Organic solar cells featuring nanobowl structures

Although organic solar cells having a bilayer configuration provide continuous conducting pathways for carrier transport to the requisite electrodes, their efficiencies have remained low because of the short exciton diffusion lengths of organic semiconductors. In this paper, we describe unique spatial organic solar cells featuring nanobowl array structures that capture more light and generate more power than planar organic solar cells. To construct bilayer solar cells, we used electrochemical deposition (with polystyrene beads as the template) to fabricate poly(3,4-ethylenedioxythiophene) nanobowl arrays, functioning as the hole extraction layer, on indium tin oxide substrates and then deposited copper phthalocyanine and a fullerene (C-60 or C-70) to function as the active layer, onto the nanobowl arrays. By implementing this spatial structure, we could control the active layer's thickness, such that it would be suitable for exciton dissociation, while maintaining a high absorption of incident light (by increasing the absorber volume without decreasing the area of the donor-acceptor interface, such that the light path in the active layer was increased) and ensuring high exciton dissociation efficiency (by enlarging the donor-acceptor interface). Relative to an equally thick planar control active layer the photocurrent generated by such bilayer solar cells increased by approximately 90%.