A small molecular acceptor based on dithienocyclopentaindenefluorene core for efficient fullerene-free polymer solar cells

Abstract

In recent years, acceptor–donor–acceptor (A–D–A) type of small molecules have become very promising non-fullerene acceptors (NFAs) to overcome the energy levels and absorption drawbacks of the fullerene-based acceptors in polymer solar cells (PSCs). A non-fullerene small-molecular acceptor named DTIF-IC with dithienocyclopentaindenefluorene (DTIF) as the electron-donating core sealed with 2-(3-oxo-indane-1-ylidene)-malononitrile as the electron-withdrawing groups was developed. The molecule exhibits strong absorption in the range from 550 to 720 nm and relatively high-lying lowest unoccupied molecular orbital (LUMO) energy level (−3.86 eV). Due to its up-shifted LUMO energy levels, high and balanced charge mobility and the homogeneous nanophase separations, the inverted polymer solar cells blending with the donor polymer poly[[2,6-4,8-di(5-ethylhexylthienyl)benzo[1,2-b;3,3-b]dithiophene]-[3-fluoro-2[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl]] (PTB7-Th) and DTIF-IC deliver a best power conversion efficiency (PCE) of 7.84% with relatively high open circuit voltage (Voc) of 0.95 V by thermal annealing treatment, which demonstrated that the DTIF-type small molecule could be the promising electron acceptor for high-performance polymer solar cells with a high Voc.