Hyperbranched conjugated polymers based on 4,7-di(thiophen-2-yl)benzo [c] [1,2,5]thiadiazole for ternary organic solar cells

A new class of end-modifiable hyperbranched conjugated polymer (HBCP-Br) was synthesized from an AB(2) monomer, and the end-modification of HBCP-Br was carried out by substituting the end-Br with a donor group to give the end-modified HBCPs (HBCP-OR). Both polymers had relatively good thermal stability (T-d > 350 degrees C) and deep HOMO energy levels (-5.40 eV for HBCP-OR, -5.45 eV for HBCP-Br). Besides, the other two similar small molecular acceptors (IDTOTZ and IDTCPT) were synthesized to construct ternary organic solar cells (OSCs) with HBCP-OR or HBCP-Br. Owing to the favorable spectral and energy levels matching and relatively regular morphology, the ternary OSCs based on HBCP-OR/IDTOTZ/IDTCPT obtained an optimized PCE of 4.86% (with an open-circuit voltage (V-OC) of 0.893 V, a short-circuit current density (J(SC)) of 11.71 mA, and a fill factor (FF) of 45.18%), which performed better than the devices based on HBCP-Br/IDTOTZ/IDTCPT with a PCE of 2.33%. In addition, the HBCP-Br also exhibited photovoltaic activity when used as acceptors in the ternary OSCs based on small molecular donors, which demonstrated that HBCPs could play different roles in the OSCs.