Bis-EH-PFDTBT:PCBM solar cells: A compositional, thickness, and light-dependent study

Poly{[2,7-(9,9-bis-(2-ethylhexyl)-fluorene)]-alt-[5,5-(4,7-di-2'-thienyl-2,1,3-benzothiadiazole)]}: PCBM bulk heterojunction solar cells were fabricated and characterized under different incident light power intensities. Charge-trapping effects take place at low fullerene content in the photoactive blend; an efficient polymer fullerene intermixing with formation of continuous phases is reached at a donor: acceptor ratio of 1:4. For an optimized active layer thickness of 100 nm, a power-conversion efficiency of 2.57% was obtained. Photocurrent measurements under reverse-bias conditions show that a high percentage of the photogenerated excitons does not lead to the formation of free carriers, thus representing the major limiting factor for the device's efficiency. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3665126]