Current solar photovoltaic cells can be comparatively efficient but expensive, like those using single-crystal silicon, or inefficient and inexpensive, like those using thin film silicon. The compound semiconductors known as “III-V” are in the first group. This project aims to demonstrate a technology that could enable a dramatic change in the cost/performance tradeoff of photovoltaics. Rapid melt growth (RMG) uses inexpensive silicon wafers as substrates, but grows thin film III-V materials on these substrates using low-cost processes. The basic technology was developed at Stanford in the last decade, but for high performance computer applications. To utilize RMG technology for photovoltaic applications, two significant breakthroughs are required. First, the extension of the RMG method to full wafer coverage needs to be demonstrated. Second, low-cost structures for fully integrated solar cells using RMG materials need to be demonstrated.
This project is aimed at both of these objectives. We have made significant progress on the first technological challenge. We have explored experimentally the limits of the RMG method on areal coverage of thin film III-V materials, and have demonstrated methods to produce high areal coverage on inexpensive Si wafers. The second issue, demonstrating complete cell structures, is still under investigation, but we are confident that good solutions exist. Taken together, the large area coverage and viable cell structures could provide a game-changing solution to photovoltaic cell manufacturing. This remains our goal and we hope to complete a feasibility demonstration within the next six months.