Quasi solid-state photoelectrochemical cells combining nanocomposite semiconductors

Exploitation of the incoming solar energy is more than adequate to sufficiently meet the energy demands of the modern world. Photovoltaics constitute devices that convert solar energy to electricity. Among them, silicon photovoltaics have been extensively studied, although an emphasis has been given in the last decades towards third generation photovoltaics, such as dye sensitized solar cells (DSSCs). DSSCs are made of materials based on nanostructured semiconductors as photoanodes, with low cost and transparency. The main semiconductor that has been widely studied is titanium dioxide (TiO₂), however the rate of electron recombination blocks the extensively high conversion efficiency. Many attempts have been made in order to suppress these losses and improve electron transport. Remarkable efforts led to doping the electrodes or combining specific semiconducting metal oxides with desirable band gaps in order to improve the direct electron transport, and eliminate electron recombination. At the present work, we demonstrate a combination of semiconductors (TiO₂, In₂O₃, with band gaps about 3.2eV and 3eV respectively), where In₂O₃ acts as a barrier layer that suppresses the back reaction (recombination) and accelerates the electron transport, leading to higher charge collection efficiency. The photoanode was fabricated by TiO₂ underlayer and In₂O₃ top layer due to the deeper conduction band of TiO₂ than that of In₂O₃. Solar cells were fabricated combining these photoanodes with quasi solid-state electrolyte based on I-/I3- redox couple. The structural properties of the films with combined semiconductors were examined with porosimetry methods and scanning electron microscopy. The performance of the DSSCs with negative photoelectrodes made with combined TiO₂-In₂O₃ oxides proved to be higher compared with those obtained for one semiconductor. 17% maximum increase to the overall performance was monitored for DSSCs made with TiO₂-In₂O₃ coupled semiconductors in contrast to the pure TiO₂ films.