Thin-film solar cell

Thin-film solar cells emerged from a surprising discovery: amorphous (non-crystalline) silicon could be doped with impurities just like crystalline silicon, opening a path to dramatically cheaper solar energy. In 1975, Walter Spear and Peter LeComber at Dundee University discovered that hydrogenated amorphous silicon (a-Si:H) could be doped with boron and phosphorus to create p-type and n-type semiconductors. Within a year, the first amorphous silicon solar cells were demonstrated with 2.4% efficiency.

The economic logic was compelling. Crystalline silicon solar cells required expensive single-crystal or polycrystalline wafers, grown at high temperatures from ultra-pure silicon. Thin films could be deposited on cheap substrates—glass, metal, plastic—at lower temperatures using less material. The manufacturing process resembled semiconductor fabrication: large-area deposition, rapid throughput, potential for dramatic cost reduction.

By 1986, the first commercial thin-film technologies reached market. ARCO Solar and others deployed amorphous silicon panels, finding initial success in small applications—calculators, watches, consumer electronics. The low power requirements and flexible form factors suited these niches perfectly. But a-Si thin films suffered from fundamental limitations: low efficiency (around 6-8%) and the Staebler-Wronski effect, a degradation under light exposure that reduced output over time.

Alternative thin-film materials emerged to address these weaknesses. Research into cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) began in the 1980s. Harold McMaster founded Solar Cells Incorporated (later First Solar) to pursue CdTe, attracted by its 1.4 eV bandgap that matched the solar spectrum optimally. After initial struggles—7% efficiency, production setbacks—First Solar reached commercial scale in 2002. By 2024, CdTe panels achieved over 22% efficiency and First Solar became the only U.S. manufacturer competing with Chinese crystalline silicon producers.

The thin-film story illustrates how multiple technological lineages can compete within a single problem space. Amorphous silicon dominated early markets, then stalled. Cadmium telluride emerged as the commercial winner. CIGS found aerospace and specialty applications. The cheapest solar technology in 2025 remains crystalline silicon—path dependence from decades of manufacturing scale—but thin films carved out niches where flexibility, weight, or aesthetics matter.