This Small Business Innovation Research (SBIR) Phase I project aims to use a new top-down Aluminum Induced Crystallization (TAIC) technology to create thin-film silicon solar modules with over 12% efficiency. First, large-grain crystallization of hydrogenated amorphous silicon thin film with thicknesses needed for solar cells will be obtained using TAIC. Second, the doping of resultant films to suitable levels by annealing samples in an atomic hydrogen environment will be studied. It is expected to create over 12% efficiency thin-film solar modules with low temperatures (less than 300 degree Celsius) required.
The broader/commercial impact of this project will be the potential to provide a method for thin-film silicon solar cell manufacturers to effectively improve the energy conversion efficiency with minimal additional cost. The limited efficiencies of amorphous silicon thin-film solar cells curtail their market adoption. While polycrystalline silicon solar cells have the highest potential of any thin-film silicon option, the manufacturability is still a concern. Current crystallization process requires temperatures in excess of 550 degree Celsius for over 20 hours. In this project, TAIC technology will be utilized to eliminate these disadvantages to manufacturing by creating very large-grain polycrystalline silicon thin films at low temperatures and in a short time (minutes).
Top-down aluminum induced crystallization (TAIC) of amorphous silicon into large-grain polycrystalline silicon is a versatile technology with applications in photovoltaics, power electronics, as well as display electronics. The main benefits of this method over other crystallization techniques include requiring the lowest crystallization temperatures, short annealing times, and producing very large grains. Solid phase crystallization, SPC, (simply annealing amorphous silicon) requires >600°C for more than 20 hours. Grain sizes resulting from SPC normally range from hundreds of nanometers to just a few microns. At this grain size range, the electronic properties of the polysilicon are limited by electrically active defects at the grain boundaries. For this reason, larger grain sizes are needed for device-ready materials. During this project we achieved grains in excess of what had been reported with even our own technology (up to 150µm). We also demonstrated the possibility of crystallization without layers of amorphous silicon and metal changing places and even doping the amorphous silicon without crystallization at very low temperatures. One application we are pursuing with this technology is to create seed layers for epitaxially grown solar cells in collaboration with researchers at the National Renewable Energy Laboratories (NREL) and at IMEC in Belgium. Work is ongoing in order to assess more advanced cell structures using only our technology to completely enable thin-film silicon photovoltaics. The work completed under this Phase I grant has resulted in additional private equity investment, increase in employment, and numerous supplementary grant applications.
