PRESS-NEWS.org - Press Release Distribution
FREE PRESS RELEASES DISTRIBUTION

Plastic solar cells' new design promises bright future

Unprecedented fill factors of 80 percent come close to that of silicon solar cells

2013-08-14
(Press-News.org) Energy consumption is growing rapidly in the 21st century, with rising energy costs and sustainability issues greatly impacting the quality of human life. Harvesting energy directly from sunlight to generate electricity using photovoltaic technologies is considered to be one of the most promising opportunities to produce electricity in an environmentally benign fashion.

Among the various photovoltaic technologies, polymer (plastic) solar cells offer unique attractions and opportunities. These solar cells contain Earth-abundant and environmentally benign materials, can be made flexible and lightweight, and can be fabricated using roll-to-roll technologies similar to how newspapers are printed. But the challenge has been improving the cells' power-conversion efficiency.

Now a research team of faculty members and students led by Professor Tobin J. Marks of Northwestern University reports the design and synthesis of new polymer semiconductors and reports the realization of polymer solar cells with fill factors of 80 percent -- a first. This number is close to that of silicon solar cells.

"Our results indicate that the power-conversion efficiency achievable with polymer solar cells may be far beyond the current levels, heralding a bright future for this technology," Marks said. "With our high fill factors, polymers with very good but not champion light absorption still are able to achieve very good efficiency."

Marks is the Vladimir N. Ipatieff Research Professor of Chemistry in the Weinberg College of Arts and Sciences and Professor of Materials Science and Engineering in the McCormick School of Engineering and Applied Science.

The study was published Aug. 11 by the journal Nature Photonics.

The team showed that the exceptional fill factors arise from high levels of order in the mixture of polymer donor chains and buckyball acceptor components, the way these two components are distributed within the cell active layer, and a "face-on" orientation of the polymer chains on the electrode surface.

The fill factor achieved is more than 10 percent greater than previously achieved by the polymer solar cell community, and, in the present study, although the polymer semiconductors have non-optimal light absorption characteristics, a near-record power-conversion efficiency as high as 8.7 percent is still obtained.

The working principle of polymer solar cells differs greatly from that of traditional silicon solar cells. The active layers of polymer solar cells typically contain a mixture of polymer chains that can donate electrons and "buckyball" molecules that accept electrons. (Buckminsterfullerene, or buckyball, is a spherical fullerene molecule with the formula C60.)

Under solar irradiation, electronic excitation generates mobile electron-hole pairs called excitons. The excitons then diffuse through the active layer of the cell, separating at donor-acceptor interfaces into free charge carriers (electrons and holes) that are collected as electrical current when they reach the cell electrodes.

In spite of the attractions of polymer solar cells, their large-scale application has been limited by the relatively low power-conversion efficiency, which is defined as the percentage of the power generated by the cell versus the power of the incident sunlight. The power produced by a solar cell is the product of three cell performance parameters: the open circuit voltage, the short circuit current and the fill factor. Various strategies now are being developed to increase these parameters to maximize the power-conversion efficiency of the cells.

While there are reliable approaches to increase the cell's open circuit voltage and short circuit current, the realization of high fill factors has proven elusive, with fill factors of most polymer solar cells typically well below 70 percent, versus 80 percent for conventional silicon solar cells.

In polymer solar cells, achieving high fill factors is largely prevented by the recombination (self-annihilation) of the photogenerated electron-hole pairs before they reach the cell electrodes to be collected as current. In typical polymer solar cells, the randomly distributed donor and acceptor components lead to formation of disordered domains and isolated islands, as well as energy-wasting contacts with the electrodes. Such disordered structures combined with low mobilities of holes and electrons in such materials means that many recombine before they can be swept to the electrodes for collection.

Decoding and implementing design principles that produce high fill factors thus represents a significant advance in polymer solar cell technology.

### The paper is titled "Polymer solar cells with enhanced fill factors" and is available at http://www.nature.com/nphoton/journal/vaop/ncurrent/pdf/nphoton.2013.207.pdf.

