Ultra-Thin III-V Films for Tandem Photovoltaic Application

III-V semiconductors based solar cells display the highest sunlight conversion efficiency. Nevertheless, the material cost of current III-Vs and their fabrication process is very high which impedes their use for flat panel, large market applications. This project aims to explore, evaluate and implement defect tolerant high efficiency tandem solar cells based on more earth abundant III-V materials with low dimensionality substrates. In this Phase I project a device model of solar cells exhibiting high dislocation densities will be validated through the fabrication of (Al) GaAs p/n junction top cells with intentional high dislocation densities by Molecular Beam Epitaxy (MBE). Extracted material and device parameters will be used to refine the model. Such model can be extended to other emerging thin film materials. In a parallel effort, 1 to 1.2 eV GaAsSbP and GaAsSbN based bottom solar cells will be fabricated by MBE and will undergo routine structural and optoelectronic characterization in order to study their feasibility.Commercial Applications and Other Benefits: Much thinner device architectures than current III-V technology are expected to increase defect tolerance while substantially cutting manufacturing cost. In the subsequent phases of the project, a reel to reel deposition technique using low dimensionality substrates is envisioned in order to further cut costs while increasing production output. Cost effective, defect tolerant and high efficiency III-V thin film solar cells based on more earth abundant materials have a game changing potential in todays solar energy market. In particular, commercial applications such as the residential market will hugely benefit from the success of this project. Other benefits are job creations that directly benefit the economy and the possibility to combat global climate change as stated in the Presidents economic recovery package.