Exploiting optical anisotropy to increase the external quantum efficiency of flexible P3HT:PCBM blend solar cells at large incident angles

The external quantum efficiencies of P3HT:PCBM blend solar cells decrease significantly when they are bent or illuminated at large incident angles because of (i) optical anisotropy of the P3HT:PCBM films—primarily because a mismatch between the direction of the electric field of the incoming light and the orientation of the P3HT:PCBM blend nanocrystallites results in a significant reduction in the amount of TM-polarized light absorbed and (ii) interfacial reflection of multilayer structures - primarily because the outermost air-flexible substrate interface exhibits a distinct refractive index difference - at large incident angles. Textured moth-eye structures fabricated by nanoimprint lithography on the flexible substrates of organic solar cells reduce the degree of interfacial reflection at high incident angles; they should allow more TE-polarized light to absorb in the P3HT:PCBM films (active layers) of the organic solar cells.