In addition to Marks, other authors of the paper are Xugang Guo, Nanjia Zhou, Sylvia J. Lou, Jeremy Smith, Daniel B. Tice, Jonathan W. Hennek, Rocío Ponce Ortiz, Shuyou Li, Lin X. Chen, Robert P. H. Chang and Antonio Facchetti, of Northwestern; Juan T. López Navarrete, of the University of Malaga, Spain; and Joseph Strzalka, of Argonne National Laboratory.


ELSE PRESS RELEASES FROM THIS DATE:

1-pot to prep biomass for biofuels

2013-08-14
The advantages of the "one-stop" shop have long been recognized in the retailing and services industries. Similar advantages would also be realized for the biofuels industry with the development of a "one-pot" processing system in which sugars could be extracted from biomass and turned into fuels in a single vat. A major step forward in this goal has now been achieved by researchers with the U.S. Department of Energy (DOE)'s Joint BioEnergy Institute (JBEI) who report the first demonstration of a one-pot, wash-free, process for the ionic liquid pretreatment and saccharification ...

Digital streak camera captures full-color photographs of high-speed objects

2013-08-14
LAGUNA HILLS, California, USA -- Researchers at MetroLaser, Inc., have developed a new design for a digital streak camera that captures full-color images of projectiles traveling up to 3350 m/s, which is 10 times the speed of sound. This system was designed to replace the outdated film-based streak cameras that are still in use at high-speed test tracks. Film-based streak photography records the motion of an object as it passes in front of a camera lens, while the film moves behind a vertical slit aperture during the exposure. The result is a long, continuous composite ...

Children of obese mothers face risk of early death, study shows

2013-08-14
Children born to obese mothers are more likely to die early as adults than those whose mothers were a normal weight, a study has found. The offspring of obese mothers are one-third more likely to die before the age of 55, mainly as a result of heart disease, researchers found. Children born to mothers who were overweight when they became pregnant were also 10 per cent more likely to die prematurely in later life than those born to mothers of a normal weight. The study, carried out by the Universities of Edinburgh and Aberdeen, examined the health records of more ...

Children of obese mothers at greater risk of early heart death as adults

2013-08-14
Children of obese and overweight women have a higher risk of early cardiovascular death as adults, finds a study published on bmj.com today. The findings highlight the urgent need for strategies to prevent obesity in women of childbearing age and the need to assess the offspring of obese mothers for their cardiovascular risk, say the authors. Rates of maternal obesity have risen rapidly in the past two decades. In the United States, about 64% of women of reproductive age are overweight and 35% are obese, with a similar pattern in Europe. Many studies have shown a ...

How bacteria found in mouth may cause colorectal cancer

2013-08-14
Gut microbes have recently been linked to colorectal cancer, but it has not been clear whether and how they might cause tumors to form in the first place. Two studies published by Cell Press on August 14th in the journal Cell Host & Microbe reveal how gut microbes known as fusobacteria, which are found in the mouth, stimulate bad immune responses and turn on cancer growth genes to generate colorectal tumors. The findings could lead to more effective strategies for the early diagnosis, prevention, and treatment of colorectal cancer. "Fusobacteria may provide not only ...

CWRU dental researchers discover how an oral bacterium can trigger colorectal cancer

2013-08-14
Researchers from Case Western Reserve University School of Dental Medicine have discovered how a common oral bacterium can contribute to colorectal cancer, a finding that opens promising new research avenues for the development of approaches to prevent and treat the disease. "We found this cancer is linked to an infection from [the bacterium]," said Yiping Han, professor of periodontics at the dental school and the study's lead investigator. "This discovery creates the potential for new diagnostic tools and therapies to treat and prevent the cancer." The results of ...

Stanford scientists get a handle on what made Typhoid Mary's infectious microbes tick

2013-08-14
STANFORD, Calif. — Stanford University School of Medicine scientists have shown how salmonella — a bacterial menace responsible for hundreds of thousands of deaths each year from typhoid fever and food poisoning — manages to hide out in immune cells, altering their metabolism to its own benefit, much as someone might remodel a newly rented home to suit his own comfort. Salmonella's ability to position itself inside infected people's cells for the long haul can turn them into chronic, asymptomatic carriers who, unknown to themselves or others, spread the infectious organism ...

