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Physics of grain boundaries in polycrystalline photovoltaic semiconductors

Authors :
Tingting Shi
Mowafak Al-Jassim
Yanfa Yan
Zhiwei Wang
Yelong Wu
Naba R. Paudel
Jonathan D. Poplawsky
John Moseley
Chen Li
Wan-Jian Yin
Stephen J. Pennycook
Helio Moutinho
Harvey Guthrey
Source :
Journal of Applied Physics. 117:112807
Publication Year :
2015
Publisher :
AIP Publishing, 2015.

Abstract

Thin-film solar cells based on polycrystalline Cu(In,Ga)Se2 (CIGS) and CdTe photovoltaic semiconductors have reached remarkable laboratory efficiencies. It is surprising that these thin-film polycrystalline solar cells can reach such high efficiencies despite containing a high density of grain boundaries (GBs), which would seem likely to be nonradiative recombination centers for photo-generated carriers. In this paper, we review our atomistic theoretical understanding of the physics of grain boundaries in CIGS and CdTe absorbers. We show that intrinsic GBs with dislocation cores exhibit deep gap states in both CIGS and CdTe. However, in each solar cell device, the GBs can be chemically modified to improve their photovoltaic properties. In CIGS cells, GBs are found to be Cu-rich and contain O impurities. Density-functional theory calculations reveal that such chemical changes within GBs can remove most of the unwanted gap states. In CdTe cells, GBs are found to contain a high concentration of Cl atoms. Cl atoms donate electrons, creating n-type GBs between p-type CdTe grains, forming local p-n-p junctions along GBs. This leads to enhanced current collections. Therefore, chemical modification of GBs allows for high efficiency polycrystalline CIGS and CdTe thin-film solar cells.

Details

ISSN :
10897550 and 00218979
Volume :
117
Database :
OpenAIRE
Journal :
Journal of Applied Physics
Accession number :
edsair.doi...........91da636faffa7baf5108764d92544efd