-BODIPY conjugated small molecules can simultaneously achieve a narrow bandgap and low HOMO level via their rational molecular design, which provides crucial guidance for the development of high-efficiency BODIPY-based photovoltaic materials in the future.