Dye solar cells (DSCs) consist typically of two conductive glass plates in which the three main active components of the cell are sandwiched: a dye that strongly absorbs light from the sun, a titanium dioxide (TiO2) layer and an electrolyte which transport the electric charges across the cell.
The dye molecules are anchored to the TiO2 layer which is deposited in such a way to form a nanostructured porous film in order to greatly increase the area onto which the dye can attach itself. Dye molecules are photo-excited by the incoming light. TiO2 conduction levels are such that the electronic charges produced by the excitation of the dye are rapidly and efficiently transferred from the dye to the TiO2 and transported to the one of the electrodes. The electrolyte, after extracting charge from the other electrode, refurnishes the dye with the electron it has just lost to the TiO2. No permanent chemical transformation occurs during this basic process. In this way, the dye solar cell manages to continually transform light from the sun into electric current and energy once a load (e.g. an electrical appliance) is applied between the two terminals.
Dye solar cell technology has great potential to deliver low-cost photovoltaic modules. The photoactive material components of the cell are attractive because they can generally be processed over large areas from liquid solution or pastes using lowcost, relatively low-temperature deposition and processing techniques. The technology permits in principle a direct up-scaling from the single cell to the module as it becomes possible to create series and parallel interconnections of cells without the need of external connections as happens in conventional crystalline semiconductor technology. Production of solar modules is essential as appliances need set voltages that cannot be met by a single cell. To avoid rapid degradation of cell performance and in order to withstand the lifetime requirements of most applications, a careful choice of combination of materials and stringent encapsulation of the photoactive materials from the environment are necessary. One of the main objectives of C.H.O.S.E is the study and development of complete fabrication techniques at the cell and module level (see Figure) on both glass and flexible substrates. In this, C.H.O.S.E is aided by the collaborations set up with a variety of partners especially regarding the development of materials for DSCs.
