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Title: Physics of grain boundaries in polycrystalline photovoltaic semiconductors

Thin-film solar cells based on polycrystalline Cu(In,Ga)Se{sub 2} (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.
Authors:
; ; ; ;  [1] ;  [2] ;  [3] ;  [1] ;  [4] ; ; ; ;  [5] ;  [6]
  1. Department of Physics and Astronomy and Wright Center for Photovoltaics Innovation and Commercialization, The University of Toledo, Ohio 43606 (United States)
  2. Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
  3. The Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)
  4. (United States)
  5. National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)
  6. Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States)
Publication Date:
OSTI Identifier:
22399288
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 11; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CADMIUM TELLURIDES; CHARGE CARRIERS; CONCENTRATION RATIO; DENSITY FUNCTIONAL METHOD; DISLOCATIONS; EFFICIENCY; ELECTRONS; GRAIN BOUNDARIES; PHOTOVOLTAIC EFFECT; POLYCRYSTALS; P-TYPE CONDUCTORS; RECOMBINATION; SEMICONDUCTOR JUNCTIONS; SOLAR CELLS; THIN FILMS