Thiophene–Perylenediimide\nBridged Dimeric Porphyrin\nDonors Based on the Donor–Acceptor–Donor Structure for\nOrganic Photovoltaics

Abstract

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