Solar-cell efficiency

Solar-cell efficiency is the portion of energy in sunlight that is converted into electricity by a solar cell. Efficiency, in combination with latitude and weather, determine the energy output of a solar system. As of 2024, the record for solar cell efficiency was 47.6%, set in May 2022 by Fraunhofer ISE, with a III-V four-junction concentrating photovoltaic (CPV) cell. The record in real-world conditions is held by NREL, which developed triple junction cells with a tested efficiency of 39.5%. Commercial solar modules may exceed 24% efficiency. As of 2025, the best reached 24.5%, typically lower than their cells in isolation. The most efficient mass-produced solar modules have power density values of 175 W/m2 (16.22 W/ft2). In 2026 using triple III-V germanium cells and shingled matrix technology to interconnect cells, Fraunhofer achieved efficiency of 34.4%. An important innovation was the use of direct cell-to-cell contact, eliminating traditional solder-coated copper ribbons and the resulting shading of active cell areas.

Several factors affect conversion efficiency, including its reflectance, thermodynamic efficiency, charge carrier separation efficiency, charge carrier collection efficiency and conduction efficiency values. Because these parameters are difficult to directly measure, other parameters are measured instead, including quantum efficiency, open-circuit voltage (VOC) ratio, and § Fill factor. Reflectance losses are accounted for by the quantum efficiency value, as they affect external quantum efficiency. Recombination losses are accounted for by these factors. Resistive losses are predominantly accounted for by the fill factor value, but also contribute to the others. Depending on construction, photovoltaic modules can produce electricity from a range of frequencies of light, but usually cannot cover the entire solar radiation range (specifically, ultraviolet, visible, infrared and low or diffused light). Hence, much of the incident sunlight energy is not processed by solar modules. Theoretically, sunlight could be split into wavelength bands (each a different color), each directed onto cells tuned to those ranges that would convert that band more efficiently.

History Until 2024 the record was 47.1%, set in 2019 by multi-junction concentrator solar cells developed at National Renewable Energy Laboratory (NREL), Golden, Colorado, USA, which was set in lab conditions, under extremely concentrated light. In early 2026, Fraunhofer ISE announceed a 34.2% efficient 883 cm2 (136.9 sq in) module. The module used triple III-V germanium cells. The unit was an adaptation of its space cell to the terrestrial solar spectrum.

Factors affecting energy efficiency The factors affecting energy conversion efficiency were expounded in a landmark paper by William Shockley and Hans Queisser in 1961. See Shockley–Queisser limit for more detail.

Thermodynamic-efficiency limit and infinite-stack limit

If one has a source of heat at temperature Ts and cooler heat sink at temperature Tc, the maximum theoretically possible value for the ratio of work (or electric power) obtained to heat supplied is 1-Tc/Ts, given by a Carnot heat engine. If we take 6000 K for the temperature of the sun and 300 K for ambient conditions on earth, this comes to 95%. In 1981, Alexis de Vos and Herman Pauwels showed that this is achievable with a stack of an infinite number of cells with band gaps ranging from infinity (the first cells encountered by the incoming photons) to zero, with a voltage in each cell very close to the open-circuit voltage, equal to 95% of the band gap of that cell, and with 6000 K blackbody radiation coming from all directions. However, the 95% efficiency thereby achieved means that the electric power is 95% of the net amount of light absorbed – the stack emits radiation as it has non-zero temperature, and this radiation must be subtracted from the incoming radiation when calculating the amount of heat being transferred and the efficiency. They also considered the more relevant problem of maximizing the power output for a stack being illuminated from all directions by 6000 K blackbody radiation. In this case, the voltages must be lowered to less than 95% of the band gap (the percentage is not constant over all the cells). The maximum theoretical efficiency calculated is 86.8% for a stack of an infinite number of cells, using the incoming concentrated sunlight radiation. When the incoming radiation comes only from an area of the sky the size of the sun, the efficiency limit drops to 68.7%.

Ultimate efficiency Normal photovoltaic systems however have only one p–n junction and are therefore subject to a lower efficiency limit, called the "ultimate efficiency" by Shockley and Queisser. Photons with an energy below the band gap of the absorber material cannot generate an electron-hole pair, so their energy is not converted to useful output, and only generates heat if absorbed. For photons with an energy above the band gap energy, only a fraction of the energy above the band gap can be converted to useful output. When a photon of greater energy is absorbed, the excess energy above the band gap is converted to kinetic energy of the carrier combination. The excess kinetic energy is converted to heat through phonon interactions as the kinetic energy of the carriers slows to equilibrium velocity. Traditional single-junction cells with an optimal band gap for the solar spectrum have a maximum theoretical efficiency of 33.16%, the Shockley–Queisser limit. Solar cells with multiple band gap absorber materials improve efficiency by dividing the solar spectrum into smaller bins where the thermodynamic efficiency limit is higher for each bin.

Quantum efficiency

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