THIN-FILM SILICON SOLAR-CELLS - A REVIEW AND SELECTED TRENDS

A case is developed for considering silicon as the prime medium-term candidate for semiconductor photovoltaic cells; the argumentation is based on other materials not being abundantly available, highly toxic and/or very expensive. Crystalline silicon solar cells have excellent efficiencies, however, according to data presented by the authors on material fluxes and energy consumption there are serious bottlenecks for this technique with respect to future large-scale applications both from an economical as well as from an ecological point of view. Thus, the authors consider thin-film silicon solar cells as the main option for large-scale energy applications in the foreseeable future. Thin-film silicon solar cells are either polycrystalline or amorphous. The first category is gaining in interest at this moment, but major technological problems remain unresolved, e.g., growth of a high-quality crystalline structure on foreign (low-cost) substrates, reduction of deposition temperature and increase of deposition rate. The second category has so far yielded only limited stable efficiencies, although progress has been recently achieved in improving the stability of solar cells using stacked or tandem/triple structures. Novel approaches to further improve the stable efficiencies, such as using low-level doping profiles within the i-layer of the p-i-n solar cell, are listed. Entirely microcrystalline p-i-n solar cells that are stable and can be deposited at low temperatures (220 degrees C) with rates up to 1 Angstrom/s by the VHF plasma deposition technique are described as further, recent contribution to thin-film silicon photovoltaic technology.