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Field-effect P-N Junctions for Low Cost, High Efficiency Solar Cells and Electronic Devices

IB-3094

Self-powered Gating and Other Improvements for Screening-engineered Field-effect Photovoltaics

IB-3170

APPLICATIONS OF TECHNOLOGY:

ADVANTAGES:

ABSTRACT:

IB-3094

Berkeley Lab scientists Alex Zettl and William Regan have developed a straightforward technology that enables fabrication of high efficiency, single junction photovoltaic (PV) cells from inexpensive, abundant, and nontoxic materials—notably metal oxides and sulfides. Berkeley Lab’s field-effect p-n junction lowers manufacturing costs and increases the efficiencies of PV cells and other electronic devices without the need for costly chemical doping techniques. In addition to solar cells, this technology can be used to produce LEDs and laser diodes from a variety of abundant, nontoxic semiconducting materials which emit at currently inaccessible wavelengths, providing new commercial opportunities in lighting systems, optical storage, and medical applications.

The technology adapts the well-known field-effect—in which a gate controls band bending in a nearby semiconductor—to produce electrically contacted p-n junctions in intrinsically singly doped semiconductors. Using a sophisticated theoretical model tailored to semiconductors of choice, the gate and top electrode configuration is systematically optimized to allow simultaneous electrical contact to and carrier modulation of the top surface of the semiconductor. This field-effect “doping” is a compelling alternative to chemical doping or intrinsic heterojunction formation. The process requires only electrode and gate deposition, without high-temperature chemical doping, ion implantation, or other processing.

Compared to existing p-n junction fabrication methods, the Berkeley Lab technology reduces the cost and complexity of fabricating devices such as solar cells and LEDs; results in higher quality p-n junctions; and allows the creation of p-n junctions in abundant, nontoxic materials that are difficult or impossible to dope by conventional methods. Such materials include metal sulfide and oxide semiconductors such as cuprous oxide, which has a theoretical photovoltaic efficiency greater than 20%. In addition, established photovoltaics and electronics manufacturers using toxic or rare materials could quickly adapt this simple technology to current production processes, easing the transition to incorporating sustainable and inexpensive materials in their devices.

Photovoltaics are a promising source of renewable energy, but current technologies, including thin films, face a cost-to-efficiency tradeoff that has slowed their implementation. Chemically doped crystalline silicon is fast approaching fundamental cost minima. Competing thin film technologies depend on hazardous materials such as cadmium, or increasingly rare materials, such as indium (for copper-indium-gallide-selenide PV cells).

IB-3170

The Berkeley Lab scientists further improved on IB-3094 by creating several methods for powering the gate field in the innovative p-n junction to eliminate the need for any external power sources. In one method, the gate electric field is maintained by a “self-gating” feedback loop in which a wire connects the cell output to the gate contact. An alternate method to power the gate utilizes materials with fixed surface or bulk charge, including many dielectrics (e.g., alumina), ferroelectrics, and electrolytes. Various configurations combining these two new techniques have been developed that boost the gating effect, which improves the cell performance even further.  Strategies have been developed for both vertical and back-contact-only devices.

Zettl and Regan have also added a new architecture to their class of field-effect cells, especially suitable for thin film photovoltaics, in which screening is minimized.  Strategies are proposed for self-gating this new architecture.

DEVELOPMENT STAGE: Proven principle.

STATUS: Patent pending. Available for licensing or collaborative research.

FOR MORE INFORMATION:

http://newscenter.lbl.gov/feature-stories/2012/07/26/photovoltaics-from-any-semiconductor/

Regan, W., Byrnes, S., Gannett, W., Ergen, O., Vazquez-Mena, O., Wang, F., and Zettl, A. "Screening-Engineered Field-Effect Solar Cells," Nano Letters, Vol. 12, pp. 4300−4304, 2012.

REFERENCE NUMBER: IB-3094, IB-3170

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Last updated: 09/06/2012