Thermophotovoltaic Cell Temperature Measurement Issues

The power produced by photovoltaic devices changes with temperature, ranging from 0.1% to nearly 1% per degrees Celsius depending on the structure. The temperature across the surface of TPV cells will vary depending on the amount of absorbed power. Thus the temperature over a region of a wafer where there is no cell will be different from a region of the wafer containing a cell with anantireflection coating and back surface reflector. Vacuum hold-downs or back surface probes may result in local hot spots. Bonding a cell to a heat sink may not be practical in a research environment, and a temperature gradient between the heat sink and space-charge region will still exist. Procedures for determining the current versus voltage (I-V) characteristics at a given temperature arediscussed. For continuous illumination measurement systems, the temperature of the heat sink or backside of the device can be directly measured. The temperature can also be inferred by placing the sample at a known temperature in the dark, and monitoring the open-circuit voltage (Voc) as a high-speed shutter is opened. The maximum Voc from this method corresponds to the temperature in the darkand the plate temperature can then be lowered until this maximum Voc is reached. The temperature can also be indirectly determined from the dark I-V characteristics, assuming negligible series resistance in the ideal case that the voltage in the dark at a given current and temperature corresponds to the Voc and short circuit voltage at that temperature. A high-intensity flash simulator willproduce negligible cell heating during the flash and therefore the cell temperature may be easily set before the flash.