Photovoltaic studies on perylene diimide-based copolymers containing electronic push-pull chromophores

Soluble perylene diimide-based copolymers with conjugated electronic push-pull substituent species (piperidinyl and 4-tert-butylphenoxyl) on the 1,7-bay position of the perylene core and a 5,5'-bis(4-aminophenyl)-2-2'-bifuryl as terminal group were synthesized and characterized in order to fabricate bulk heterojunction solar cells. The introduction of such electronic push-pull substituents, which results in relatively low-lying HOMO and high-lying LUMO energy levels, was achieved experimentally using absorption and cyclic voltammetric measurements and also by density functional theory. Successfully fine-tuned HOMO and LUMO energy levels translated into a high open circuit voltage (V-oc > 1.0 V) in fabricated photovoltaic devices of type ITO/PEDOT:PSS/rr-P3HT:Perylene diimide-based copolymers/Ca/Al. However, a relatively poor fill factor and efficiency may be observed due to the large degree of aggregation domains, which are observed from atomic force microscopic studies.