Nonuniform degradation and hot spots in thin film PV

Patterns of efficiency degradation in thin film PV reveal noticeable variations between nominally identical cells. This and some other observations point at laterally nonuniform degradation driven by weak spots on a cell. These spots can be either preexisting or caused by fluctuation of stresses and temperature; they deteriorate in a runaway mode evolving towards effective linear or nonlinear shunts. Here we present a simplified analytical treatment and numerical modeling of such a nonuniform degradation tracking local deterioration and effects of weak spots on the integral cell parameters.