Development of an Inverted GaAsP Photovoltaic Subcell Structure for Application to High-Efficiency III-V/Si Tandem Solar Cells

Solar power is a viable and sustainable energy source that does not harm the environment through pollution. Affordability of solar cells and other energy sources is measured in cost per power output (e.g. $/W). Thus, for a technology to serve as a primary energy source, it should have low production costs and sufficiently high-power output. One technology currently being developed as a solution for low-cost solar power is the III-V/Si multijunction solar cell. This device architecture combines the high efficiency of the III-V semiconductor with the low cost of Si technology to create a high-performance, cost-effective solar cell. Researchers at The Ohio State University have pioneered a GaAsP/Si tandem device. Initial results are promising, but the efficiency could still be improved. Given that Si solar cell technology is near its theoretical efficiency limit, the GaAsP cell has the greatest potential for optimization. The research described herein sought to optimize the efficiency of the GaAsP top cell for implementation in the GaAsP/Si multijunction structure by investigating different cell geometries, including a novel “inverted” design. Silvaco Technology Computer Aided Design (TCAD) software was first used to extract and identify key materials parameters from experimental data collected from a previously fabricated prototype device. This information was then used toward both the optimization of a conventional upright design and the development of a previously unexplored design. The two new resultant cell designs were then fabricated and characterized. The new upright design was found to yield a 2.5% absolute (or 20% relative) improvement in efficiency over the existing GaAsP cell and it was relatively-well-matched to the predicted results. However, the inverted cell design performed significantly worse than the existing GaAsP cell and did not match the predicted cell’s performance. Re-examination of the model and experimental results has revealed that a previously unknown electronic structure feature is present and significantly hindering device performance. This has led to more ongoing work to determine the viability of the inverted cell design.Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE)The Ohio State University Electronic Materials & Devices LaboratoryA five-year embargo was granted for this item.Academic Major: Electrical and Computer Engineerin