Analysis techniques for amorphous silicon solar cells

The dependence of photocurrent (Iph) on voltage (V) and light intensity (ø) in p-i-n a-Si solar cells was studied, showing flatband voltage (Vfb) and conversion efficiency to increase with ø. To isolate the i-layer properties, we utilized Crandall´s uniform-field collection efficiency model and tested its applicability limits. We found that p-layer properties and p-i interface can affect the fill factor (FF). Behavior of I(V) curves near the maximum power point (MPP), however, was not well-described by the model, leading us to propose a new metric: the MPP curvature of the I(V) curve normalized to I=1, V=1 at MPP (MPP K). Simulated and measured data show no unique relationship between FF and MPP K. Our analysis reveals that gradients in cross-flow PECVD growth chamber and the choice of transparent conductive oxide (TCO) substrates can affect i-layer properties and the overall quality of p-i-n solar cells.