Keep it Simple: Low-Cost Solar Power

A simplified architecture leads to efficiencies rivaling conventional silicon solar cells.

The cross-section shows key features of a new solar cell architecture. — Image courtesy of Ali Javey of University of California, Berkeley

The Science

A new architecture takes very few processing steps to produce an affordable solar cell with efficiencies comparable to conventional silicon solar cells. This new architecture uses alternative, transparent materials that can be deposited at room temperature, eliminating the need for high temperature chemical doping—the process currently used to increase the electrical conductivity of key surfaces in solar cells.

The Impact

Proving that this simple design can lead to high conversion efficiencies, turning sunlight into electricity, makes it a useful tool to lower costs and improve performance of a wide range of solar cell designs. Additionally, this simple process could be extended to improve contacts in semiconductor transistors used to speed today’s computers.

Summary

In this simplified architecture, sunlight passes through the top layer (metal oxide) and creates electron-hole pairs in the silicon. The holes are drawn to the molybdenum oxide layer, while the electrons are drawn to the lithium fluoride layer, which can be used to produce electricity. This design uses a seven-step process and low-temperature processing to produce a device that efficiently separates photo-generated elections and holes. In this process, the crystalline silicon with a pyramid texture is coated with a passivating layer of amorphous silicon. Then, molybdenum oxide is deposited at room temperature on the top side of the device. Molybdenum oxide advantageously is transparent, allowing the sunlight to reach the silicon core, and has the appropriate electronic properties to conduct the photo-generated holes. Next, lithium fluoride is deposited at room temperature onto the bottom side of the solar cell to draw the photo-generated electrons from the silicon core. This simple, processing is less expensive than conventional processing for silicon solar cells that requires chemical doping at high temperatures to create contacts that separate the photo-generated electrons and holes. Impressively, the simplified architecture achieves solar energy conversion comparable to conventional silicon solar cells at a lower cost.

Contact

Ali Javey
University of California, Berkeley
Lawrence Berkeley National Laboratory
ajavey@eecs.berkeley.edu

Funding

This work was supported by the DOE Office of Science (Office of Basic Energy Sciences) (materials characterization); the Molecular Foundry, a DOE Office of Science User Facility; Bay Area Photovoltaics Consortium (device design, fabrication and characterization); Joint Center for Artificial Photosynthesis, a DOE Office of Science Energy Innovation Hub (XPS characterization); Office fedéral de l'énergie (Swiss Federal Institute of Technology of Lausanne); and Australian Renewable Energy Agency (Australian National University).

Publications

J. Bullock, M. Hettick, J. Geissbühler, A. J. Ong, T. Allen, C. M. Sutter-Fella, T. Chen, H. Ota, E. W. Schaler, S. De Wolf, C. Ballif, A. Cuevas, and A. Javey, "Efficient silicon solar cells with dopant-free asymmetric heterocontacts." Nature Energy 15031, 1 (2016). [DOI: 10.1038/nenergy.2015.31].