Efficiency enhancement for bulk heterojunction photovoltaic cells via incorporation of alcohol soluble conjugated polymer interlayer

Three dimensional conjugated polymers with pendant ionic ammoniums or polar amines and their linear analogues as cathode interfacial layers were used for organic photovoltaic cells based on blends of poly [(9,9-di-n-octyl-2,7-fluorene)-alt-(5,5-(4',7'-di-2-thienyl)-2',1',3'-benzothiadiazole)] (PFOTBT) or poly(3-hexylthiophene) as the donor and [6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM) as the acceptor. The alcohol soluble conjugated polymer interlayers can improve the device performance significantly by simultaneous enhancements of the open-circuit voltage, short-circuit current density, and fill factor. An increase of the power conversion efficiency from 2.62% to 4.67% by 78% was observed with poly[(2,7,2',7'-spirobifluorene-co-(9,9-bis (6'-((N,N,N-trimethyl)ammonium)hexyl)-2,7-fluorene) dibromide)] based on PFOTBT-PC61BM blend. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4719522]