Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Atomic switcheroo explains origins of thin-film solar cell mystery


Treating cadmium-telluride (CdTe) solar cell materials with cadmium-chloride improves their efficiency, but researchers have not fully understood why.

Now, an atomic-scale examination of the thin-film solar cells led by the Department of Energy’s Oak Ridge National Laboratory has answered this decades-long debate about the materials’ photovoltaic efficiency increase after treatment.

Cross-sectional electron beam-induced current maps show the difference in cadmium telluride solar cells before (pictured above) and after (below) cadmium chloride treatment. The increased brightness after treatment indicates higher current collection at the grain boundaries.

A research team from ORNL, the University of Toledo and DOE’s National Renewable Energy Laboratory used electron microscopy and computational simulations to explore the physical origins of the unexplained treatment process. The results are published in Physical Review Letters (PRL).

Thin-film CdTe solar cells are considered a potential rival to silicon-based photovoltaic systems because of their theoretically low cost per power output and ease of fabrication. Their comparatively low historical efficiency in converting sunlight into energy, however, has limited the technology’s widespread use, especially for home systems.

Research in the 1980s showed that treating CdTe thin films with cadmium-chloride significantly raises the cell’s efficiency, but scientists have been unable to determine the underlying causes. ORNL’s Chen Li, first author on the PRL study, explains that the answer lay in investigating the material at an atomic level.

“We knew that chlorine was responsible for this magical effect, but we needed to find out where it went in the material’s structure,” Li said. “Only by understanding the structure can we understand what’s wrong in this solar cell -- why the efficiency is not high enough, and how can we push it further.”

By comparing the solar cells before and after chlorine treatment, the researchers realized that atom-scale grain boundaries were implicated in the enhanced performance. Grain boundaries are tiny defects that that normally act as roadblocks to efficiency, because they inhibit carrier collection which greatly reduces the solar cell power.

Using state of the art electron microscopy techniques to study the thin films’ structure and chemical composition after treatment, the researchers found that chlorine atoms replaced tellurium atoms within the grain boundaries. This atomic substitution creates local electric fields at the grain boundaries that boost the material’s photovoltaic performance instead of damaging it.

The research team’s finding, in addition to providing a long-awaited explanation, could be used to guide engineering of higher-efficiency CdTe solar cells. Controlling the grain boundary structure, says Li, is a new direction that could help raise the cell efficiencies closer to the theoretical maximum of 32 percent light-to-energy conversion. Currently, the record CdTe cell efficiency is only 20.4 percent.

“We think that if all the grain boundaries in a thin film material could be aligned in same direction, it could improve cell efficiency even further,” Li said.

The team’s research appears as “Grain-Boundary-Enhanced Carrier Collection in CdTe Solar Cells.” Coauthors are ORNL’s Chen Li, Jonathan Poplawsky, Mark Oxley and Andrew Lupini; University of Toledo’s Yelong Wu, Naba Paudel, Wanjian Yin and Yanfa Yan; University of Tennessee’s Stephen Pennycook; University of Manchester’s Sarah Haigh; University of Oxford’s Timothy Pennycook; and NREL’s Mowafak Al-Jassim. Li and Oxley hold joint appointments at Vanderbilt University.

The research was supported by the Department of Energy’s Office of Energy Efficiency and Renewable Energy through the SunShot Initiative and the Office of Basic Energy Sciences. The work was sponsored in part by the UK Engineering and Physical Sciences Research Council and through a user project supported by ORNL’s Center for Nanophase Materials Sciences (CNMS). This research used resources of the National Energy Research Scientific Computing Center. Yan acknowledges support from the Ohio Research Scholar Program.

CNMS is one of the five DOE Nanoscale Science Research Centers, NSRCs, supported by the DOE Office of Science, as premier national user facilities for interdisciplinary research at the nanoscale. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE's Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos national laboratories.  For more information about the DOE NSRCs, please visit

ORNL is managed by UT-Battelle for the Department of Energy's Office of Science.

DOE’s 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

Morgan McCorkle | Eurek Alert!
Further information:

Further reports about: Atomic CdTe Computing Energy ORNL energy nanoscale responsible tellurium

More articles from Power and Electrical Engineering:

nachricht New method increases energy density in lithium batteries
24.10.2016 | Columbia University School of Engineering and Applied Science

nachricht 'Super yeast' has the power to improve economics of biofuels
18.10.2016 | University of Wisconsin-Madison

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: New 3-D wiring technique brings scalable quantum computers closer to reality

Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.

"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...

Im Focus: Scientists develop a semiconductor nanocomposite material that moves in response to light

In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.

A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...

Im Focus: Diamonds aren't forever: Sandia, Harvard team create first quantum computer bridge

By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.

"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...

Im Focus: New Products - Highlights of COMPAMED 2016

COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.

In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...

Im Focus: Ultra-thin ferroelectric material for next-generation electronics

'Ferroelectric' materials can switch between different states of electrical polarization in response to an external electric field. This flexibility means they show promise for many applications, for example in electronic devices and computer memory. Current ferroelectric materials are highly valued for their thermal and chemical stability and rapid electro-mechanical responses, but creating a material that is scalable down to the tiny sizes needed for technologies like silicon-based semiconductors (Si-based CMOS) has proven challenging.

Now, Hiroshi Funakubo and co-workers at the Tokyo Institute of Technology, in collaboration with researchers across Japan, have conducted experiments to...

All Focus news of the innovation-report >>>



Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

Agricultural Trade Developments and Potentials in Central Asia and the South Caucasus

14.10.2016 | Event News

World Health Summit – Day Three: A Call to Action

12.10.2016 | Event News

Latest News

New method increases energy density in lithium batteries

24.10.2016 | Power and Electrical Engineering

International team discovers novel Alzheimer's disease risk gene among Icelanders

24.10.2016 | Life Sciences

New bacteria groups, and stunning diversity, discovered underground

24.10.2016 | Life Sciences

More VideoLinks >>>