Constructing a donor-acceptor linear-conjugation structure for heterologous perylene diimides to greatly improve the photovoltaic performance

By applying the concept of an acceptor-donor-acceptor (A-D-A) structure, we have designed a new linear-conjugation perylene diimide (PDI) derivative Th-4PDI that contains four PDI units connected at different reactive positions. Th-4PDI is constructed via a coupling reaction between two heterologous PDI dimers (2PDI) as the acceptor parts and a thiophene as the donor unit. Th-4PDI possesses a broadened absorption spectrum in the region of 400 to 700 nm and a deep lowest unoccupied molecular orbital (LUMO) level of -4.03 eV. More importantly, the active layer films based on Th-4PDI exhibit a higher charge mobility, more balanced carrier transport and more favorable nanomorphology than those of the prototype 2PDI, which are important factors for achieving high efficiency in organic solar cells (OSCs). As a result, the device based on PTB7-Th: Th-4PDI shows a high power conversion efficiency (PCE) of 7.17%, which is 3 times higher than that of 2PDI. The results demonstrate that constructing A-D-A type conjugated structures based on 2PDI is a feasible strategy to achieve high PCEs in OSCs and also, with a rational design, the heterologous PDI arrays could be developed into high efficiency non-fullerene electron acceptor materials.