This Small Business Innovation Research Phase I project aims to develop a nanopackaging process that can assemble high efficiency solar cells onto flexible panels. This modular, scalable approach leverages disparate, state-of-the-art photovoltaic technologies and integrates them into a single system at low temperature. This can include silicon, gallium arsenide and other III-V technologies. An advantage of the proposed approach is that it facilitates the use of silicon cells with III-V cells, increasing the availability of photovoltaic materials with different bandgaps. The assembled device will be evaluated for both concentrator applications and also portable electronic devices.
The broader impact/commercial potential of this project includes reducing dependence on fossil fuels, as well as limiting environmental impact compared to other sources of energy. Solar power is a renewable and nearly limitless energy source. Commercially, the project reduces manufacturing costs of flexible solar panels and introduces a more robust solar energy system into the market. The market for flexible solar panel substrates is estimated to be $536 million by 2017. Higher efficiency is critical for applications that utilize solar energy to extend the operational duration of mobile devices. However, the efficiency of commercially available flexible solar panels is limited to 8-14%. The challenge is that high temperature deposition processes are typically required to deposit higher efficiency materials, but the deposition temperature must be kept low for compatibility with flexible organic substrates. Key applications include concentrators and portable electronic devices.
In the NSF STTR Phase I project, the Blue Sky Engineering team sought to develop high efficiency multijunction solar cells for concentrating photovoltaic (CPV) systems. By combining photovoltaic layers for different wavelengths, the efficiency of the proposed solar cells can theoretically exceed 50%. Compared to competing approaches, microassembly techniques may offer a low-cost batch process for high efficiency solar cells. Furthermore, assembly approaches circumvent traditional lattice match and current requirements for typical monolithic approaches. The Blue Sky Engineering team successfully met the Phase I project objective to assemble III-V photovoltaic layers. The project developed process technologies for working with III-V materials such as gallium arsenide and aluminum gallium arsenide, which leveraged well-known chemistries developed for epitaxial liftoff approaches. This included working out different wet etches for III-V material systems such as those based on hydrofluoric acid. Furthermore, equipment optimization was performed to reduce the stresses that would be applied to the fragile III-V microstructures during the fabrication process. The process technologies and equipment capabilities have provided a proof-of-concept for low-cost multijunction microstructures. Potential follow-on work may focus on fabrication yield, further stress reduction during bonding and solar cell performance optimization. The technology development effort was guided by feedback from CPV manufacturers and the Department of Energy / National Renewable Energy Laboratory.
