Enhancing the J_SC of P3HT-Based OSCs via a Thiophene-Fused Aromatic Heterocycle as a "π-Bridge" for A-π-D-π-A-Type Acceptors

Poly(3-hexylthiophene) (P3HT)-based organic solar cells (OSCs) have been extensively studied due to unique advantages of P3HT such as roll-to-roll and large-area printing fabrication, but a poor short-circuit current density greatly limits the enhancement of power conversion efficiency (PCE). Herein, via the thiophene-fused aromatic heterocycle as a "π-bridge", two "A-π-D-π-A"-type acceptors have been designed and synthesized for P3HT-based OSCs. The aromaticity of the fused thiophene ring has effectively stabilized the quinoid population, thus strengthening the intramolecular charge transfer and further improving the current density. Owing to the weaker electron-withdrawing ability of the thiophene-fused benzotriazole unit in JC2 than the thiophene-fused benzothiadiazole unit in JC1, a blue-shifted absorption occurs for JC2 to show a better complementarity with P3HT to improve the light-harvesting efficiency and current density of the derived OSCs, and an uplifted lowest unoccupied molecular orbital energy level is also achieved for JC2 to obtain higher voltages. Thus, the P3HT:JC2-based device exhibits a PCE of 6.24% with a high J_SC of 13.96 mA cm^-2 and a V_OC of 0.71 V, significantly exceeding those of the P3HT:JC1 device with a PCE of 2.80%, a J_SC of 10.66 mA cm^-2, and a V_OC of 0.48 V. This indicates that the fusion of a thiophene ring onto a benzotriazole unit is an effective strategy to balance the V_OC and J_SC of P3HT-based OSCs to achieve excellent photovoltaic performances.