Effect of oxide diffusion barrier and substrate on the reliability of stainless-steel-based CIGS solar cells

Abstract

This paper investigates the effect of the oxide diffusion barrier and substrate on the residual stress and the delamination at the CIGS/Molybdenum (Mo) interface when stainless-steel-based CIGS solar cells cool down to room temperature from the CIGS deposition process (500 °C) and hotspot conditions (100, 200, 300, and 400 °C). The focus is on the performance of Al2O3 and SiO2 oxide diffusion barriers and SS 304, SS Duplex, and SS 430 substrates. Through Finite Element method (FEM) and Machine Learning (ML) simulations, we calculated the energy release rate (J integral) of the CIGS/Mo interface crack and residual stress of the CIGS layer while concurrently varying the thickness of the diffusion barrier layer from 0.1 to 3 μm and the SS substrate from 25 to 200 μm. ML algorithms were used to predict the J integral at the CIGS/Mo interface and the CIGS residual stress for arbitrary CIGS deposition temperatures. Our simulation method is validated by the agreement between some of our simulation results and experimental findings from other researchers. Based on the simulation results, the following key findings were observed 1) A thinner diffusion barrier (for both SiO2 and Al2O3) is more effective in preventing the delamination at the CIGS/Mo interface, but a thicker diffusion barrier is more effective in reducing the stress in the CIGS layer 2) SiO2 diffusion barrier is better suited for preventing the CIGS/Mo interface delamination, while an Al2O3 diffusion barrier is better suited for reducing the residual stress in the CIGS layer 3) The thickness of stainless steel substrate significantly alters the residual stress in the CIGS layer (up to ∼30 times) 4) The SS 430 substrate is better suited for minimizing the residual stress in the CIGS layer and preventing delamination at the CIGS/Mo interface. The proposed methodology can be applied to other flexible solar cells to enhance their reliability.