Indacenodithiophene Bridged Dimeric Porphyrin Donor and Absorption Complementary Indacenodithiophene Acceptor for Nonfullerene Organic Photovoltaics

Porphyrins are one of the most promising materials for organic photovoltaics (OPVs) because of their easily tunable functional groups. Herein, we present the design and synthesis of two porphyrin-based small molecule donors, IDT-2TPE and TPE, in which two porphyrin units are bridged by an indacenodithiophene (IDT) diethynylene unit for the former and a single porphyrin monomer for the latter, and 3-ethylrhodanine units are then end-capped symmetrically by phenylenethynylene π-linkers. The porphyrin dimer IDT-2TPE exhibits outstanding red-shifted absorptions with a valley in both solution (400-800 nm) and film (400-900 nm), low-lying energy levels, and excellent thermal stability compared to the porphyrin monomer TPE due to the extended π-conjugation and increased rigidity with the IDT unit. Impressively, the device based on the IDT-2TPE donor and IDTCR nonfullerene acceptor shows a broad photoelectron response up to 1000 nm and a power conversion efficiency (PCE) of 10.41% at AM 1.5G. For comparison, the device based on the TPE donor and IDTCR acceptor has a much lower PCE of 4.22%. The much better performance of the device IDT-2TPE/IDTCR is attributed to its higher photocurrent generation and more favorable surface morphology with elevated charge carrier mobilities.