Role of HA additive in quantum dot solar cell with Co[(bpy)3]2+/3+-based electrolyte

Abstract

A strategy to improve the power conversion efficiency (η) in a quantum dot solar cell (QDSC) is demonstrated with a model system of TiO₂/CdS QDSCs. When the electrolyte is changed from polysulfide to a [Co(bpy)₃]^2+/3+ complex, a higher V_oc and η are observed because of its low redox potential. To resolve the slow diffusion nature of [Co(bpy)₃]^2+/3+ complexes within dense TiO₂ nanoparticle/CdS film, a TiO₂ nanorod (NR) array anode is applied, which increases η by more than a factor of 3. In addition, introduction of hexanoic acid (HA) in TiO₂ NR/CdS film is found to improve η (J_sc as well as V_oc) by alleviating the back recombination loss between Co^III and the TiO₂ surface. Electrochemical impedance spectroscopy indicates that the charge transfer resistance on the photoanode decreases by suppressing the interfacial charge recombination after HA treatment, although adding HA in the electrolyte impedes diffusion resistance.