Anomalous IV-characteristics of a GaAs solar cell under high irradiance

High irradiance IV-measurements on a CPV GaAs cell with an (Al0.4Ga0.6)0.52In0.48P back surface field revealed some unusual characteristics. With increasing irradiance, an anomaly appeared in the high voltage section of the IV-curve. The anomaly disappeared at sufficiently high temperatures. Because the layer structure of the studied GaAs solar cell is not uncommon, this effect could be more widespread among concentrator cells and is, therefore, of interest to the CPV community. It was demonstrated that the effect is due to a back surface field-related energy barrier and can be avoided by using an Al0.2Ga0.8As back surface field with a higher doping level. The behavior of the anomaly as a function of temperature seems to be in agreement with the mechanism of thermionic emission of current over an internal energy barrier. This mechanism, however, does not explain the irradiance-dependent occurrence of the anomaly.