Thiophene–Perylenediimide Bridged Dimeric Porphyrin Donors Based on the Donor–Acceptor–Donor Structure for Organic Photovoltaics

Two D–A–D (D = donor, A = acceptor)-based small-molecule donors, TPDI-2P and F-TPDI-2P, are designed and synthesized for organic solar cells (OSCs), with two strong donor porphyrin units bridged by either an electron-deficient diethynyl-substituted thiophene–perylenediimide (TPDI) linker for the former or a diethynyl-fused TPDI linker for the latter; 3-ethylrhodanine units were then flanked symmetrically by phenylenethynylene π-linkers. Both compounds show strong absorption profiles from 400 to 800 nm, with a valley at 600 nm, attributed to the Soret and Q-bands of porphyrin units. Compared to TPDI-2P, F-TPDI-2P with a fused TPDI backbone exhibits high redshifted absorptions and low-lying energy levels due to increased coplanarity of the dimeric porphyrin units. As a result, the optimized photovoltaic device based on F-TPDI-2P/PC₇₁BM has a decent power conversion efficiency (PCE) of 8.21%, whereas the device TPDI-2P/PC₇₁BM has a slightly lower PCE (6.90%). The higher efficiency of F-TPDI-2P/PC₇₁BM is mainly due to better photocurrent generation and smoother surface morphology with elevated charge carrier mobilities. The success of this molecular design strategy could be beneficial in the development of more efficient porphyrin-based donors for high-performance OSCs.