Novel Ternary Blend of PCDTBT, PCPDTBT and PC70BM for the Fabrication of Bulk Heterojunction Organic Solar Cells

Abstract Bulk heterojunction organic solar cells with interface compatibility of donor and acceptor materials are promising candidates for the fabrication of solar cells because of solution processability, mass production, and environment friendliness. To improve the absorption range of binary blend devices, ternary blends with two push pull polymer donor materials and one fullerene acceptor material is developed. Push-pull polymers are a class of organic polymers with alternating electron deficient and electron rich units for easy transfer of charge carriers. In this paper, we discuss a ternary blend of two push-pull donor materials PCPDTBT (Poly[2,1,3-benzothiadiazole-4,7-diyl[4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b']dithiophene-2,6-diyl]]), PCDTBT ([Poly [N-9'- heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]) and one acceptor material PC 70 BM([6,6]-Phenyl-C71-butyric acid methyl ester). It is found that the combination of these two donor materials gave better results in terms of efficiency and consistency than individual donor materials. The reason for this increase is the extension of absorption spectrum from the visible to the infrared region due to the addition of PCDTBT and PCPDTBT to the acceptor material. Also, there is cascading of energy levels between the highest occupied molecular orbital and the lowest unoccupied molecular orbital from the dominating donor material to the acceptor material to facilitate charge transport. Morphology studies such as Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) showed that the ternary blend exhibited better nano-morphology than the binary blend which is the primary reason for the improvement in efficiency.