An insight in photocurrent generation mechanism on Cu2O quantum dot sensitized Cu/p-CuI photo-electrochemical cell and efficient H2 generation at Cu/p-CuI/Cu2O electrolyte interface

Abstract

p-CuI (band gap ≈ 3.1 eV) is sensitised with quantum dots (QDs) of Cu2O (band gap ≈ 2.0 eV) as a novel hybrid strategy to make photoelectrochemical cells. In which, p-CuI thin film was deposited by immersing a cleaned copper sheet into a solution containing I2 (10−2 M), KI (0.1 M), CuSO4 (10−3 M) to make Cu/p-CuI photoelectrodes. To fabricate Cu/p-CuI/Cu2O photoelectrodes, Cu/p-CuI photoelectrodes were boiled in a CuSO4 (10−2 M) solution at different time intervals. When gradually increases the boiling time until 5 min, the size of the p-CuI microcrystals decreases with the formation of Cu2O QDs on p-CuI microcrystals. When the boiling period exceeds 5 mins, Cu2O QDs convert gradually into micro-crystals and covering p-CuI thin film. Variations in the photocurrent quantum efficiency (Φ%) with the Cu2O amount fabricated on p-CuI thin layer were monitored. The photophysical and photochemical processes associated at Cu/p-CuI/Cu2O-electrolyte interface are presented to delineate the sensitisation of p-CuI wide band gap semiconductor with Cu2O QDs produced. Our recent explanation on the kinetics of the photocurrent generation by dye sensitised solar cells using CAN’s model equation Φ = AD0 – BD02, was used to describe the QD sensitisation of p-CuI by Cu2O QDs. It was experimentally confirmed that CAN’s constant ‘A’ relates with the photocurrent generation processes and the CAN’s constant ‘B’ associated with the processes in suppression of photocurrent generation. Material characterisation from Scanning Electron Microscopy (SEM), Field Emission Scanning Electron Microscopy (FESEM), X-ray Diffraction (XRD), UV absorption, photocurrent action spectra, and photoelectrochemical (PEC) measurements through I-V characteristics are presented to confirm the formation of Cu/CuI/Cu2O electrodes. A remarkable H2 generation was noticed in the presence of 0.025 M Na2SO4 solution, from the QDs sensitised photogenerated electrons at Cu/p-CuI/Cu2O-electrolyte interface. The mechanism of H2 generation is confirmed with the energy band positions of p-CuI and Cu2O QDs under visible light irradiation. Different H2 profiles are presented in detail with the size of QDs fabricated on p-CuI.