Spatially resolved trap spectroscopy in amorphous silicon solar cells

A new method to extract information about the spatial distribution of the density of defect states in the intrinsic layer of an amorphous silicon solar cell from capacitance measurements is presented. Forward bias capacitance measurements are shown to be strongly sensitive to the spatial distribution of defects in the i-layer of the p-i-n device, and thus they are suitable to be used as a powerful tool to detect the presence and the extension of nonuniformity, for example, the damaged zone near the doped layer. In this work, the authors develop a fit algorithm to extract the DOS (density of states) distribution from capacitance measurements. They use the 'double carrier model', which is an analytical description of both majority and minority carrier distributions in the p-i-n structure, together with SHR theory on trapping to develop the model of the capacitance. A set of capacitance measurements performed at different forward bias, frequency and temperature is taken in order to minimize measurement error. DOS is obtained by a simplex optimization procedure. Preliminary results of the fitting algorithm are presented. >