Improved performance of polymer solar cells by doping with Bi2O2S nanocrystals

Bismuth oxysulfide (Bi2O2S) has been demonstrated as a potential candidate for photovoltaic material because of favorite band gap (1.5 eV), effective charge dissociation, high carrier mobility, and long carrier lifetime. In this work, we synthesis the Bi2O2S nanocrystals by hydrothermal method, and incorporate Bi2O2S nanocrystals as a third component into poly[[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b'] dithiophene-2,6-diyl] [3-fluoro-2-(2-ethylhexy) carbonyl] thieno [3,4-b] thiophenediyl]] (PTB7):acceptor [6,6]-pheny C-71-butyric acid methy ester (PC71BM) binary polymer solar cells (PSCs). The results show that the power conversion efficiency (PCE) of ternary PSCs is obviously improved by 21.8% in comparison with binary PSCs (from 8.79% to 10.71%) by adding 1 wt% Bi2O2S nanocrystals. Introduction of Bi2O2S nanocrystals into the PTB7:PC71BM system can expand absorption range of sunlight in the PSCs, effectively enhance the crystallinity of PTB7 and optimize the surface morphology of photoactive layer, which leads to more efficient photon harvesting, enhances exciton dissociation, accelerates charge carrier transport and reduces charge recombination. Moreover, the addition of appropriate amounts of Bi2O2S nanocrystals into PTB7:PC71BM can effectively improve the lifetime of PSCs due to the improvement of crystallinity of PTB7. This work demonstrates the great potential use of bismuth compounds for photovoltaic devices fields.