This Small Business Innovation Research (SBIR) Phase I project aims to develop a low-cost and high-efficiency multi-junction solar technology. Currently, most of low-cost thin-film solar technologies remain at efficiencies that are too low for the residential market, whereas high-efficiency multi-junction technology is generally a niche product for concentrators and space applications due to the high cost. In this project, a two-junction tandem cell will be developed by the combination of stable and efficient multi-crystalline Si as the low-gap junction and thin films with desired properties as the high-gap cell. The integrated tandem panels are anticipated to achieve 20% energy conversion efficiency. <br/><br/>The broader/commercial impact of this project will be the potential to provide a solar cell structure that is both cost-effective and highly-efficient. Renewable solar energy from photovoltaics is one of the best solutions to meet future energy demands. This project particularly targets on the residential sector of solar industry. Low cost, high efficiency and stability that this technology may offer are essential for the adoption of solar technology in this market.