This Small Business Innovation Research (SBIR) Phase I project aims to develop a solution-based technique to deposit doped zinc oxide thin film with resistivity that is 1 x 10-4 Ohm-cm or lower. An abundant and low-cost material will be used as the dopant. Structural and optical properties, and effects of post-deposition annealing will be studied to improve the conductivity of doped zinc oxide thin films. With further efforts beyond this project to continuously improve the conductivity, the doped zinc oxide thin film is expected to be used as transparent conductive oxide (TCO) in thin-film solar cells.
The broader/commercial impact of this project will be the potential to provide a viable material candidate as a low-cost alternative to the commonly used TCO in thin-film solar cells. Currently, TCOs are generally deposited by vacuum-based sputtering process, which is not as cost-effective as solution-based technique. With the expected fast growth of thin-film solar cells in the coming decades, the availability of low-cost TCO will be critical to reduce the overall cost of thin-film solar cell, thus making it more affordable.
Principal Investigator: Lilly Q. Guo Tao Companies LLC This Small Business Innovation Research Phase I project develops a low-cost deposition method for a new transparent conducting oxide. The deposition method is solution based and the new transparent conducting oxide is yttrium-doped zinc oxide. Transparent conducting oxide is an indispensible component in all thin-film and next-generation solar cells. However, all the current transparent conducting oxides suffer from one or another problem which hinders their large-scale applications in solar cells. The goal of this project is to develop a new transparent conducting oxide which does not suffer from any of the problems other transparent conducting oxides suffer. In this regard, a spray deposition process has been developed for yttrium-doped zinc oxide. Many of the deposition parameters and post-annealing parameters have been optimized to achieve the best performance possible. The lowest resistivity we have achieved so far, the most important performance parameter for transparent conducting oxides, is 7×10-3 Ohm-cm. Our spray-deposited yttrium-doped zinc oxide removes several major roadblocks for zinc oxide to become an industry-standard low-cost high-performance transparent conducting oxide in terawatt-scale solar cells: 1) cost, since solution-based deposition is inherently lower cost; 2) performance, since yttrium-doped zinc oxide compares favorably to the best transparent conducting oxide in performance; and 3) material abundance, since yttrium-doped zinc oxide uses abundant source materials with enough reserves for tens of terawatts of solar cells. Our spray-deposited yttrium-doped zinc oxide is a candidate to replace commercial fluorine-doped tin oxide with better performance. In 2009, thin-film solar cells accounted for ~$4B in annual sales. If solar cells are to be a noticeable source of energy in our society, the solar cell industry has to expand more than 1,000-fold in the next few decades. With the exponential growth expected for thin-film solar cells in the coming decades, the impact of this technology will become much more significant.
