A Rational Design and Synthesis of Cross-Conjugated Small Molecule Acceptors Approaching High-Performance Fullerene-Free Polymer Solar Cells

Considering the combination of the advantages of both the acceptor-donor-acceptor and perylene diimide type acceptors, three new cross-conjugated small molecule non-fullerene acceptors were rationally designed and synthesized. Their thermal, optical, electrochemical, and photovoltaic properties were systematically investigated. These acceptors exhibit highly extended absorption spectra ranging from 300 to 700 nm as well as appropriate lowest unoccupied molecular orbital levels compared with those of the general acceptors based on perylene diimide. Non-fullerene polymer solar cells based on the resultant acceptors were fabricated in the ITO/PEDOT:PSS/PTB7-Th:acceptor/PFN-Br/Ag configuration. Benefiting from efficient exciton dissociation, reduced bimolecular recombination, and enhanced and balanced electron mobility, the device-based PDIBDT-IT exhibited a power conversion efficiency (PCE) of 6.06% with a high short-circuit current density (J(SC)) of 13.60 mA/cm(2), a fill factor (FF) of 60.45%, and an open-circuit voltage (V-OC) of 0.74 V, which was higher than those of PDIBDT-RDN and PDIBDT-ITF. The underlying mechanism was carefully studied and discussed. The extended absorption of PDIBDT-IT contributes to its relatively high PCE; however, the performance will be potentially improved by ehnancing the electron mobility of these acceptors. Our results provide an efficient cross-conjugated approach and great flexibility in fine-tuning physicochemical properties, including absorption spectra and energy levels of the acceptors toward high-performance solar cells.