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

Stanford study could lead to paradigm shift in organic solar cell research

2013-11-20
(Press-News.org) Contact information: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
Stanford study could lead to paradigm shift in organic solar cell research

Organic solar cells have long been touted as lightweight, low-cost alternatives to rigid solar panels made of silicon. Dramatic improvements in the efficiency of organic photovoltaics have been made in recent years, yet the fundamental question of how these devices convert sunlight into electricity is still hotly debated.

Now a Stanford University research team is weighing in on the controversy. Their findings, published in the Nov. 17 issue of the journal Nature Materials, indicate that the predominant working theory is incorrect, and could steer future efforts to design materials that boost the performance of organic cells.

"We know that organic photovoltaics are very good," said study coauthor Michael McGehee, a professor of materials science and engineering at Stanford. "The question is, why are they so good? The answer is controversial."

A typical organic solar cell consists of two semiconducting layers made of plastic polymers and other flexible materials. The cell generates electricity by absorbing particles of light, or photons.

When the cell absorbs light, a photon knocks out an electron in a polymer atom, leaving behind an empty space, which scientists refer to as a hole. The electron and the hole immediately form a bonded pair called an exciton. The exciton splits, allowing the electron to move independently to a hole created by another absorbed photon. This continuous movement of electrons from hole to hole produces an electric current.

In the study, the Stanford team addressed a long-standing debate over what causes the exciton to split.

"To generate a current, you have to separate the electron and the hole," said senior author Alberto Salleo, an associate professor of materials science and engineering at Stanford. "That requires two different semiconducting materials. If the electron is attracted to material B more than material A, it drops into material B. In theory, the electron should remain bound to the hole even after it drops.

"The fundamental question that's been around a long time is, how does this bound state split?"

Some like it hot

One explanation widely accepted by scientists is known as the "hot exciton effect." The idea is that the electron carries extra energy when it drops from material A to material B. That added energy gives the excited ("hot") electron enough velocity to escape from the hole.

But that hypothesis did not stand up to experimental tests, according to the Stanford team.

"In our study, we found that the hot exciton effect does not exist," Salleo said. "We measured optical emissions from the semiconducting materials and found that extra energy is not required to split an exciton."

So what actually causes electron-hole pairs to separate?

"We haven't really answered that question yet," Salleo said. "We have a few hints. We think that the disordered arrangement of the plastic polymers in the semiconductor might help the electron get away."

In a recent study, Salleo discovered that disorder at the molecular level actually improves the performance of semiconducting polymers in solar cells. By focusing on the inherent disorder of plastic polymers, researchers could design new materials that draw electrons away from the solar cell interface where the two semiconducting layers meet, he said.

"In organic solar cells, the interface is always more disordered than the area further away," Salleo explained. "That creates a natural gradient that sucks the electron from the disordered regions into the ordered regions. "

Improving energy efficiency

The solar cells used in the experiment have an energy-conversion efficiency of about 9 percent. The Stanford team hopes to improve that performance by designing semiconductors that take advantage of the interplay between order and disorder.

"To make a better organic solar cell, people have been looking for materials that would give you a stronger hot exciton effect," Salleo said. "They should instead try to figure out how the electron gets away without it being hot. This idea is pretty controversial. It's a fundamental shift in the way people think about photocurrent generation."



INFORMATION:

Other authors of the paper are Koen Vandewal (lead author), Erik Hoke, William Mateker, Jason Bloking and George Burkhard of Stanford; Steve Albrecht, Marcel Schubert and Dieter Neher of the University of Potsdam; Johannes Widmer and Moritz Riede of the Institute for Applied Photophysics (IAPP); Jessica Douglas and Jean Frechet of the University of California-Berkeley; Aram Amassian of the King Abdullah University of Science and Technology (KAUST); and Alan Sellinger of the Colorado School of Mines and the University of Oxford. Author Kenneth Graham has a joint postdoctoral fellowship with Stanford and KAUST.

Support for the study was provided by the Stanford Center for Advanced Molecular Photovoltaics and the U.S. Department of Energy.

This article was written by Mark Shwartz, Precourt Institute for Energy, Stanford University.



ELSE PRESS RELEASES FROM THIS DATE:

New study finds no benefit to selecting dose of blood thinner based on patients' genetic makeup

2013-11-20
New study finds no benefit to selecting dose of blood thinner based on patients' genetic makeup Largest randomized, multi-center controlled trial of gene-based strategy for warfarin dosing also found better outcome for African ...

Edoxaban effective in preventing stroke, reducing bleeding and cardiovascular death in patients with atrial fibrillation

2013-11-20
Edoxaban effective in preventing stroke, reducing bleeding and cardiovascular death in patients with atrial fibrillation Boston, MA – According to the United States Centers for Disease Control and Prevention, over 800,000 ...

