A solar cell is an electronic device that converts light directly into electricity through the photovoltaic effect. Its active material is usually a semiconductor, which absorbs incoming radiation and produces electrical charge carriers that can be collected by conductive contacts. Solar cells are the basic generating units of photovoltaic technology: interconnected cells form modules, commonly called solar panels, and modules form larger arrays. Unlike solar-thermal equipment, photovoltaic devices do not require an intermediate conversion of sunlight into heat. (energy.gov)
Operating principle
Light carries energy in discrete packets called photons. When a semiconductor absorbs a suitable photon, an electron can gain enough energy to enter a mobile state, leaving an electron hole that behaves as a positive charge carrier. Generating these carriers is only part of the process: the device must also separate and collect them before they recombine. Selective layers and contacts allow illumination to produce a voltage and drive current through an external circuit. (energy.gov)
Many conventional cells use a p–n junction, formed by joining semiconductor regions with different electrical properties. Doping introduces controlled impurities that alter the populations of electrons and holes. An internal electric field helps separate photogenerated carriers, while metal contacts collect the resulting current. Other architectures use interfaces between different materials and carrier-selective layers to accomplish related functions. (energy.gov)
A semiconductor’s band gap strongly influences which wavelengths it can use. Photons with insufficient energy generally cannot generate an electron–hole pair through ordinary band-to-band absorption. Energy substantially above the absorption threshold is largely dissipated as heat. These spectral losses help explain why a single material cannot convert all incident sunlight into electricity. (energy.gov)
Materials and architectures
Silicon is the most widely used photovoltaic semiconductor. Crystalline-silicon cells are commonly manufactured from thin wafers cut from ingots. Monocrystalline wafers have a single crystal structure, whereas multicrystalline wafers contain multiple crystal grains. Their performance depends not only on crystal quality but also on surface treatment, junction design, and electrical contacts. Surface texturing increases light entry, while protective and passivating layers improve device performance. (energy.gov)
Thin-film photovoltaics use absorber layers deposited on substrates such as glass, metal, or plastic. Established materials include cadmium telluride and copper indium gallium diselenide. Thin-film manufacturing differs from wafer processing: layers can be deposited over large areas and patterned into interconnected cell strips. Organic photovoltaics use carbon-based compounds and can offer flexibility or tunable transparency, although efficiency and operating lifetime remain important constraints. (energy.gov)
Perovskite solar cells employ absorbers with a perovskite-type crystal structure. Their layers can be coated, printed, or vacuum-deposited, but durability and scalable manufacturing are major research challenges. Multijunction cells combine absorbers with different band gaps, allowing successive layers to capture different parts of the solar spectrum. III–V semiconductor multijunction devices are particularly important where high efficiency justifies complex manufacturing, including space applications. (energy.gov)
Performance and efficiency
Conversion efficiency is the fraction of incident optical power delivered as electrical power. Because output depends on both current and voltage, it is evaluated at the operating point that provides maximum power:
Measurements require specified illumination and cell temperature so that results can be compared meaningfully. A current–voltage curve shows how the device responds to different electrical loads; its maximum-power point differs from both the open-circuit and short-circuit conditions. (energy.gov)
Efficiency losses arise from reflected or transmitted light, carrier recombination, and conversion of absorbed energy into heat. Defects and interfaces can provide recombination pathways that reduce collected current. Antireflection coatings and textured surfaces reduce optical losses. Higher operating temperatures generally increase current slightly but reduce voltage more substantially, lowering power output. Cell efficiency therefore does not alone determine the electricity a complete installation delivers over time. (energy.gov)
Manufacturing and system integration
Crystalline-silicon production involves purification, ingot growth, wafer slicing, and cell fabrication. Fabrication typically includes chemical texturing, doping, performance-enhancing coatings, and metallization. During module assembly, cells are electrically interconnected and enclosed between glass and polymer encapsulants, with a backsheet or second glass sheet providing protection. Frames, junction boxes, and cables complete the module assembly. (energy.gov)
Solar cells produce direct current. An inverter converts this output into alternating current for conventional appliances or an electrical grid. Mounting structures support modules, and tracking mechanisms can change their orientation to follow the Sun. Photovoltaic systems can also incorporate batteries, which store generated energy rather than generate it. Building-integrated photovoltaics incorporate modules into roofs, façades, or glazing instead of treating them solely as separately mounted equipment. (energy.gov)
Development and end-of-life management
A major milestone occurred in 1954, when researchers at Bell Labs developed a practical silicon solar cell capable of converting sunlight into substantial electrical output. Subsequent photovoltaic development has focused on increasing efficiency, reducing manufacturing costs, and improving reliability across established and emerging materials. (nokia.com)
End-of-life management concerns complete modules as well as their semiconductor cells. Glass and aluminum account for much of a module’s material content, but separating bonded layers and recovering additional materials complicates recycling. Research includes designs that are easier to dismantle, reduced use of problematic materials, and longer service lifetimes to limit waste before modules are retired. (energy.gov)