What Are Photovoltaic Cells?

Photovoltaic (PV) cells are semiconductor devices that convert sunlight directly into electricity through the photovoltaic effect, first described by Edmond Becquerel in 1839. When photons strike a semiconductor material with sufficient energy, they excite electrons across the material's bandgap, generating an electric current. This mechanism, grounded in quantum mechanics and solid-state physics, underpins the global solar energy industry, which installed over 390 gigawatts of new capacity in 2023 alone. PV cells operate without moving parts, produce no direct emissions, and can be manufactured at scales ranging from milliwatt flexible patches to gigawatt utility installations.

The P-N Junction

Nearly every photovoltaic cell is built around a p-n junction, formed by joining p-type semiconductor material (doped to create positive charge carriers) with n-type material (doped to create negative charge carriers). The junction establishes a built-in electric field that separates photogenerated electron-hole pairs before they recombine. This charge separation is what drives current through an external circuit. The quality of the junction, including its defect density and interface passivation, determines how efficiently the cell converts absorbed photons into usable electricity. Minority carrier lifetime, a measure of how long excited electrons survive before recombining, is one of the most diagnostically important parameters in cell characterization.

Silicon Solar Cells and Light Trapping

Silicon remains the dominant PV material, accounting for more than 95 percent of global module shipments. Monocrystalline silicon cells achieve the highest efficiencies among commercial products, with record laboratory values exceeding 26 percent for single-junction devices, as documented in the NIST photovoltaic calibration program. Multicrystalline silicon offers lower material costs at a modest efficiency penalty.

Light trapping is a central design challenge in silicon cells because silicon is an indirect bandgap semiconductor with relatively weak optical absorption. Engineers address this through surface texturing (typically alkaline etching that produces pyramid-like microstructures), anti-reflection coatings, and rear-side reflectors. These features extend the effective optical path length inside the cell, allowing thinner wafers to absorb nearly as much light as thicker ones, reducing material cost without sacrificing photocurrent.

Thin-Film and Multi-Junction Cells

Thin-film technologies deposit semiconductor layers only a few micrometers thick onto glass, metal foil, or polymer substrates. Cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) are the leading commercial thin-film platforms, offering lower manufacturing energy and the ability to integrate into building facades and flexible surfaces. Although their efficiencies trail silicon in most comparisons, thin-film modules maintain better performance at elevated temperatures, an important advantage in hot climates.

Multi-junction cells stack multiple sub-cells tuned to different portions of the solar spectrum. Each sub-cell absorbs a specific wavelength range, so the combined stack captures a broader fraction of incident solar energy than any single junction could. Concentrator photovoltaic systems using III-V multi-junction cells have demonstrated efficiencies above 47 percent under concentrated light, as reported by researchers publishing in Progress in Photovoltaics. These devices are used in space power systems and high-concentration terrestrial applications where optics focus sunlight onto small cell areas.

Perovskite Solar Cells

Perovskite solar cells, named for their ABX3 crystal structure, emerged as a research focus after 2012 and have shown a pace of efficiency improvement unmatched in the history of PV. Their tunable bandgap, low-temperature processability, and high defect tolerance make them attractive for both standalone and tandem configurations. Perovskite-silicon tandem cells have surpassed 33 percent certified efficiency, as tracked in the NREL Best Research-Cell Efficiency Chart. Durability under moisture, heat, and ultraviolet exposure remains the primary barrier to commercialization.

Applications

• Utility-scale solar farms connected to the grid
• Rooftop systems for residential and commercial buildings
• Satellite and spacecraft primary power
• Off-grid rural electrification and water pumping
• Consumer electronics including calculators, wearables, and IoT sensors
• Building-integrated photovoltaics in windows, facades, and roofing materials