Bedroom access to screen-based media may contribute to sleep problems in boys with autism, MU researchers find

2013-11-20
Bedroom access to screen-based media may contribute to sleep problems in boys with autism, MU researchers find Having bedroom access to television, computers or video games is linked to less sleep in boys with autism spectrum disorder (ASD), a team of University ...

Higher emotional intelligence leads to better decision-making

2013-11-20
Higher emotional intelligence leads to better decision-making Toronto – The anxiety people feel making investment decisions may have more to do with the traffic they dealt with earlier than the potential consequences they face with the ...

Enhancing battery performance

2013-11-20
Enhancing battery performance In APL Materials paper, researchers show how to keep cathode material 'in line' to enhance performance WASHINGTON D.C. Nov. 19, 2013 -- The ever-increasing market for portable electronic devices such as laptops, cell phones ...

The human health costs of losing natural systems: Quantifying Earth's worth to public health

2013-11-20
The human health costs of losing natural systems: Quantifying Earth's worth to public health Scientists urge focus on new branch of environmental health A new paper from members of the HEAL (Health & Ecosystems: Analysis of Linkages) consortium delineates a new ...

Obesity and nutrition are keys to avoiding metabolic syndrome

2013-11-20
Obesity and nutrition are keys to avoiding metabolic syndrome MINNEAPOLIS, MN – November 19, 2013 – Data reported by the Hearts Beat Back: The Heart of New Ulm Project reinforce the positive influence of lifestyle factors in mitigating risks that ...

Tuesday, Nov. 19, 2013 news tips

2013-11-20
Tuesday, Nov. 19, 2013 news tips Disappearing stent continues protection for 3 years Propping open clogged heart arteries with a "disappearing stent" has worked well for three years in the first people implanted with the unique device, according to research presented ...

Holistic cell design leads to high-performance, long cycle-life Li/S battery

2013-11-20
Holistic cell design leads to high-performance, long cycle-life Li/S battery Berkeley Lab battery a promise for mobile, and eventually, electric vehicles with 300-mile range Researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory ...

Holiday shopping online: Don't overwhelm consumers with too many images

2013-11-20
Holiday shopping online: Don't overwhelm consumers with too many images If presented with looking at an image or reading a paragraph describing the same product, consumers often prefer the visual option. However, according to a new study in the Journal ...

LAST 30 PRESS RELEASES:

Powerful new tool promises major advances in cancer treatment

Inflammation and the brain: how immune activity can alter mood and fuel anxiety

Researchers demonstrate the UK’s first long-distance ultra-secure communication over a quantum network

One in 3,000 people at risk of punctured lung from faulty gene – almost 100 times higher than previous estimate

Creativity and problem-solving: How design thinking transforms university teaching

American College of Cardiology recognizes 2025 Young Investigator Award recipients

Coding differences in Medicare Advantage plans led to $33 billion in excess revenue to insurers

CAS and Cleveland Clinic collaborate to accelerate research through advanced AI and quantum computing

Fees can help the FDA ensure food safety

Medically tailored meal programs could yield significant health care savings across 49 US states

Sarah Sjöström, MSN, RN, ACNP-BC, named chief nursing officer at Hebrew SeniorLife

Transparency in government is good for global health

Dust in the Wind: How cities alter natural airborne particles

Stephen Hauser wins breakthrough prize for role in redefining MS

Childhood experiences shape the brain’s white matter with cognitive effects seen years later

Hantavirus in Madagascar linked to black rats in agricultural areas

Clockwork, just for antibiotic resistance?

Tabbye M. Chavous named new Executive Director of the American Educational Research Association

Mindfulness and cognitive behavioral therapy improve chronic low back pain

Proteins shown to act as ‘guardians’ to keep cells’ energy making mitochondria safe

Letting your mind wander can sometimes improve learning

Exploring how people interact with virtual avatars

Hospital addiction consultation service increases medication treatment for opioid use disorder

Newly discovered PNS microglia found to regulate neuron size

Brain’s own repair mechanism: New neurons may reverse damage in Huntington’s disease

Neighborhood disadvantage, individual experiences of racism, and breast cancer survival

Cardioprotective glucose-lowering agents and dementia risk

Two-thirds of U.S. adolescent minors are impacted by state abortion restrictions

GLP-1RA and SGLT2i medications for type 2 diabetes and Alzheimer disease and related dementias

In the search for life on exoplanets, finding nothing is something too

[Press-News.org] Stanford study could lead to paradigm shift in organic solar cell research