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:5/26/2017)... Linda, Ca (PRWEB) , ... May 25, 2017 ... ... to truly understanding the full process behind each occurrence. Live cell imaging using ... In this webinar, the use of automated fluorescence microscopy methods will be discussed, ...
(Date:5/24/2017)... Utah (PRWEB) , ... May 24, 2017 , ... ... the selection and implementation of CLEARAS Water Recovery’s Advanced Biological Nutrient Recovery (ABNR™) ... key component of a $24 million plant upgrade to sustainably meet current and ...
(Date:5/24/2017)... ... May 24, 2017 , ... Patient Monitoring and ... Wi-Fi connectivity to reduce the amount of wiring in a healthcare facility and ... mobile devices including infusion pumps, heart and hypertension monitoring, glucose monitoring, and other ...
(Date:5/23/2017)... , ... May 23, 2017 , ... A recent survey ... most troublesome and difficult to control weed in 12 categories of broadleaf crops, fruits ... 200 weed scientists across the U.S. and Canada participated in the 2016 survey, the ...
Breaking Biology Technology:
(Date:3/20/2017)... 20, 2017 At this year,s CeBIT Chancellor Dr. ... manufacturer DERMALOG. The Chancellor came to the DERMALOG stand together with the ... year,s CeBIT partner country. At the largest German biometrics company the two ... face and iris recognition as well as DERMALOG´s multi-biometrics system.   ... ...
(Date:3/16/2017)... 16, 2017 CeBIT 2017 - Against identity fraud with DERMALOG solutions ... ... Used combined in one project, multi-biometric solutions provide a crucial contribution against ... Used combined in one project, ... ...
(Date:3/9/2017)... Australia , March 9, 2017 4Dx ... prestigious World Lung Imaging Workshop at the University of ... was invited to deliver the latest data to world ... recognised event brings together leaders at the forefront of ... in lung imaging. "The quality of ...
Breaking Biology News(10 mins):