Photothermal Measurement of Minority Carrier Diffusion in Devices

Abstract

By refining a photothermal method developped earlier for analyzing electronic carrier- and thermal fluxes in photovoltaic cells, photothermal data on single crystal Si solar cells are obtained that show, already at rather low modulation frequencies, the effects of electronic carrier diffusion in the base. Thus, these methods are able to examine actual transport properties, in addition to their use for characterizing devices, (by separation of photogenerated and injected carrier-mediated processes). Thermal diffusion and diffusion of minority carriers influence the experimental results of measurements, obtained with spatial separation by varying the distance between the area of photo-excitation and detector area. The data are analyzed by generalization of the model developped for electronic carrier and energy flow in solar cells. This is done by solving the coupled thermal diffusion/carrier diffusion equation.