Distortion of Suns-V OC Measurements due to Plated Copper Diffusion through Silver Capping Layers on Silicon Solar Cells

This paper reports on the observed diffusion of plated copper through silver capping layers during thermal stability testing of copper-plated silicon solar cells. Distortion of Suns-V OC curves was observed on plated solar cells after extended thermal exposure at 200 °C for 500 hrs, reducing the accuracy of Arrhenius analyses of long-term stability. Cross-sectional imaging revealed the source of the distortion to be high contact resistance due to void formation between the bulk copper and the silver capping layer in the contact stack, the voids occurring as a result of copper diffusing through the capping metal. The extent of void formation was shown to be dependent on the microstructure of the capping layer, highlighting the limitations of using plated metals as diffusion barriers.