Near-infrared non-fused ring acceptors with light absorption up to 1000 nm for efficient and low-energy loss organic solar cells

It is challenging to afford both high-performance and low-energy loss ( E loss ) organic solar cells (OSCs) based on near-infrared (NIR) non-fused ring electron acceptors (NFREAs) with ultra-narrow bandgap. Herein, three simple NFREAs ( C6OT-4F , C6EDOT-4F and PDOT-4F) with absorption up to 1000 nm are developed by using alkoxy substituted thiophene derivatives core connected to fluorinated 1,1-dicyanomethylene-3-indanone (DFIC) terminals through 4H-cyclopenta[1,2-b:5,4-b’]dithiophene (CPDT) bridge. It is found that fine tuning central thiophene derivatives can surprisingly lead to different photoelectric properties and the device performances. Compared with C6EDOT-4F and PDOT-4F , C6OT-4F shows a blue-shifted absorption and an elevated LUMO level, which is beneficial for boosting V oc . As a result, optimal devices based on PTB7-Th: C6OT-4F achieve a preferable efficiency of 9.83% with a low E loss of 0.47 eV, which is the lowest E loss among the NFREA-based OSCs with PCE >9% and optoelectronic response over 1000 nm. This work portrays the design concept of ultra-narrow bandgap NFREAs for efficient OSCs as well as low energy loss and exploration of semitransparent photoelectric devices. • Three ultra-narrow bandgap NFREAs with light absorption up to 1000 nm were synthesized. • The best PCE of 9.83% with a remarkably low E loss of 0.47 eV was achieved by using simple processing method without additive. • The high efficiency is associated with the low charge recombination and favorable miscibility between donor and NFREA. • Semitransparent organic solar cells were prepared and achieved a PCE of 4.54% and average visible transmittance of 19.2%.