Ring fusion attenuates the device performance: star-shaped long helical perylene diimide based non-fullerene acceptors

The past six years have witnessed tremendous progress in the area of perylene diimide (PDI) based non-fullerene organic solar cells (OSCs). In order to obtain high performance OSCs, ring fusion has been proposed as an efficient approach to achieve a trade-off between suppressing the self-aggregation and maintaining the charge-transfer properties of 3D-shaped PDI derivatives. By using two star-shaped PDI-based small molecule acceptors (SMAs), TPDI3 and FTPDI3, we demonstrated here the violation of this molecular design concept for the first time. OSCs were fabricated by using these two compounds as electron acceptors and the commercially available PTB7-Th as the electron donor. The non-fused TPDI3 based devices exhibit a power conversion efficiency (PCE) of 8.84%, which is higher than that of the fused counterpart FTPDI3 (7.93%). This illustrates that ring-fusion is detrimental to the device performance in the case of TPDI3 and FTPDI3. This result provides new insight into the design of novel PDI based non-fullerene acceptors for high performance OSCs.