Current flow and potential efficiency of solar cells based on GaAs and GaSb p-n junctions

• Published in: Semiconductors (Woodbury, N.Y.) Vol. 43; no. 5; pp. 644 - 651
• Main Authors: Andreev, V. M., Evstropov, V. V., Kalinovsky, V. S., Lantratov, V. M., Khvostikov, V. P.
• Format: Journal Article
• Language: English
• Published: Dordrecht SP MAIK Nauka/Interperiodica 01.05.2009
• Subjects: EFFICIENCY; ELECTRIC CURRENTS; ELECTRON BEAMS; GALLIUM ANTIMONIDES; GALLIUM ARSENIDES; ILLUMINANCE; IRRADIATION; LUMINESCENCE; Magnetic Materials; Magnetism; MATERIALS SCIENCE; MEV RANGE 01-10; P-N JUNCTIONS; Physics; Physics and Astronomy; Physics of Semiconductor Devices; PROTON BEAMS; SOLAR CELLS; SOLAR RADIATION; TUNNEL EFFECT; 78.55.Cr; 85.30.Kk; 84.60.Jt; 73.40.Kp
• ISSN: 1063-7826; 1090-6479
• DOI: 10.1134/S1063782609050200

Dependence of the efficiency of single-junction and multijunction solar cells on the mechanisms of current flow in photoactive p-n junctions, specifically on the form of the dark current-voltage characteristic J-V , has been studied. The resistanceless J-V j characteristic (with the series resistance disregarded) of a multijunction solar cell has the same shape as the characteristic of a single-junction cell: both feature a set of exponential portions. This made it possible to develop a unified analytical method for calculating the efficiency of singlejunction and multijunction solar cells. The equation relating the efficiency to the photogenerated current at each portion of the J-V j characteristic is derived. For p-n junctions in GaAs and GaSb, the following characteristics were measured: the dark J-V characteristic, the dependence of the open-circuit voltage on the illumination intensity P-V OC , and the dependence of the luminescence intensity on the forward current L-J . Calculated dependences of potential efficiency (under idealized condition for equality to unity of external quantum yield) on the photogenerated current for single-junction GaAs and GaSb solar cells and a GaAs/GaSb tandem are plotted. The form of these dependences corresponds to the shape of J-V j characteristics: there are the diffusion- and recombination-related portions; in some cases, the tunneling-trapping portion is also observed. At low degrees of concentration of solar radiation ( C < 10), an appreciable contribution to photogenerated current is made by recombination component. It is an increase in this component in the case of irradiation with 6.78-MeV protons or 1-MeV electrons that brings about a decrease in the efficiency of conversion of unconcentrated solar radiation.