A dual-function photoelectrochemical solar cell which assimilates light-harvesting, charge-transport and photoelectrochromic nanomaterials in a tandem design

A multifunctional tandem cell has been fashioned by (i) replacing the conventional counter electrode in a n-type titanium dioxide-based quantum dot sensitized solar cell (QDSC) with a QD-sensitized p-type nickel oxide photocathode to harness maximum power-conversion efficiency, and (ii) by coating an electrochromic molybdenum oxide overlayer at the photoanode. Light harvesting In2S3 nano-flakes were deposited onto a mesoporous NiO semiconductor scaffold. On pairing with the n-QDSC, substantial gains in the photovoltaic performance were achieved owing to greater spectral utilization across the visible region. Improvements to the photoanode architecture were developed by embedding plasmonic Au NPs in the CdS QD-sensitized TiO2 layer to augment the light absorption via plasmonic and scattering effects which translated to higher photocurrent densities. A thin film of MoO3 was applied to the photoanode, which provided an electrochromic response upon illumination, due to the concurrent insertion of an electron and a cation in the MoO3 matrix. The power conversion efficiency (PCE) achieved was 6.01% for the n-QDSC half-cell (TiO2/CdS/Au/MoO3-nS2−/Sn2−-C-fabric) and 0.047% for the p-QDSC half-cell (NiO/In2S3-nS2−/Sn2−-C-fabric). A stellar PCE value of 7.99% was attained when the two half-cells were co-assembled in a tandem device, in spite of the disparity in performance between the photoanode and photocathode. The maximum transmission modulation for the tandem device under 1 sun irradiance was 34% and the photocoloration efficiency was 16.4 cm2 min−1 W−1 at 550 nm. The results highlight the potential opportunities for combining energy conversion and light management in photovoltaics based on nanotechnology.