Linked‐Acceptor Type Conjugated Polymer for High Performance Organic Photovoltaics with an Open‐Circuit Voltage Exceeding 1 V

A linked‐acceptor type conjugated polymer is designed and sythesized based on 4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene (BDTT) and linked‐thieno[3,4‐c]pyrrole‐4,6‐dione (LTPD). This polymer uses alkyl‐substituted thiophene as a bridge. The PBDTT‐LTPD includes two TPD units in one repeating unit, which can enhance acceptor density in the polymer backbone and lower the highest occupied molecular orbital (HOMO) level. By contrast, variable alkyl substitutions in the thiophene‐bridges ensure the subtle regulation of polymer properties. The solar cells based on PBDTT‐LTPD display an open‐circuit voltage (V_oc) that exceeds 1 V, and a maximum power conversion efficiency (PCE) of 7.59% is obtained. This PCE value is the highest for conventional single‐junction bulk heterojunction solar cells with V_oc values of up to 1 V. Given that PBDTT‐LTPD exhibits a low HOMO energy level and a band gap equivalent to that of poly(3‐hexylthiophene), PBDTT‐LTPD/phenyl‐C₆₁‐butyric acid methyl ester may be a promising candidate for the front cell in tandem polymer solar cells.