Quantitative evaluation of loss mechanisms in thin film solar cells using lock-in thermography

Abstract

We describe the measurement and modeling of lock-in thermograms for three differently processed crystalline silicon on glass thin film silicon solar modules. For the purpose of defect impact evaluation, a bias series of lock-in thermograms for a single cell in each module is measured. The resulting images around maximum power point bias show pronounced Peltier heat redistribution inside the cell, which needs to be taken into account for quantitative evaluation of the thermography results. This is done using a finite differences electronics simulation of the current flow inside the module and convolution of the heat distribution patterns with the thermal blurring. The procedure makes it possible to extract relevant cell performance parameters like the area diode dark saturation current and nonlinear edge shunting current densities as well as to evaluate the relative impact of these on the efficiency under simulated illumination.