This Small Business Innovation Research (SBIR) Phase I project aims to develop a practical manufacturing process and the key enabling hardware for Emitter Wrap Through (EWT) solar cells. EWT technology is significant because it can improve the efficiency of crystalline-silicon solar cells to potentially above 20% energy conversion efficiency from the current 13-17% today. However, its promise has not been materialized because of the challenges in processing speed and cost. This project will utilize a recently developed high-power fiber laser technology based upon Arbor Photonics 3C optical fibers, along with fast beam scanning technology to enable the development of an economical and deployable process for EWT application. The expected outcome of this project is the development of a detailed baseline laser system that can achieve more than 10,000 holes per second in a cost-effective manner.
The broader/commercial impact of this project will be the potential to enable the wide adoption of EWT solar cells. The commercialization of EWT solar cells has not been realized due to the high manufacturing costs resulting from slow processing speeds that is currently less than 4,000 holes per second. The currently available commercial lasers cannot achieve the combination of pulse energy, duration and repetition rate to achieve the target of more than 10,000 holes per second required to make this process economically viable. A combination of recently developed high-power fiber laser technology from Arbor Photonics that extends the range of available operating laser parameters and fast beam scanning technology can enable development of an economical and deployable process for this application. The resulting process tool has the potential to address a portion of the $100 million market for laser-based tools used in Si solar cell manufacturing, a market segment that has seen year over year growth on the order of 60% per year in the last 5 years.
Arbor Photonics proposed to develop the key enabling hardware to enable a practical manufacturing process for making higher sunlight-to-electricity conversion efficiency (> 20%) crystalline-Silicon solar cells. Current commercial Silicon solar cells achieve sunlight to electricity conversion efficiency of only 10 to 20 percent. This limits the viability of solar energy as an alternative to fossil fuels. Emitter Wrap Through solar cells address this limitation by providing an architecture that increases conversion efficiency to > 20% while also allowing for the use of less expensive, multi-crystalline Silicon. The main barrier to bringing Emitter Wrap Through cells to market is that they require large numbers (>20,000) of holes through the wafer. The most promising technology for making through-holes is laser drilling, but available laser and scanning equipment has been unable to meet production fabrication rates of 1 wafer per second cost-effectively. As a result of the Phase I effort, an economical design for a laser with a beam delivery and scanning system for manufacturing high efficiency Emitter Wrap Through solar cells at target production speeds was developed. The laser/scanner system design was driven by top level process goals provided by a leading supplier of solar cell manufacturing equipment. In order to translate the process requirements to hardware requirements, the physics of the drilling process was studied, and an appropriate model for the laser drilling process was identified and calibrated against published empirical results and actual customer supplied process R&D data. The resulting system design, in its baseline configuration, is targeted to achieve a hole fabrication rate of at least 25,000 holes/sec, a 2.7X increase over the current state-of-the-art, and is scalable to fabrication rates of 50,000 holes/sec and beyond. The innovative system incorporates fiber optic technology, recently developed by Arbor Photonics, that permits a significant increase in available pulse energy from single-mode fiber lasers. The pulsed fiber laser enables additional power/energy scaling via spectral combining and features maximum flexibility for laser parameter optimization due to the master oscillator power amplifier laser design. It also incorporates a new concept that decouples the relationship between scan speed and pulse width to allow longer pulse widths to be used at high scan speeds, dramatically reducing the cost and complexity of laser systems for high speed hole fabrication. Energy diversification beyond fossil fuel sources is an area of intense national attention. While there remain challenges to bringing solar cell solutions to cost parity with current non-renewable energy sources, parity has been reached with specific solar installations. To continue this trend, it is necessary to improve efficiency of solar cells using cost-effective manufacturing processes. Because crystalline-Silicon solar cells make up the bulk of solar cells on the market today (>70%), additional cost reduction in these cells can have the biggest impact on widespread adoption of solar energy. Improving solar cell efficiency without substantial increases in manufacturing costs is a key pathway to further reductions in solar energy cost. One promising innovation is the Emitter Wrap Through (EWT) cell architecture, which has been demonstrated with up to 21.4% efficiency. Despite these considerable advantages, EWT cells have not yet been commercialized. Through Arbor Photonics’ Phase I project, the necessary hardware for a manufacturing process for higher efficiency Crystalline Silicon solar cells was designed as a means to make a positive impact on renewable energy. Commercialization of this technology and product concept will provide a basis for U.S. based manufacturing leadership in this vitally important area of renewable energy technology.
