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# Antisite traps and metastable defects in Cu(In,Ga)Se2 thin-film solar cells studied by screened-exchange hybrid density functional theory

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### Abstract

Electronic structure calculations within screened-exchange hybrid density functional theory show that Cu(In,Ga) antisites in both CuInSe2 and CuGaSe2 are localized hole traps, which can be attributed to the experimentally observed N2 level. In contrast, GaCu antisites and their defect complexes with copper vacancies exhibit an electron trap level, which can limit the open-circuit voltage and efficiency in Ga-rich Cu(In,Ga)Se2 alloys. Low-temperature photoluminescence measurements in CuGaSe2 thin-film solar cells show a free-to-bound transition at an energy of 1.48 eV, in very good agreement with the calculated transition energy for the GaCu antisite. Since the intrinsic DX center does not exhibit a pinning level within the band gap of CuInSe2, metastable DX behaviour can only be expected for GaCu antisites.

### Most cited references15

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### Defect physics of theCuInSe2chalcopyrite semiconductor

(1998)
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### n-type doping ofCuInSe2andCuGaSe2

(2005)
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### Intrinsic$$DX$$Centers in Ternary Chalcopyrite Semiconductors

(2008)
In III-V and II-VI semiconductors, certain nominally electron-donating impurities do not release electrons but instead form deep electron-traps known as "DX centers." While in these compounds, such traps occur only after the introduction of foreign impurity atoms, we find from first-principles calculations that in ternary I-III-VI2 chalcopyrites like CuInSe2 and CuGaSe2, DX-like centers can develop without the presence of any extrinsic impurities. These intrinsic DX centers are suggested as a cause of the difficulties to maintain high efficiencies in CuInSe2-based thin-film solar-cells when the band gap is increased by addition of Ga.
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### Author and article information

###### Journal
11 May 2012
###### Article
1205.2556