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

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 (VOC) 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 π-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 π–π 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 π-bridge and fluorine substituents are effective to finetune the optoelectronic properties of p-type polymers to realize high VOC and PCE, which can expand the choice of material combination for SAS.