Colour-Tuneable Hybrid Heterojunctions as Semi-Transparent Photovoltaic Windows for Photoelectrochemical Water-Splitting

The strong but narrow-bandwidth absorption spectra of organic semiconductors make them excellent candidates for semi-transparent solar-cell applications in which colour-specificity is important. In this mainly theoretical study, we show that using a hybrid heterojunction combining the transparent inorganic semiconductor CuSCN with organic semiconductors (C70, PC70BM, C60, ITIC, IT-4F or Y6), simple colour-tuneable solar cells in which the transmission spectrum is determined solely by the choice of the organic semiconductor can be fabricated. Using a joint electrical-optical model, we show that it is possible to combine the unique attributes of high photovoltage and colour tunability to use these heterojunctions as photovoltaic windows in tandem photoelectrochemical (PEC) -photovoltaic (PV) cells. We demonstrate that this configuration can lead to a reduction in the parasitic absorption losses in the PEC-PV and thus to solar-to-hydrogen efficiencies (>3%) that are higher than that predicted using the traditionally used architecture in which the PV is placed behind the PEC.