Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Simplifying solar cells with a new mix of materials

28.01.2016

Berkeley Lab-led research team creates a high-efficiency device in 7 steps

An international research team has simplified the steps to create highly efficient silicon solar cells by applying a new mix of materials to a standard design. Arrays of solar cells are used in solar panels to convert sunlight to electricity.


In this illustration, the top images show a cross-section of a solar cell design, called DASH, that uses a combination of moly oxide and lithium fluoride. This combination of materials allows the device to achieve high efficiency in converting sunlight to energy without the need for a process known as doping. The bottom images shows the dimensions of the DASH solar cell components.

Credit: (Nature Energy: 10.1038/nenergy.2015.31)

The special blend of materials--which could also prove useful in semiconductor components--eliminates the need for a process known as doping that steers the device's properties by introducing foreign atoms to its electrical contacts. This doping process adds complexity to the device and can degrade its performance.

"The solar cell industry is driven by the need to reduce costs and increase performance," said James Bullock, the lead author of the study, published this week in Nature Energy. Bullock participated in the study as a visiting researcher at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley.

"If you look at the architecture of the solar cell we made, it is very simple," said Bullock, of Australian National University (ANU). "That simplicity can translate to reduced cost."

Other scientists from Berkeley Lab, UC Berkeley, ANU and The Swiss Federal Institute of Technology of Lausanne (EPFL) also participated in the study.

Bullock added, "Conventional silicon solar cells use a process called impurity doping, which does bring about a number of limitations that are making further progress increasingly difficult."

Most of today's solar cells use crystalline silicon wafers. The wafer itself, and sometimes the layers deposited on the wafer, are doped with atoms that either have electrons to spare when they bond with silicon atoms, or alternatively generate electron deficiencies, or "holes." In both cases, this doping enhances electrical conductivity.

In these devices, two types of dopant atoms are required at the solar cell's electrical contacts to regulate how the electrons and holes travel in a solar cell so that sunlight is efficiently converted to electrical current that flows out of the cell.

Crystalline silicon-based solar cells with doped contacts can exceed 20 percent efficiency--meaning more than 20 percent of the sun's energy is converted to electricity. A dopant-free silicon cell had not previously exceeded 14 percent efficiency.

The new study, though, demonstrated a dopant-free silicon cell, referred to as a DASH cell (dopant free asymmetric heterocontact), with an average efficiency above 19 percent. This increased efficiency is a product of the new materials and a simple coating process for layers on the top and bottom of the device. Researchers showed it's possible to create their solar cell in just seven steps.

In this study, the research team used a crystalline silicon core (or wafer) and applied layers of dopant-free type of silicon called amorphous silicon.

Then, they applied ultrathin coatings of a material called molybdenum oxide, also known as moly oxide, at the sun-facing side of the solar cell, and lithium fluoride at the bottom surface. The two layers, having thicknesses of tens of nanometers, act as dopant-free contacts for holes and electrons, respectively.

"Moly oxide and lithium fluoride have properties that make them ideal for dopant-free electrical contacts," said Ali Javey, program leader of Electronic Materials at Berkeley Lab and a professor of Electrical Engineering and Computer Sciences at UC Berkeley.

Both materials are transparent, and they have complementary electronic structures that are well-suited for solar cells.

"They were previously explored for other types of devices, but they were not carefully explored by the crystalline silicon solar cell community," said Javey, the lead senior author of the study.

Javey noted that his group had discovered the utility of moly oxide as an efficient hole contact for crystalline silicon solar cells a couple of years ago. "It has a lot of defects, and these defects are critical and important for the arising properties. These are good defects," he said.

Stefaan de Wolf, another author who is team leader for crystalline silicon research at EPFL in Neuchâtel, Switzerland, said, "We have adapted the technology in our solar cell manufacturing platform at EPFL and found out that these moly oxide layers work extremely well when optimized and used in combination with thin amorphous layer of silicon on crystalline wafers. They allow amazing variations of our standard approach."

In the study, the team identified lithium fluoride as a good candidate for electron contacts to crystalline silicon coated with a thin amorphous layer. That layer complements the moly oxide layer for hole contacts.

The team used a room-temperature technique called thermal evaporation to deposit the layers of lithium fluoride and moly oxide for the new solar cell. There are many other materials that the research teams hopes to test to see if they can improve the cell's efficiency.

Javey said there is also promise for adapting the material mix used in the solar cell study to improve the performance of semiconductor transistors. "There's a critical need to reduce the contact resistance in transistors so we're trying to see if this can help."

###

Some off the work in this study was performed at The Molecular Foundry, a DOE Office of Science User Facility at Berkeley Lab.

This work was supported by the DOE Office of Science, Bay Area Photovoltaics Consortium (BAPVC); the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub; Office fédéral de l'énergie (OFEN); the Australian Renewable Energy Agency (ARENA) and the CSEM PV-center.

More information about Ali Javey's research is available here: http://nano.eecs.berkeley.edu/.

Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit http://www.lbl.gov.

The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Media Contact

Glenn Roberts Jr.
geroberts@lbl.gov
510-486-5582

 @BerkeleyLab

http://www.lbl.gov 

Glenn Roberts Jr. | EurekAlert!

More articles from Power and Electrical Engineering:

nachricht TU Graz researchers show that enzyme function inhibits battery ageing
21.03.2017 | Technische Universität Graz

nachricht New nanofiber marks important step in next generation battery development
13.03.2017 | Georgia Institute of Technology

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

Im Focus: Researchers Imitate Molecular Crowding in Cells

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.

Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Vanishing capillaries

23.03.2017 | Health and Medicine

Nanomagnetism in X-ray Light

23.03.2017 | Physics and Astronomy

Pulverizing electronic waste is green, clean -- and cold

22.03.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>