Growing use of MRIs leading to more invasive breast cancer surgery

2013-08-14
Heavy use of magnetic resonance imaging (MRI) may be leading to unnecessary breast removal in older women with breast cancer, according to a study by Yale School of Medicine researchers in the current issue of Breast Cancer Research and Treatment. "These data are concerning because the long-term benefits associated with bilateral mastectomy for older women with breast cancer are unclear," said the study's lead author Cary Gross. M.D., associate professor of internal medicine at Yale School of Medicine and director of the Cancer Outcomes, Public Policy, and Effectiveness ...

New biomarker could reveal Alzheimer's disease years before onset

2013-08-14
Barcelona, Spain – August 14, 2013 – A study published today reported the identification of what may be the earliest known biomarker associated with the risk of developing Alzheimer's disease (AD). The results suggest that this novel potential biomarker is present in cerebral spinal fluid (CSF) at least a decade before signs of dementia manifest. "If our initial findings can be replicated by other laboratories, the results will change the way we currently think about the causes of Alzheimer's disease," said Dr. Ramon Trullas, research professor at the CSIC Institute of ...

Advancing resistive memory to improve portable electronics

2013-08-14
RIVERSIDE, Calif. — A team at the University of California, Riverside Bourns College of Engineering has developed a novel way to build what many see as the next generation memory storage devices for portable electronic devices including smart phones, tablets, laptops and digital cameras. The device is based on the principles of resistive memory, which can be used to create memory cells that are smaller, operate at a higher speed and offer more storage capacity than flash memory cells, the current industry standard. Terabytes, not gigbytes, will be the norm with resistive ...

LAST 30 PRESS RELEASES:

Scientists model 'true prevalence' of COVID-19 throughout pandemic

New breakthrough to help immune systems in the fight against cancer

Through the thin-film glass, researchers spot a new liquid phase

Administering opioids to pregnant mice alters behavior and gene expression in offspring

Brain's 'memory center' needed to recognize image sequences but not single sights

Safety of second dose of mRNA COVID-19 vaccines after first-dose allergic reactions

Changes in disparities in access to care, health after Medicare eligibility

Use of high-risk medications among lonely older adults

65+ and lonely? Don't talk to your doctor about another prescription

Exosome formulation developed to deliver antibodies for choroidal neovascularization therapy

Second COVID-19 mRNA vaccine dose found safe following allergic reactions to first dose

Plant root-associated bacteria preferentially colonize their native host-plant roots

Rare inherited variants in previously unsuspected genes may confer significant risk for autism

International experts call for a unified public health response to NAFLD and NASH epidemic

International collaboration of scientists rewrite the rulebook of flowering plant genetics

Improving air quality reduces dementia risk, multiple studies suggest

Misplaced trust: When trust in science fosters pseudoscience

Two types of blood pressure meds prevent heart events equally, but side effects differ

New statement provides path to include ethnicity, ancestry, race in genomic research

Among effective antihypertensive drugs, less popular choice is slightly safer

Juicy past of favorite Okinawan fruit revealed

Anticipate a resurgence of respiratory viruses in young children

Anxiety, depression, burnout rising as college students prepare to return to campus

Goal-setting and positive parent-child relationships reduce risk of youth vaping

New research identifies cancer types with little survival improvements in adolescents and young adul

Oncotarget: Replication-stress sensitivity in breast cancer cells

Oncotarget: TERT and its binding protein: overexpression of GABPA/B in gliomas

Development of a novel technology to check body temperature with smartphone camera

The mechanics of puncture finally explained

Extreme heat, dry summers main cause of tree death in Colorado's subalpine forests

[Press-News.org] Plastic solar cells' new design promises bright future
Unprecedented fill factors of 80 percent come close to that of silicon solar cells