Evaluation of solar cell performance by photothermal spectroscopy

A photothermal spectrometer (PTS) was assembled to detect temperature changes in solar cells when they absorbed the light energy. It has been used to determine the performance of an amorphous silicon solar cell and the quality of the data is compared with those obtained by the conventional electrical measurement. The spectral response of energy conversion and quantum efficiencies have been derived by measuring the temperature change in a solar cell which is connected to a variable load and periodically exposed to monochromatic light. By this relatively simple method, efficiencies inherent to the cell material and junction structure, i.e. efficiencies without including such a loss as the light reflection at the cell surface, can be evaluated even if the exact light intensity is unknown. The efficiencies observed by PTS was actually a little higher than the efficiency determined by the conventional I-V measurement. Validity and problems of the method are discussed with special emphasis on the improvement in response and sensitivity of PTS by using thin film thermisters or infrared light sensors.