THIN-FILM SOLAR CELLS Technology Evaluation and Perspectives

The main thin-film solar cell technologies are evaluated with respect to the criteria Cost, Applicability, Sustainability and Compatibility with the Dutch PV infrastructure. This evaluation concerns the following technologies in particular: thin film crystalline silicon, separated into low and high temperature deposition processes (LT-f-Si, HT-f-Si), amorphous silicon (a-(Si,Ge):H), copper indium-gallium di-selenide-sulphide (CIGS), cadmium telluride (CdTe) and dye-sensitized (DSC) solar cells technologies. For this evaluation, multicrystalline silicon (mc-Si) is used as a reference. This means that all scores (low, high, etc.) are relative to mc-Si. Organic/polymeric cells are of special interest for the long term, but not enough data is available for a full analysis. Interviews with experts from industry and R&D institutions and a technology review form the basis for this evaluation. The present status, the shortand longterm perspective are reviewed and the risk involved in the further developments is assessed, the risk being separately evaluated and weighed. To facilitate comparison the criteria are quantified and weighing factors are used to normalise the evaluation. Where possible, the developments and data reflect the expected status in 2005. A number of interesting patterns can be observed from this evaluation. In the category Cost, a-(Si,Ge):H, LT-f-Si and DSC score better than mc-Si. In the category Applicability, a-(Si,Ge):H, and to a lesser extent CIGS and CdTe, score high. LT-f-Si scores high for Sustainability, both for its low toxicity content and a high resource availability. CIGS, CdTe and HT-f-Si score low in the categorie Cost, Sustainability and Dutch infrastructure. As expected, only the a-(Si,Ge):H technology scores well on the availability of a good PV R&D infrastructure in The Netherlands. DSC scores relatively high on the R&D infrastructure, where especially the international technological position is excellent. Industrial activities world-wide are concentrated on high-rate and low-cost manufacturing processes. At present industry is investing mainly in the x-Si, a-(Si,Ge):H, CIGS and CdTe technologies. R&D is focused on improving efficiency, gaining a thorough understanding of the material properties and developing new deposition techniques. The interviews with experts indicate confidence in x-Si and a-(Si,Ge):H technologies with regard to the criteria Costs, Efficiency and Risk control. The technology mapping confirms these expectations. A major difficulty in scaling up the CIGS and CdTe technologies is the control of active layer deposition over a large area. The critical risks involved in processing LT-f-Si technologies are the deposition of the active layer and control of the material properties. The a-(Si,Ge):H and LT-f-Si are strongly related and it is expected that they can benefit from each other, with mutual spin-off’s and probably combined devices. HT-f-Si has a potential for high efficiencies, but the development time is still long and no real successful deposition process has been identified yet, so the level of uncertainty is high. It is anticipated that the dyesensitised and the organic/polymeric solar cells will become important in the midto longer term with advantages in Costs and Applicability. Much basic and applied research has yet to be done on the stability for both types and the charge transport properties of organic/polymeric materials. During the interviews, several experts mentioned that more co-operation between research groups and the industry is important on a European and intercontinental level.