Na-induced effects on the electronic structure and composition of Cu(In,Ga)Se2 thin-film surfaces

Heske, C.; Fink, R.; Umbach, E.; Riedl, W.; Karg, F.

doi:10.1063/1.115783

Cited by 90 publications

(68 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The former is due to the well-known diffusion of Na from the soda-lime glass substrate through the Mo and CIGSe layers, 13 the latter indicates an IMN-to-UNLV sample transfer with minimal sample contamination. Upon In 2 S 3 deposition, S-related peaks can also be observed.…”

Section: ͑͒mentioning

confidence: 99%

Nondestructive depth-resolved spectroscopic investigation of the heavily intermixed In2S3/Cu(In,Ga)Se2 interface

Bär

Barreau

Couzinié-Devy

et al. 2010

Applied Physics Letters

Self Cite

View full text Add to dashboard Cite

͑͒The chemical structure of the interface between a nominal In 2 S 3 buffer and a Cu͑In, Ga͒Se 2 ͑CIGSe͒ thin-film solar cell absorber was investigated by soft x-ray photoelectron and emission spectroscopy. We find a heavily intermixed, complex interface structure, in which Cu diffuses into ͑and Na through͒ the buffer layer, while the CIGSe absorber surface/interface region is partially sulfurized. Based on our spectroscopic analysis, a comprehensive picture of the chemical interface structure is proposed. ͓͔ Cu͑In, Ga͒Se 2 ͑CIGSe͒ thin-film solar cells with an n + -ZnO/i-ZnO/CdS/CIGSe/Mo/glass device structure have reached efficiencies of 20%.1 To replace the CdS layer by a nontoxic, more transparent buffer, and the conventionally used chemical bath deposition by a technique allowing inline processing, In 2 S 3 layers have been deposited by physical vapor deposition, 2 sputtering, 3 atomic layer deposition, 4 and spray ion layer gas reaction. 5The In 2 S 3 /CIGSe interface has been previously investigated by different destructive depth-profiling techniques, 2,6 high-resolution transmission electron microscopy and energy dispersive x-ray analysis, 7 and x-ray photoelectron spectroscopy ͑XPS͒. 4,8,9 At ͑post-͒deposition annealing temperatures necessary for high device efficiencies ͑200-250°C͒, a pronounced diffusion of Cu and Na from the CIGSe/Mo/glass substrate into the nominal In 2 S 3 buffer layer was found in these studies. However, a complete picture of the chemical interface structure is still missing. In this paper, we will report on the characterization of the In 2 S 3 /CIGSe interface by a combination of nondestructive techniques ͓XPS and soft x-ray emission spectroscopy ͑XES͔͒, deliberately varying the probing depth. Our measurements result in a depth-resolved picture of the interface in unprecedented detail.In 2 S 3 /CIGSe structures were prepared at IMN on Mo/ glass substrates. 10 The absorber layers were dipped in NH 3 solution ͑1 M, room temperature, 1 min͒ prior to the In 2 S 3 buffer layer deposition by thermal coevaporation of elemental indium and sulfur at 200°C substrate temperature. To vary the In 2 S 3 thickness, different deposition times were used. The standard 80 nm buffer used in solar cells is prepared in 10 min ͑called "1/1" in the following͒. For reference, an In 2 S 3 layer, different In 2 S 3 : Cu standards, and a CuInS 2 ͑CIS͒ absorber 11 were deposited on Mo/glass substrates. After preparation, all samples were sealed in polyethylene bags filled with dry N 2 and desiccant for transport. At UNLV the samples were transferred into the analysis chamber ͑base pressure Ͻ5 ϫ 10 −10 mbar͒ without air exposure. XPS was performed using Mg K ␣ and Al K ␣ excitation and a Specs PHOIBOS 150 MCD electron analyzer ͑calibrated according to Ref. 12͒. Subsequently, XES was performed at the ALS using the soft x-ray fluorescence endstation of Beamline 8.0.XPS survey spectra ͑not shown͒ show all expected absorber photoemission lines, Na-related peaks, and only minor spectral contributions of C-and O-co...

