Thermophotovoltaic Cell Temperature Measurement Issues Page: 3 of 13
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Thermophotovoltaic Cell Temperature
T. Moriarty and K. Emery
NREL, 1617 Cole Blvd., Golden, CO, 80401
Abstract. 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 contain-
ing a cell with an antireflection 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 are discussed. For continuous illumination measurement systems, the tempera-
ture 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 (V ) as a high-speed shutter is opened. The maximum V from this method corre-
sponds to the temperature in the dark and the plate temperature can then be lowered until this
maximum V 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 V and short circuit voltage (I) at that tempera-
ture. A high-intensity flash simulator will produce negligible cell heating during the flash and
therefore the cell temperature may be easily set before the flash.
Many thermophotovoltaic (TPV) device performance parameters, and hence overall
power output, vary with device space-charge region temperature. As with any photovol-
taic device, it is important to quantify these variations in the form of temperature coeffi-
cients for the essential current versus voltage (I- V) parameters. It is even more impor-
tant for TPV devices because they are likely to be tested and operated in harsh conditions
at elevated temperatures and with large temperature gradients. This paper discusses
some difficulties in measuring TPV device temperatures under testing conditions, con-
sequences of inaccurate temperature measurements, methods for mitigating the difficul-
ties, and temperature coefficients for the open-circuit voltage (V c), maximum power
(Pm), fill factor (FE), and the short-circuit current (I) for a InGaAs TPV device fabri-
cated at NREL with an energy gap of 0.6 eV.
presented at the 4th NREL Conference on Thermophotovoltaic Generation of Electricity, Denver, CO, Oct. 11-14, 1998
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Emery, K. & Moriarty, T. Thermophotovoltaic Cell Temperature Measurement Issues, article, November 13, 1998; Golden, Colorado. (digital.library.unt.edu/ark:/67531/metadc620919/m1/3/: accessed November 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.