Thoughts on the microstructure of polycrystalline thin film CuInSe2 and its impact on material and device performance

Tuttle, J. R.; Albin, D.; Noufi, R.

doi:10.1016/0379-6787(91)90034-m

Cited by 116 publications

(53 citation statements)

References 15 publications

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“…This Cu-poor surface composition is well-known for highefficiency Cu-poor processed CIGSe samples. [46][47][48] The potential impact of the presence of Na on the chemical surface structure is shown in Fig. 5(b).…”

Section: Surface Compositionmentioning

confidence: 99%

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Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure

Song

Caballero

Félix

et al. 2012

Journal of Applied Physics

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The following article appeared in Journal of Applied Physics 111.3 (2012): 034903 and may be found at http://scitation.aip.org/content/aip/journal/jap/111/3/10.1063/1.3679604Na has deliberately been incorporated into Cu(In,Ga)Se2 (CIGSe) chalcopyrite thin-film solar cell absorbers deposited on Mo-coated polyimide flexible substrates by adding differently thick layers of NaF in-between CIGSe absorber and Mo back contact. The impact of Na on the chemical and electronic surface structure of CIGSe absorbers with various Cu-contents deposited at comparatively low temperature (420 C) has been studied using x-ray photoelectron and x-ray excited Auger electron spectroscopy. We observe a higher Na surface content for the Cu-richer CIGSe samples and can distinguish between two different chemical Na environments, best described as selenide-like and oxidized Na species, respectively. Furthermore, we find a Cu-poor surface composition of the CIGSe samples independent of Na content and - for very high Na contents - indications for the formation of a (Cu,Na)-(In,Ga)-Se like compound. With increasing Na surface content, also a shift of the photoemission lines to lower binding energies could be identified, which we interpret as a reduction of the downward band bending toward the CIGSe surface explained by the Na-induced elimination of In Cu defects.X.S., R.F., D.G., R.G.W., and M.B. are grateful to the Helmholtz-Association for financial support (VH-NG-423). R.F. also acknowledges the support by the German Academic Exchange Agency (DAAD; 331 4 04 002)

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Section: Surface Compositionmentioning

confidence: 99%

“…D) was explained in the past by the formation of an ordered defect compound (ODC) layer 46,47 or by surface reconstruction. 51,52 While according to first-principles calculations the ODC can be considered as periodic repetition of the charge compensated (2 V Cu À þ In Cu 2þ ) defect complex (as described in Ref.…”

Section: E Binding Energy Shiftmentioning

confidence: 99%

Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure

Song

Caballero

Félix

et al. 2012

Journal of Applied Physics

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“…for thermal co-evaporation or two-stage processes. 5,6,8 For three-stage processes, the secondary phase is thought to be consumed during the third stage by simultaneous In, Ga, and Se deposition. The third stage also leads to higher efficiencies by reducing the Cu amount…”

mentioning

confidence: 99%

Evidence for Cu2–xSe platelets at grain boundaries and within grains in Cu(In,Ga)Se2 thin films

Sanli

Ramasse

Mainz

et al. 2017

Applied Physics Letters

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Cu(In,Ga)Se2 (CIGS)-based solar cells reach high power-conversion efficiencies of above 22%. In this work, a three-stage co-evaporation method was used for their fabrication. During the growth stages, the stoichiometry of the absorbers changes from Cu-poor ([Cu]/([In] + [Ga]) < 1) to Cu-rich ([Cu]/([In] + [Ga]) > 1) and finally becomes Cu-poor again when the growth process is completed. It is known that, according to the Cu-In-Ga-Se phase diagram, a Cu-rich growth leads to the presence of Cu2–xSe (x = 0–0.25), which is assumed to assist in recrystallization, grain growth, and defect annihilation in the CIGS layer. So far, Cu2–xSe precipitates with spatial extensions on the order of 10–100 nm have been detected only in Cu-rich CIGS layers. In the present work, we report Cu2–xSe platelets with widths of only a few atomic planes at grain boundaries and as inclusions within grains in a polycrystalline, Cu-poor CIGS layer, as evidenced by high-resolution scanning transmission electron microscopy (STEM). The chemistry of the Cu–Se secondary phase was analyzed by electron energy-loss spectroscopy, and STEM image simulation confirmed the identification of the detected phase. These results represent additional experimental evidence for the proposed topotactical growth model for Cu–Se–assisted CIGS thin-film formation under Cu-rich conditions.

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“…16 This additional reflection originates from the different cation ordering and the presence of Cu-vacancies in the ODC-related structures. 3 Fitting of the (112) peak shows the co-existence of the (1:1:2) and (1:3:5) phases in the film with Z ¼ 0.3, while the contribution of the ODC phase in the XRD peak increases with the increase of the Z-value. The film with Z ¼ 0.63 shows the diffraction peaks that correspond to the almost single phase ODC (CuGa 3 Se 5 phase) with no evidence of any (1:1:2) chalcopyrite phase in the structure.…”

Section: þ2mentioning

confidence: 99%

“…1 Deviation from the ideal stoichiometry of this material is reported to form some secondary phases, preferably segregated on the surface of the film. In Particular, the formation of the Cu(In,Ga) 3 Se 5, Cu(In,Ga) 2 Se 3.5 , etc., phases on the surface of the slightly Cu-poor film and also in the stoichiometric film is a commonly observed phenomenon in CIGS material grown by various methods 2,3 and is believed to have some positive impact on the low-gap-based device performance, mainly due to the bandgap widening and type inversion at the near surface. In these secondary phases, the vacancies might orderly occupy particular crystallographic sites in the structure to satisfy the four electrons per site rule.…”

Section: Introductionmentioning

confidence: 99%

Cu-dependent phase transition in polycrystalline CuGaSe2 thin films grown by three-stage process

Islam

Yamada

Sakurai

et al. 2011

Journal of Applied Physics

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The Cu-dependent phase transition in polycrystalline CuGaSe 2 thin films has been studied by an electron probe micro-analyzer (EPMA) and the synchrotron x-ray diffraction method. A Cu-deficiency parameter, Z, defined as (1 À Cu/Ga) was used to study the phase transition. Upon increasing the Z-value, the composition of the films on the Cu 2 Se-Ga 2 Se 3 pseudo binary tie line was found to shift from the stoichiometric CuGaSe 2 (1:1:2) (Z ¼ 0) to the Ga-rich composition through the formation of several ordered defect compounds.The structural modification in the Cu-poor CuGaSe 2 film has been investigated by the synchrotron x-ray diffraction method. The existence of the Cu-poor surface phase over the near-stoichiometric bulk CuGaSe 2 film was confirmed by the fitting of the accelerated voltage dependent EPMA data.

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Thoughts on the microstructure of polycrystalline thin film CuInSe2 and its impact on material and device performance

Cited by 116 publications

References 15 publications

Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure

Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure

Evidence for Cu2–xSe platelets at grain boundaries and within grains in Cu(In,Ga)Se2 thin films

Cu-dependent phase transition in polycrystalline CuGaSe2 thin films grown by three-stage process

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