Benzotriazole-Based p-Type Polymers with Thieno[3,2-b]thiophene π-Bridges and Fluorine Substituents To Realize High VOC

On the basis of the success of the Same-Acceptor-Strategy (SAS) in constructing p-type and n-type photovoltaic material combination to realize high open-circuit voltage (V-OC) beyond 1.1 V, we designed and synthesized two new benzotriazole (BTA)-based conjugated p-type polymers. PE1 was derived from the classical polymer J61 by replacing the thiophene pi-bridge with thieno[3,2-b]thiophene (TT) due to its rigid structure and the linear polymer backbone conformation, which are benificial for enhancing the effective conjugation length and intermolecular pi-pi stacking. By further introducing fluorine atoms to the thiophene side chain in PE1, the final polymer PE2 can thus realize a downshifted highest occupied molecular orbital energy level of -5.41 eV. Utilizing SAS and adopting a benzotriazole-containing small molecule BTA3 as electron acceptor, PE1 can realize a slightly improved power conversion efficiency (PCE) of 8.43% than that of J61 (8.25%) with a Voc of 1.11 V. Furthermore, PE2:BTA3 combination can attain a extremely high Voc of 1.26 V with a moderate PCE of 5.83%, which is one of the best results for organic solar cells with Voc beyond 1.2 V. Our results indicate that the incorporation of TT pi-bridge and fluorine substituents are effective to finetune the optoelectronic properties of p-type polymers to realize high V-OC and PCE, which can expand the choice of material combination for SAS.