High-efficiency counter electrodes for quantum dot-sensitized solar cells (QDSSCs): designing graphene-supported CuCo 2 O 4 porous hollow microspheres with improved electron transport performance.

Owing to it being low-cost and eco-friendly and having multiple oxidation states, the ternary transition metal oxide CuCo 2 O 4 has been used as an electrode material with superior electrocatalytic activity in numerous fields. However, its application in quantum dot-sensitized solar cells (QDSSCs) has not been investigated. Herein, we synthesized porous hollow micro-spherical CuCo 2 O 4 nanomaterials by simple solvothermal and calcination processes and then applied them in QDSSCs as counter electrodes (CEs). Because of the low density, good shell permeability of the hollow porous structure and high catalytic activity of the material, QDSSCs achieved a higher efficiency of 6.19%. Furthermore, considering the structural flexibility, large specific surface area and high conductivity of graphene, CuCo 2 O 4 /RGO composites were further prepared. QDSSCs equipped with optimized CuCo 2 O 4 /RGO 12 CEs achieved a power conversion efficiency (PCE) of up to 7.04% with J sc = 22.83 mA cm -2 , V oc = 0.61 V, and FF = 0.51, which is higher than that of the pure CuCo 2 O 4 CE. Both EIS and the Tafel test proved that the CuCo 2 O 4 /RGO 12 CE has the best catalytic activity and electron transport performance, which is beneficial for the regeneration of the S 2- /S n 2- redox couple. The prominent cell performance mainly depends on the combination of the abundant catalytically active sites of CuCo 2 O 4 and the excellent conductivity and structural flexibility of graphene.