Analysis of Amorphous Silicon Solar Cells by the Photocurrent-Separation Method

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Abstract
A simple but profitable analysis of amorphous silicon (a-Si) solar cells is conducted. The analysis is based on the principle of separating the output current I out(V) into the dark current I d(V) and photocurrent I ph(V). The illumination-intensity dependence of I out(V) can be calculated in the wide range of illumination intensities (from 1.1×10-2 to 5.1×102 mW/cm2 in this study), even if the effects of series and/or shunt resistance are considerable. The output current is also investigated in relation to the design of multi-junction cells. I out(V) of multi-junction cells can be simulated precisely by separating the I out(V), both before and after light soaking. The estimation of cell parameters from the separated I ph(V) is also investigated. I out(V) can be expressed by a relatively simple formula using only two fitting parameters: the mobility-lifetime products (µτ) and built-in potential of the junction (V t). Good agreement between the results of the experiments and the calculations in this study suggests that the basic concept of the analysis, i.e. I out(V) can be separated into I d(V) and I ph(V), is valid.