Thin - film solar cell technologies based on Si with a thickness of less than a fewmicrometers combine the low - cost potential of thin - film technologies with the advantagesof Si as an abundantly available element in the earth's crust and a readily manufac -turable ma te rial for photovoltaics (PVs). In recent years, several technologies have beendeveloped that promise to take the per form ance of thin - film silicon PVs well beyond thatof the currently established amorphous Si PV technology. Thin - film silicon, like no otherthin - film ma te rial, is very effective in tandem and triple - junction solar cells. The researchand development on thin crystalline silicon on foreign substrates can be divided intotwo different routes: a low - temperature route compatible with standard float glass or evenplastic substrates, and a high - temperature route (☻600♥C). This ar ticle reviews the ma te -rial properties and technological challenges of the different thin - film silicon PV ma te rials.