Solid solution phenomenon in the amorphous conjugated polymer:fullerene bulk heterojunction structure.

Abstract The solid solution phenomenon in the amorphous PCDTBT:PC 71 BM blend was investigated. It has been disclosed that the PCDTBT:PC 71 BM blend with less than 20% PC 71 BM may form a kind of solid solution structure, which demonstrates a deeper HOMO level, a higher hole mobility, more free charges and less trap density than those of the pure PCDTBT film. It may well explain why the typical PCDTBT:PC 71 BM bulk heterojunction solar cells require higher PC 71 BM ratio to achieve a high power conversion efficiency. In that case, a portion of PC 71 BM is well intermixed with PCDTBT to form a solid solution phase and others form a pure PC 71 BM phase. It is the PCDTBT:PC 71 BM solid solution but not the pure PCDTBT to serve as the donor phases and to form interpenetrating networks with PC 71 BM phases. The PCDTBT:PC 71 BM solid solution phases favor to increase the V OC and enhance the charge collection leading to a high photovoltaic performance for the PCDTBT:PC 71 BM bulk heterojunction solar cells. Graphical abstract The PCDTBT:PC 71 BM blend with less than 20% PC 71 BM may form a kind of solid solution structure, which demonstrates a deeper HOMO level, a higher hole mobility, more free charges and less trap density than those of the pure PCDTBT film. A graphical schematic illustrates the interpenetrating networks composed of the solid solution and PC 71 BM in a practical PCDTBT:PC 71 BM BHJ solar cells. Image Highlights • The existence of the solid solution comprising of PCDTBT and PC 71 BM was confirmed by UPS and CV measurement. • Electric characteristics of the solid solution was studied by the FET and the varied temperature conductivity measurement. • The difference of photovoltaic characteristics between pure PCDTBT and the solid solution were compared. [ABSTRACT FROM AUTHOR]