Solar cells convert solar irradiance directly into electricity. The stability of the solar cell modules over time is important in addressing the problem of sustainability. Alternative materials and technologies have been proposed over the years for low cost and efficient solar cells. Fabrication of solar cells involves deposition of several thin film layers on top of each other. This book reports results of experiments on the formation of hetero-junction interfaces based of the concept of nanocomposite solar cells. The role of thin film deposition parameters, atomic inter-diffusion and impurities for band alignment and electronic charge transfer across the nanocomposite hetero-interfaces is reported. The results are related to current-voltage characteristics of extremely thin absorber solar cells and recommendations are made on how they can be improved. This work provides important information and additional knowledge for materials scientists, physicists and chemists that will contribute towards improved photovoltaic energy conversion.