Enhanced performance of bulk heterojunction solar cells using double layers deposition of polymer:fullerene derivatives

Abstract

Poly[4,8-bis(2-ethylhexyloxy)benzo[1,2-b:4,5-b′]dithiophene-co-quinoxaline] (PBDTQx) copolymer; to be used as an electron donor in bulk heterojunction (BHJ) polymer solar cell; was synthesized from benzo[1,2-b:4,5-b′]dithiophene and quinoxaline via a Stille coupling reaction. BHJ polymer solar cells based on the ternary blend of PBDTQx; indene-C60 bisadduct (ICBA) and [6,6]-phenyl-C71-butyric-acid-methyl-ester(PC71BM) were then fabricated and tested for the power conversion efficiency (PCE) values. From the IV curves; it was found that the open circuit voltage (Voc) and current density (Jsc) of the solar cell increased with the addition of ICBA. This was related to the lowest unoccupied molecular orbital (LUMO) level of ICBA; which is suitable with those of PC71BM and PBDTQx. It was also found that PCE of the solar cell can be improved significantly by double layers coating of the active materials (PBDTQx:PC71BM:ICBA). The above effect was ascribed to changes in morphology and crystallinity of the active layer.