Department of Energy, Office of 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.
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.
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.
This work was supported by the DOE Office of Science (Office of
Basic Energy Sciences) (materials characterization); 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).