Featured Research

from universities, journals, and other organizations

Light-induced degradation in amorphous silicon thin film solar cells

Date:
February 13, 2014
Source:
Helmholtz-Zentrum Berlin für Materialien und Energie
Summary:
Researchers have taken a leap forward towards a deeper understanding of an undesired effect in thin film solar cells based on amorphous silicon -- one that has puzzled the scientific community for the last 40 years. The researchers were able to demonstrate that tiny voids within the silicon network are partly responsible for reducing solar cell efficiency by some 10 to 15 percent as soon as you start using them.

In the initial state (left), the voids' internal surfaces are saturated with hydrogen atoms so that no defects are observed. Light-induced charge carriers (h+) destabilize atomic bonds. The breaking of atomic bonds causes defects (indicated by the vertical arrows on the right hand side), which translates to reduced solar cell efficiency.
Credit: Image courtesy of Helmholtz-Zentrum Berlin für Materialien und Energie

Researchers at the Helmholtz Center Berlin (HZB) have taken a leap forward towards a deeper understanding of an undesired effect in thin film solar cells based on amorphous silicon -- one that has puzzled the scientific community for the last 40 years. The researchers were able to demonstrate that tiny voids within the silicon network are partly responsible for reducing solar cell efficiency by some 10 to 15 percent as soon as you start using them.

Amorphous silicon thin film solar cells are considered a promising alternative to solar cells based on highly purified silicon wafers, which have been dominating photovoltaic power generation. A major advantage of amorphous silicon thin film photovoltaics, where a glass substrate is coated with a light active material less than a thousandth of a millimeter thick, is that the cell fabrication is considerably simpler and much less costly than in the case of conventional crystalline silicon solar cells. On the other hand, a potential disadvantage is the low conversion efficiency from solar energy to electricity. Because of the disordered nature of amorphous silicon, solar cells are subject to the Staebler-Wronski effect, which reduces the solar cell efficiency by up to 15 percent within the first 1000 hours.

This undesired effect is triggered by internal annihilation -- known in physics as recombination -- of charge that has not been extracted from the solar cell. The released recombination energy induces defects in the amorphous network -- which is why this effect is not observed in crystalline wafer solar cells. "However, where defects are produced in the material and whether voids of nanoscale size play a role in all this has not been understood -- until now, that is," says HZB's own Matthias Fehr of the Institute for Silicon Photovoltaics. Fehr together with his HZB colleagues, scientists from Jülich Research Center and the Free University of Berlin have now made major strides towards unraveling this mystery.

Since the defects that form exhibit paramagnetic properties, they have a characteristic magnetic fingerprint, which depends on their microscopic environment. The Berlin researchers were able to identify this fingerprint using electron-paramagnetic resonance (EPR) spectroscopy and electron-spin echo (ESE) experiments. With the help of these highly sensitive techniques, they determined that defects in amorphous silicon actually come in two types: those that are uniformly distributed and those that are concentrated in clusters on internal surfaces of small voids -- known in scientific circles as microvoids -- which form within the material during the solar cell manufacturing process. "Our guess is that clusters of defects are generated on the internal walls of microvoids, which have a diameter of a mere one to two nanometers," explains HZB physicist Fehr. "Our findings seem to suggest that microvoids most likely contribute to light-induced degradation of amorphous silicon thin film solar cells. For us, it's been a leap forward towards a better understanding of the microscopic mechanism of light-induced degradation," says Fehr who, in 2013, spent a year conducting research in the US as a Feodor Lynen Scholar of the Alexander Humboldt Foundation. A new series of experiments has been designed to allow the Berlin researchers to glean further insights into the atomic and electronic processes of the Staebler-Wronski effect, named for the two scientists who first discovered it.

The work is part of the EPR-Solar network funded by the German Federal Ministry for Education and Research and the HZB's and FUB's Berlin Joint EPR Lab. According to the head of the project, Prof. Dr. Klaus Lips, "this is one of the major projects of one of the HZB's newest research departments, which is currently in the founding stage and whose mission is the fundamental physical characterization of energy materials with the goal of making an important contribution to the energy transition."


Story Source:

The above story is based on materials provided by Helmholtz-Zentrum Berlin für Materialien und Energie. Note: Materials may be edited for content and length.


Journal Reference:

  1. Fehr, M., Schnegg, A., Rech, B., Astakhov, O., Finger, F., Bittl, R., Teutloff, C., Lips, K. Metastable defect formation at microvoids identified as a source of light-induced degradation in a-Si:H. Phys. Rev. Lett., 2014 DOI: 10.1103/PhysRevLett.112.066403

Cite This Page:

Helmholtz-Zentrum Berlin für Materialien und Energie. "Light-induced degradation in amorphous silicon thin film solar cells." ScienceDaily. ScienceDaily, 13 February 2014. <www.sciencedaily.com/releases/2014/02/140213122404.htm>.
Helmholtz-Zentrum Berlin für Materialien und Energie. (2014, February 13). Light-induced degradation in amorphous silicon thin film solar cells. ScienceDaily. Retrieved July 24, 2014 from www.sciencedaily.com/releases/2014/02/140213122404.htm
Helmholtz-Zentrum Berlin für Materialien und Energie. "Light-induced degradation in amorphous silicon thin film solar cells." ScienceDaily. www.sciencedaily.com/releases/2014/02/140213122404.htm (accessed July 24, 2014).

Share This




More Matter & Energy News

Thursday, July 24, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Robot Parking Valet Creates Stress-Free Travel

Robot Parking Valet Creates Stress-Free Travel

AP (July 23, 2014) — 'Ray' the robotic parking valet at Dusseldorf Airport in Germany lets travelers to avoid the hassle of finding a parking spot before heading to the check-in desk. (July 23) Video provided by AP
Powered by NewsLook.com
Boeing Ups Outlook on 52% Profit Jump

Boeing Ups Outlook on 52% Profit Jump

Reuters - Business Video Online (July 23, 2014) — Commercial aircraft deliveries rose seven percent at Boeing, prompting the aerospace company to boost full-year profit guidance- though quarterly revenues missed analyst estimates. Bobbi Rebell reports. Video provided by Reuters
Powered by NewsLook.com
Europe's Car Market on the Rebound?

Europe's Car Market on the Rebound?

Reuters - Business Video Online (July 23, 2014) — Daimler kicks off a round of second-quarter earnings results from Europe's top carmakers with a healthy set of numbers - prompting hopes that stronger sales in Europe will counter weakness in emerging markets. Hayley Platt reports. Video provided by Reuters
Powered by NewsLook.com
9/11 Commission Members Warn of Terror "fatigue" Among American Public

9/11 Commission Members Warn of Terror "fatigue" Among American Public

Reuters - US Online Video (July 22, 2014) — Ten years after releasing its initial report, members of the 9/11 Commission warn of the "waning sense of urgency" in combating terrorists attacks. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins