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:

Global trends and cross-country inequalities of acute hepatitis E in the elderly, 1990–2021

New catalyst enables triple-efficiency decomposition of ammonia for clean hydrogen

FAU Harbor Branch receives $1M grant to study gulf’s mesophotic coral habitats

WSU study provides detailed look at the declining groundwater in regional aquifer system

Creatine may help the brain, not just muscles

Teams develop CO₂ capture-conversion tandem system adaptable to a wide range of CO₂ concentrations

Endocrine Society proposes research efforts to improve treatment options for people with type 1 diabetes

In menopause, sleep is vitally important for women’s long-term heart health, study finds

Why do some brain regions resist Alzheimer’s?

Like humans, monkeys are attracted to videos showing conflict

Dr. Richard M. Peterson elected 39th president of American Society for Metabolic and Bariatric Surgery

Addressing “spay-neuter syndrome" with testosterone restoration for neutered male dogs

The ACMG releases 2025 update to secondary findings gene list; SF v3.3

More rural, minoritized people get amputations – AI gets closer to why

First look at defects in single-crystal indium gallium zinc oxide could fix persistent display instability

Understanding childhood maltreatment and its effect on biological aging

Turning step-growth into chain-growth with click polymerization

Researchers find surgical technique reduced risk of early preterm birth for patients with cervical insufficiency

Novel nanostructures in blue sharks reveal their remarkable potential for dynamic colour-change

People with ‘young brains’ outlive ‘old-brained’ peers, Stanford Medicine scientists find

Make-your-own weight-loss drug using an innovative genome editing approach

Cancer is extremely rare in turtles, finds a new study

AI used to create protein that kills E. coli

Major autism study uncovers biologically distinct subtypes, paving the way for precision diagnosis and care

Study shows how AI could help pathologists match cancer patients to the right treatments—faster and more efficiently

Implantable device could save diabetes patients from dangerously low blood sugar

Need a new 3D material? Build it with DNA

New study reveals subclasses of autism by linking traits to genetics

The right mix and planting pattern of trees enhance forest productivity and services

Coral calcification benefits from human hormone injections

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