After settling a lawsuit (“SoloPower ends ex-CEO suit with $19.9M payment”) with Crosslink Capital, Hudson Clean Energy Partners, and other SoloPower investors in February 2010, former SoloPower, Inc. CEO Homayoun Talieh or Chief Technology Officer (CTO) Dr. Bulent Basol could just have said, I’m going to Disney World!
Instead, Bulent Basol founded and Homayoun Talieh co-founded EncoreSolar, Inc. towards the end of March 2010. Whether precluded by a non-compete agreement with SoloPower or tired of the complex phase diagram of the CIGS (copper indium gallium diselenide) material set, the EncoreSolar founders elected to return to their CdTe (Cadmium Telluride) PV technology roots researching and developing electroplating processes to produce low cost, high efficiency CdTe thin film modules. EncoreSolar’s goal is to be cost and efficiency competitive with crystalline silicon (c-Si) and CIGS thin film PV technologies.
In a company presentation, EncoreSolar highlights CdTe is easy to form especially versus CIGS, the ability to produce monolithic integrated CdTe modules with a single encapsulant layer, cost reduction potential to $0.50-0.70 per Watt, and high energy yield in kilowatt-hours per kilowatt (kW-h/kW).
EncoreSolar also cites the following Identified Needs in the June 2007 “National Solar Technology Roadmap: CdTe PV” report from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Program:
Improve Device Efficiency
Reduce absorber-layer thickness to 0.7 μm.
Develop and test promising materials, device designs, and process steps that are not a part of present module production.
EncoreSolar believes an electrodeposition process can reduce and control the thickness of the CdS (Cadmium Sulfide)/CdTe absorber layer and enable new device designs. After electrodeposition, common CdTe process steps include treating the CdS/CdTe, contact deposition, and packaging.
EncoreSolar claims the following advantages for electrodeposition versus physical vapor deposition (PVD) or printing of paste or nanoparticle ink:
Is low cost in terms of equipment, utilities usage (low temperature ~ 70-80 ̊C)
Does not require pure CdTe powder as the starting material
Has near-100% materials utilization
Can produce thin (0.7-2um) films for solar cell fabrication thus improving materials utilization further
Has the potential to offer higher efficiency solar cells through interface engineering/new device designs at low temperature
Can be scaled up for both RIGID and FLEXIBLE modules of large size (no temperature limitation due to glass softening)
High Efficiency Structures
On the potential of higher efficiency CdTe device structures, EncoreSolar was inspired by Colorado State University Department of Physics research directed by James R. Sites, Ph.D., and supported by Abound Solar, Inc. through the U.S. Department of Energy’s photovoltaic incubator program.
A paper presented at the 34th IEEE Photovoltaic Specialist Conference (PVSC 34):
Kuo-Jui Hsiao, James R. Sites, “Electron Reflector Strategy for CdTe Solar Cells”, Proc. 34st IEEE Photovoltaics Specialists Conf., Philadelphia (2009), pp. 001846- 001850.
is summarized by EncoreSolar as:
In this work, one-dimensional numerical simulation was used to evaluate the potential effect of electron and optical reflection on CdTe solar cells. For the optimal effect from an electron reflector, assuming no change in cell quality otherwise, the CdTe thickness should be on the order of 1 μm, or slightly lower if the optical reflection at the back surface can be enhanced. Based on the simulation, efficiency above 19% should be possible with a 0.2-eV electron reflector and currently achievable parameters (1014-cm-3 hole density and 1-ns lifetime). Moreover, 20% efficiency should be possible if large optical back reflection is also achievable.
EncoreSolar’s electrodeposition process is synergistic with optimizing CdTe thickness for the electron reflector. The subsequent full dissertation by Mr. Kuo-Jui Hsiao, Ph.D., can be downloaded here:
Kuo-Jui Hsiao, “Electron-reflector strategy for CdTe thin-film solar cells”, Ph.D. dissertation, Colorado State University, 2010.
The theoretical frame of the electron-reflector strategy has been built. The future work should focus on the quantitative experimental investigation. This work should in particular focus on:
1. Optimizing the fabrication process of a CdTe solar cell with an electron reflector.
2. Determining the electron-reflector barrier height.
3. Testing the simulation results.
No record CdTe cells have been reported for almost ten years, since the 16.5%-efficiency record cell was reported. Based on this dissertation, a major breakthrough in CdTe-solar-cell efficiency is possible with the electron-reflector strategy.
In June 2010, EncoreSolar moved into the old ASM NuTool building in Fremont, California USA. During the first few months, equipment was ordered and installed while the requisite permits were obtained, and the lab was operational by September. By the end of October 2010, “8.8% efficient solar cells were made” and appear to have been verified by the University of Delaware Institute of Energy Conversion. EncoreSolar has developed or is developing a large area electroplater capable of dry-in, dry-out processing (4) four substrates up to 2 x 6 feet (0.61 x 1.83 meter) in size.
Building on Dr. Basol’s development of fundamental CdTe fabrication technology at Monosolar in the early 1980’s, EncoreSolar had developed five (5) new inventions “geared towards processing and module efficiency improvements” as of late 2010.
EncoreSolar’s has not disclosed their investors or financing to date. Recent events point to self-funding by the founders and perhaps angel investors with participation by the Board of Directors or their affiliated companies also possible.
EncoreSolar did not acknowledge my questions or request for an interview.
I imagine First Solar is also hard at work researching higher efficiency CdTe device designs and enhancing and rethinking their fabrication processes.
(Full disclosure: I own some shares of FSLR stock.)