Rational design of coralloid Co9S8–CuS hierarchical architectures for quantum dot-sensitized solar cells

Abstract

Metal sulfide nanostructures, which have been widely studied in recent years, are one of the most promising candidates in energy devices. Herein, coralloid hierarchical structures composed of Co₉S₈ hollow nanoneedle trunks and CuS nanosheet branches are, for the first time, well-constructed on fluorinated tin oxide (FTO) substrates via a multistep route. A seeding assistant strategy is applied to grow uniform and firm metal sulfide films on the FTO substrates. It is revealed that different seeds (i.e., TiO₂, CuS and ZnO) all have a positive effect to facilitate the film growth because of their surface roughening behavior on the FTO substrates. Significantly, such three dimensional (3D) Co₉S₈–CuS electrodes show superior electrocatalytic performance in the reduction reaction of polysulfide electrolyte, and yield an enhanced power conversion efficiency of 4.50% for CdS/CdSe quantum-dot sensitized solar cells as counter electrodes when compared with the one dimensional (1D) Co₉S₈ hollow nanoneedle (3.25%) and two dimensional (2D) CuS nanosheet (3.83%) electrodes. More impressively, the coralloid structure exhibits excellent stability in the electrochemical cycling tests, keeping 80% current after 500 cycles. Above all, the synthesis strategy here is also feasible to fabricate hybrid Co₉S₈–CuS films on various flexible substrates, such as carbon cloth, Ti mesh, and Ni foam for potential applications in wearable energy devices.