Operando Temperature Measurements of Photovoltaic Laser Power Converter Devices Under Continuous High-Intensity Illumination

Photovoltaic devices that operate under extremely high irradiances, such as laser power converters (LPCs), may also operate at elevated temperatures, even under active cooling, as the result of large temperature gradients. We demonstrate the operation of GaAs LPC devices under orders of magnitude of irradiances up to 150 W/cm2 in a monochromatic laser simulator with an active cooling stage. The steady-state open-circuit voltage (VOC) as a function of irradiance is known to droop at high irradiance as the result of junction heating, but the junction temperature can be difficult to measure by conventional methods. Fast, transient VOC measurements under these extreme operating conditions are used here to determine the junction temperature. Empirical VOC temperature coefficients of the devices at each irradiance of interest are determined and used as an integral part of this technique. We show that the thermal design of different LPC devices strongly affects the operating temperature of the junctions. Knowledge of the operating temperature can be a strong tool for understanding the nature of loss mechanisms and improving the design for the operation of photovoltaic LPCs at high irradiances. This technique can be used for laboratory devices during initial design as well as to characterize mass-produced and packaged devices for quality control.