Evaluation of Nanoindentation Load-depth of Ultrasonic Aluminium Bond on Molybdenum Back Contact Layer of CIGS Thin Film Photovoltaic

This study evaluates the micromechanical properties of ultrasonic aluminium bonds on molybdenum back contact layers of Copper Indium Gallium Selenide (CIGS) thin film photovoltaic through nanoindentation testing. The analysis focuses on load-depth (P-h) profiles, pop-in events, hardness, and reduced modulus at different stages of high temperature storage (HTS) at 150 °C over 0, 400, and 800 hours. Results reveal that the aluminium bond subjected to 800 hours of HTS shows an increase in pop-in events, indicating enhanced plastic deformation, while prolonged HTS impacts hardness differently at the peak and valley regions of the bonds. This behaviour is attributed to grain refinement and increased dislocation density, which provide resistance to the indenter penetration, enhancing material hardness. Furthermore, changes in reduced modulus, particularly at 400 hours, indicate the crystallographic alignment of the aluminium bond. These findings contribute to understanding the mechanical durability and reliability of ultrasonic aluminium bonds for photovoltaic applications, supporting the development of more resilient interconnection strategies.