Precisely control the morphology and crystallization of temperature-dependent aggregation bulk heterojunction by using co-solvent system for optimized light intensity distribution and its effect on thick active layer polymer solar cells

The effects of co-solvent on the morphology, crystallization and light intensity distribution of thick bulk heterojunction (BHJ) polymer solar cells (PSCs) based on polymer of [(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3000-di(2-octyldodecyl)-2,20,50,200,500,2000-quaterthiophen-5,5000-diyl)](PffBT4T-2OD):[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) are studied. By adjusting different co-solvent systems in thick BHJ layer, it is found that the polymer crystallization, fullerene absorption and PffBT4T-2OD:PC71BM BHJ morphology are optimized by using a co-solvent of chlorobenzene (CB):dichlorobenzene (DCB):1,8-diiodooctanein (DIO). The optimized BHJ thickness of 250 nm is analyzed by using transfer matrix theory, resulting in enhanced FF and PCE of 66.7% and 9.16%, respectively. This phenomenon is due to the active layer can absorb 90% of the incident light with a thickness of 250 nm, which contributes to the light intensity distribution and exciton generation rate.