TY - JOUR
T1 - Physics of grain boundaries in polycrystalline photovoltaic semiconductors
AU - Yan, Yanfa
AU - Yin, Wan Jian
AU - Wu, Yelong
AU - Shi, Tingting
AU - Paudel, Naba R.
AU - Li, Chen
AU - Poplawsky, Jonathan
AU - Wang, Zhiwei
AU - Moseley, John
AU - Guthrey, Harvey
AU - Moutinho, Helio
AU - Pennycook, Stephen J.
AU - Al-Jassim, Mowafak M.
N1 - Publisher Copyright:
© 2015 AIP Publishing LLC.
PY - 2015/3/21
Y1 - 2015/3/21
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84924941661&partnerID=8YFLogxK
U2 - 10.1063/1.4913833
DO - 10.1063/1.4913833
M3 - Article
AN - SCOPUS:84924941661
SN - 0021-8979
VL - 117
JO - Journal of Applied Physics
JF - Journal of Applied Physics
IS - 11
M1 - 112807
ER -