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.

The combination of optical anisotropy of P3HT:PCBM blend films and interfacial reflection results in a loss of external efficiency for organic solar cells that are bent or illuminated at large incident angles. Experimental results and simulations confirmed that the presence of the textured structures led to obvious reductions in the degrees of external efficiency loss from bent solar cells.Figure optionsDownload as PowerPoint slideHighlights
► We investigate the external quantum efficiency loss of bent organic solar cells throughout.
► The optical anisotropy phenomenon of active layer is fully discussed.
► We display that optical anisotropy leads to obvious anisotropic absorption under TM-polarized light.
► We investigate the interfacial reflections that reduce the absorption under TE-polarized light.
► Nanoimprint lithography is used to fabricate moth-eye structure to reduce the efficiency loss of a bent device.