Long-term stability of amorphous silicon solar cells and modules☆

Abstract Thermal stability of Ala-Si:H and AlSnO 2 interfaces and the photostability of the a-Si:H (hydrogenated amorphous silicon) are the two major factors controlling the long-term stability of a-Si solar cells and molules. Recent advances made in understanding and in some cases in solving these problems are discussed in the present paper. The rapid diffusion of silicon through the grain boundaries of the aluminum film was found to be the primary mechanism responsible for the instability of the Ala-Si:H interface. The degradation of the AlSnO 2 contact is the result of the reduction of SnO 2 by the aluminum, causing the formation of an insulating Al 2 O 3 interface layer. Results from a special aluminum metallization technique that substantially improves the stability of these two interfaces will be presented. Experimental results on the kinetics of the photodegradation and thermal recovery of the photoconductivity in a-Si:H films will be reported. Accelerated light soaking tests on various a-Si modules will also be reported. In this context, several examples of the inverse Staebler-Wronski effect, where the efficiency of the solar cell initially increases with light soaking time, will be provided.