An exponential growth of photovoltaic (PV) technologies in the past decade has paved a path to a sustainable solarpowered world. The development of alternative PV technologies with low-cost and high-stability materials has attracted a growing amount of attention. One of these alternatives is the use of second generation thin film PV technologies. However, even in the presence of their bandgap properties, a major issue faced by most thin film solar cells is the low output efficiency due to manufacturing variability and uncertain operating conditions. Thus, to ensure the reliability and performance robustness of the thin film PV technologies, the design of the solar cell is studied. To represent the thin film PV technologies, a copper gallium (di)selenide (CIGS) solar cell model is developed and optimized with Reliability-based Robust Design Optimization (RBRDO) method. This model takes into account the variability of the structure and the material properties of the CIGS solar cells, and assumes an ideal-weather operating condition. This study presents a general methodology to optimize the design of the CIGS PV technologies and could be used to facilitate the development and assessment of new PV technologies with more robust performance in efficiency and stability.