Structural regulation of thiophene-fused benzotriazole as a "π-bridge" for A-π-D-π-A type acceptor:P3HT-based OSCs to achieve high efficiency

Poly(3-hexylthiophene) (P3HT) is regarded as one of the most promising polymer donors for organic solar cells (OSCs) owing to its own merits of low-cost and controllable synthesis, and large-area and roll-to-roll printing device fabrication. However, the mutual restriction and imbalance of the open-circuit voltage (V-OC) and short-circuit current density (J(SC)) greatly limits further breakthrough of power conversion efficiency (PCE) for P3HT-based OSCs. Herein, a new A-pi-D-pi-A type acceptor (JC14) with the same conjugated skeleton as that of our previous acceptor (JC2) has been designed through removing an electron-withdrawing ester group from a thiophene-fused benzotriazole (BTAZT) unit as a "pi-bridge". In comparison, JC14 retains the BTAZT unit that can still stabilize the quinoid structure of the conjugated backbone to favor J(SC). Remarkably, the fine structural regulation of the "pi-bridge" significantly raises the LUMO energy level of JC14, which is more conducive to the enhancement of V-OC. Thus, the P3HT:JC14-based OSC device achieves very balanced and high J(SC) (J(SC) = 16.04 mA cm(-2)) and V-OC (V-OC = 0.759 V) that leads to a high PCE of 7.72%, while the P3HT:JC2-based device shows a relatively lower PCE of 6.12% with J(SC) of 14.53 mA cm(-2) and V-OC of 0.685 V.