Navigation Links
Stanford study could lead to paradigm shift in organic solar cell research
Date:11/19/2013

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."


'/>"/>

Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
Source:Eurekalert  

Related biology technology :

1. Stanford engineers use nanophotonics to reshape on-chip computer data transmission
2. Stanford engineers weld nanowires with light
3. Unzipped carbon nanotubes could help energize fuel cells and batteries, Stanford scientists say
4. Stanford engineers perfecting carbon nanotubes for highly energy-efficient computing
5. Stanford scientists spark new interest in the century-old Edison battery
6. Stanford faculty awarded $2.2 million for innovative energy research
7. Taming mavericks: Stanford researchers use synthetic magnetism to control light
8. NREL and Stanford team up on peel-and-stick solar cells
9. Stanford scientists create a low-cost, long-lasting water splitter made of silicon and nickel
10. Positive Clinical Study Results for BSPs HyperQ Technology
11. 15-Minute Data From Phase 3 Study of Avanafil Featured as a Late Breaking Abstract at SMSNA Annual Meeting
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
Stanford study could lead to paradigm shift in organic solar cell research
(Date:12/2/2016)... ... , ... DrugDev believes the only way to achieve real change ... three tenets were on display at the 2nd Annual DrugDev User Summit (hosted by ... and site organizations to discuss innovation and the future of clinical research. , ...
(Date:12/2/2016)... ... December 02, 2016 , ... Robots will storm the Prudential Center in Boston, ... The event, which is held on the United Nations International Day of Persons with ... into the workplace. Suitable Technologies is partnering with NTI to showcase how technology can ...
(Date:12/2/2016)... leader in rapid infectious disease tests, introduced the Company,s newest product, the INSTI HIV ... http://photos.prnewswire.com/prnh/20161201/444905 ) Continue Reading ... ... , bioLytical was invited by the Clinton Health ... Self Test to 350 pharmacy representatives in Nairobi and Mombasa, ...
(Date:11/30/2016)... , November 30, 2016 ... a few players hold a dominant share in the ... River Laboratories International, Inc., and Merck KGaA, held a ... 2015. Transparency Market Research observes that these companies are ... on development products that are do not require rabbit ...
Breaking Biology Technology:
(Date:11/30/2016)... CHICAGO , Nov. 30, 2016  higi ... a new partnership initiative targeting national brands, industry ... and reward their respective audiences for taking steps ... Since its inception in 2012, higi has built ... US, impacting over 38 million people who have ...
(Date:11/24/2016)... -- Cercacor today introduced Ember TM Sport Premium ... measure hemoglobin, Oxygen Content, Oxygen Saturation, Perfusion Index, ... approximately 30 seconds. Smaller than a smartphone, using only ... key data about their bodies to help monitor these ... Hemoglobin carries oxygen to muscles. When hemoglobin and ...
(Date:11/17/2016)... Nov. 17, 2016 Global Market Watch: ... (Disease-Based Banks, Population-Based Banks and Academics) market is to witness ... Private Biobanks shows the highest Compounded Annual Growth Rate (CAGR) ... region during the analysis period 2014-2020. North America ... 9.95% followed by Europe at 9.56% ...
Breaking Biology News(10 mins):