Carrier Diffusion Imaging of a Thin Silicon Solar Cell
As the demand and necessity for more reliable renewable energy sources increases, more research is needed to ensure that new products which reach the market are as efficient as they can be. Photovoltaics research focuses on characterizing and improving the efficiency of solar cells. A major source of valuable information in photovoltaics research is the charge-carrier lifetime, a measure of how quickly the charge carriers recombine and stop producing electrical energy. We employ a new technique to measure the carrier lifetime, by direct imaging of the solar cell in action. An IR camera was used to image a thin Silicon sample illuminated by a 532 nm laser, in turn releasing charge carriers radially outwards. Our goal was to capture the diffusion of charge carriers and use the camera to analyze the minute temperature differences created on the sample as a result. By modulating the laser, we can look at the effect of varying frequencies on the amplitude of the signal produced by the diffusing charge carriers. Fitting a known relation to this allows us to extract the lifetime from the direct imaging of the cell. Using this technique, we were able to measure a lifetime of ~20 µs, which is well within the range for the sample used.