Fabrication of Organic Solar Cells with Branched Cauliflower-Like Nano Structures as a Back Electrode Replicated from a Natural Template of Cicada Wing Patterns

Nanostructures of noble metal materials have been used in organic solar cells for enhancement of performance and light trapping. In this study, we have introduced branched silver cauliflower-like nanopatterns as sub-wavelength structured metal grating in organic solar cells. Self-assembled fabrication process of branched nanopatterns was carried out on a bio-template of cicada wing nanonipple arrays using a gas aggregation dc magnetron sputtering nanocluster source without size filtration. The branched nanostructures provide surface gaps with dimensions near the organic exciton diffusion length, which prevents recombination of charge carriers. An increased power conversion efficiency of 14.8% compared to that of the planar device was achieved mainly due to the enhancement in the short-circuit current density. Besides, these branched cauliflower-like nanopatterns had enhanced optical light absorption in the solar cell as a result of enhancing the optical path length of the reflected light in the active layer and plasmonic effects of the noble metal material.