show abstract

Section: ͑͒mentioning

confidence: 99%

Nondestructive depth-resolved spectroscopic investigation of the heavily intermixed In2S3/Cu(In,Ga)Se2 interface

Bär

Barreau

Couzinié-Devy

et al. 2010

Applied Physics Letters

Self Cite

View full text Add to dashboard Cite

show abstract

“…Ar þ ion sputtering 6 or wet chemical treatments, 27,28 it is reported that [while stored at room temperature under ultrahigh vacuum (UHV) conditions] Na reappears again at the CIGSe surface within days. 6 3. Na affects the reaction mechanism of absorber formation [29][30][31] and hence the grain size, morphology, and texture of the CIGSe layer.…”

Section: Introductionmentioning

confidence: 99%

“…25,26 After removing Na from the CIGSe surface by means of, e.g. Ar þ ion sputtering 6 or wet chemical treatments, 27,28 it is reported that [while stored at room temperature under ultrahigh vacuum (UHV) conditions] Na reappears again at the CIGSe surface within days. 6 3.…”

Section: Introductionmentioning

confidence: 99%

“…Na (from the soda-lime glass substrate) is reported to diffuse through the Mo back contact layer at temperatures as low as 200 C. 23 2. Na accumulates at the CIGSe/Mo interface, 16,24 the surface (in the surface-near region) of the CIGSe absorber, 6,24 and the grain boundaries. 25,26 After removing Na from the CIGSe surface by means of, e.g.…”

Section: Introductionmentioning

confidence: 99%

“…4 In comparison high-efficiency devices on soda-lime glass substrates are typically obtained using growth temperatures of $550 C. Furthermore, it is well known that in a conventional sodalime glass substrate based CIGSe solar cell structure, Na from the soda-lime glass substrate diffuses into the absorber layer due to the elevated temperature during CIGSe formation. [5][6][7][8] Na incorporation into the CIGSe absorber results in a significant improvement of solar cell efficiency, [9][10][11][12] and so for devices based on alternative (i.e., Na-free) substrates, Na must be added deliberately as part of the solar cell manufacturing process. Na can be incorporated prior to, 13,14 during, 12,15 or after 2,16 CIGSe growth.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

View full text Add to dashboard Cite

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)

show abstract

Process integration issues in thin-film photovoltaics and their impact on future research directions

Sheldon

2000

Prog. Photovolt: Res. Appl.

View full text Add to dashboard Cite

Thin‐film device processing relies heavily on the integration of a variety of materials and a wide array of process steps. These include in some instances, the integration of ‘wet’ (chemical etching) and ‘dry’ (deposition and plasma etching) process steps. As substrates are stepped through the process sequence, there are many surfaces that ultimately become interfaces that can have a dramatic impact on ultimate device performance. However, in thin‐film R&D, these issues are not always carefully considered. This can have severe consequences when adapting an R&D‐developed process into pilot production, and finally, into manufacturing. In this paper, we explore the impact of process integration issues on the microstructure and device performance for three prominent photovoltaic thin‐film technologies (cadmium telluride, copper indium diselenide, and amorphous silicon). We also consider the impact of these concepts on future research directions in thin‐film photovoltaics. Published in 2000 by John Wiley & Sons, Ltd.

show abstract

Na-induced effects on the electronic structure and composition of Cu(In,Ga)Se2 thin-film surfaces

Cited by 90 publications

References 7 publications

Nondestructive depth-resolved spectroscopic investigation of the heavily intermixed In2S3/Cu(In,Ga)Se2 interface

Nondestructive depth-resolved spectroscopic investigation of the heavily intermixed In2S3/Cu(In,Ga)Se2 interface

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

Process integration issues in thin-film photovoltaics and their impact on future research directions

Contact Info

Product

Resources

About