The proposed research will strengthen the CdTe PV innovation ecosystem. CdTe PV is now economically viable in many applications and suitable for gigawattscale implementation. The project will utilize CSU's state-of-the-art deposition system to pursue two separate routes to higher-efficiency manufacturing-friendly cells: (1) higher voltage from a new device structure that employs a Cd1-xMgxTe electron-reflector layer to reduce electron recombination, and (2) higher current with a larger band-gap CdS layer achieved by the incorporation of plasma activated oxygen species. The project will develop novel semiconductor alloys, novel processing methods, novel defect-passivation approaches, and novel device structures. At the same time, detailed understanding of the defects, interfaces, and the device physics of the advanced devices will be developed.
The most significant broader impact is the production of clean energy globally on an unprecedented scale. This will provide a major benefit for the U.S. economy and will create thousands of well-paying jobs in the U.S. It builds on the success of the CdTe PV industry, which now has the lowest cost-structure and largest production of any U.S. PV technology. . It also builds on the technology-transfer experience of the PI, co-founder of Abound Solar which has grown to 370 employees with current manufacturing at 65 MW/Yr and a near term target of 200 MW/Yr. This project will also provide well-trained students for the photovoltaic industry, which is growing rapidly and requires a highly skilled workforce. The PV-training approach at CSU is strongly team based: students from different disciplines work closely with each other, with engineers from industry, and in many cases with students at other universities.
Accelerating Innovation Research Next-Generation CdTe Photovoltaic Technology Project Outcome Energy sustainability is one of the great challenges facing humanity. Electricity generation by CdTe thin-film solar photovoltaics (PV) offers a strong potential to address this challenge. This is because the cost of electricity from CdTe PV is currently competitive with electricity from the grid in many parts of the world (6 cents/kWhr. from utility scale installations) [Greentech 2013] and the costs are decreasing at 7% per year. An example of such a utility scale installation is shown in the attached figure. The goal of this project was to increase the efficiency of CdTe PV and further reduce the cost of electricity. Intellectual Merit. The work performed under this project can help reduce the cost of solar generated electricity. With partial support from this project, new device structures for group II-VI cells were developed which enable a significant increase in performance. Additionally, these advances were demonstrated with processes and materials suitable for large scale manufacturing. The efficiency of CdTe PV device was increased from 10.6% to 16.4% on low cost sodalime glass with process suitable for mass production. These are some of the highest efficiencies that have been reported on these substrates. It is estimated that the efficiencies would be 18.3% on more transparent glass substrates. In this project, two successful alternatives to the CdS window layer were developed to increase the current. These are: (i) high resistance transparent (HRT) layer and CdS:O and (ii) ZnMgO. It was discovered that an optimum work function of the layer in contact with CdTe was needed to maintain good voltage. A bilayer of CdMgTe/Te at the back of CdTe increased the voltage of devices with thin CdTe. A technology for the rapid deposition of complex alloys such as CdMgTe over large areas was developed and patented. These are significant developments in the field of CdTe PV. Buffer layers have been investigated and used in CdTe PV . Work performed with partial support of this project provided one of the first solid scientific understanding of how theses materials enable increased device performance [ Kephart, 2015]. Broader Impacts. The most significant broader impact is the contribution to CdTe PV for the production of clean energy globally on an unprecedented scale. Some of the technologies were implemented in production lines. The PI’s group is actively working with the PV industry to transfer technologies developed including active engagement with the industry leading manufacturer, First Solar (Nasdaq: FSLR). All the results have been broadly disseminated in invited talks, publications, etc. The project has partially supported the graduate education of 6 Ph.D students, 2 M.S students and 14 undergraduate students. The PV-training approach at CSU is strongly team based: students from different disciplines work closely with each other, with engineers from industry, and in many cases with students at other universities. References: Greentech,www.greentechmedia.com/articles/read/first-solar-macho-update,accessed 2013. Kephart, Jason: Ph. D Dissertation, Optimization of the Front Contact to Minimize Short Circuit Current Losses in CdTe Thin Film Solar Cells, 2015.
