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13 November 2008


Dual-junction PV efficiency record raised to 32.6%

The III-V Semiconductors group of the Instituto de Energía Solar at Universidad Politécnica de Madrid (IES-UPM) in Spain has set a new record for solar energy conversion efficiency of 32.6% for a dual-junction photovoltaic cell.

Designed and fabricated on a GaAs substrate in a horizontal MOCVD reactor by IES-UPM’s III-V Semiconductors group, the lattice-matched GaInP/GaAs dual-junction solar cell was independently measured at the calibration laboratory of the Fraunhofer Institute for Solar Energy Systems (FhG-ISE) in Freiburg, Germany. The 32.6% efficiency was measured under light concentration of 1026 suns (where one sun is the amount of light that typically hits the Earth on a sunny day), while at 2873 suns the efficiency is still 31.1%. Professor Carlos Algora, director of the III-V Semiconductors group, says that the new cell is an important advance for terrestrial concentrated photovoltaic (CPV) modules, which use lenses or mirrors to focus sunlight onto the solar cells.

IES-UPM says that its new solar cell differs significantly from the previous record holder, made by Fraunhofer ISE (which, in 2000, achieved 31% at 300 suns). It adds that the importance of the new record is not only the efficiency increase of 1.6%, but also the concentration level (1026 suns versus 300 suns). As a rule of thumb, the higher the concentration, the lower the resulting price of the generated electricity. IES-UPM reckons that, after about five years of development, the cost of solar electricity from CPV systems based on this type of solar cell would be about 5.5c€/kWh, while at present the cost of electricity in Spain (generated by all available sources: nuclear, oil, coil, gas, renewable etc) is about 7.5c€/kWh.

Algora stresses that this record dual-junction solar cell represents a step towards improving the efficiency of triple-junction solar cells, for which the efficiency record of 40.8% was achieved under concentration of 300 suns by the US National Renewable Energy Laboratory (NREL). Researchers in the IES-UPM’s III-V Semiconductors group think that integration of its dual-junction structure into a triple-junction solar cell could result in a device with efficiencies of more than 41% at 1000-sun concentration.

See related items:

Fraunhofer ISE raises Euro PV efficiency record to 39.7%

NREL sets solar cell efficiency record of 40.8%

IMEC claims record 24.7% efficiency for single-junction GaAs-on-Ge solar cell

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