Hostname: page-component-78c5997874-xbtfd Total loading time: 0 Render date: 2024-11-19T22:37:58.519Z Has data issue: false hasContentIssue false
  • English
  • Français

Thermodynamic limitations for alkali metals in Cu(In,Ga)Se2

Published online by Cambridge University Press:  17 October 2017

Dimitrios Hariskos  and
Michael Powalla
Dimitrios Hariskos*
Affiliation:
Center for Solar Energy and Hydrogen Research Baden-Württemberg, Stuttgart 70563, Germany
Michael Powalla
Affiliation:
Center for Solar Energy and Hydrogen Research Baden-Württemberg, Stuttgart 70563, Germany
*
a) Address all correspondence to this author. e-mail: [email protected]
Get access

Abstract

The efficiency of Cu(In,Ga)Se2 (CIGS)-based solar cells could be continuously increased up to 22.6% by employing alkali metal dopants like Na, K, Rb, and Cs. The alkali metals are supplied to the CIGS layer from the glass substrate during deposition, from precursor layers or by a post deposition treatment. The alkali metal distribution in CIGS is not homogenous. Independently of the alkali metals used, their concentration at grain boundaries is much higher than that inside the grains. In this contribution, we discuss thermodynamic limitations for alkali metals in CIGS and show that in higher concentrations they are responsible for secondary phase separation. Applying the concept of immiscibility of phases for alkali metals in CIGS, we suggest how segregation at grain boundaries, formation of clusters in CIGS grains, sporadic formation of microstructures in the CIGS layer (hotspots, nodules), and separation of secondary phases with ordered structures can be interpreted.

Keywords

photovoltaicthin filmsecond phases
Type
Invited Feature Paper
Information
Journal of Materials Research , Volume 32 , Issue 20 , 27 October 2017 , pp. 3789 - 3800
Check for updates
Copyright
Copyright © Materials Research Society 2017 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Footnotes

Contributing Editor: Gary L. Messing

This paper has been selected as an Invited Feature Paper.

References

REFERENCES

Jackson, P., Wuerz, R., Hariskos, D., Lotter, E., Witte, W., and Powalla, M.: Effects of heavy alkali elements in Cu(In,Ga)Se2 solar cells with efficiencies up to 22.6%. Phys. Status Solidi RRL 10, 583–586 (2016).CrossRefGoogle Scholar
Solar Frontier: Press release (2017). Available at: http://www.solar-frontier.com/eng/news/2017/0227_press.html (accessed February 27, 2017).Google Scholar
Solibro: Press release (2017). Available at: http://solibro-solar.com/en/news-downloads/news/ (accessed January, 2017).Google Scholar
Singh, U.P. and Patra, S.P.: Progress in polycrystalline thin-film Cu(In,Ga)Se2 solar cells. Int. J. Photoenergy, 2010, Article ID 468147 (2010). doi: 10.1155/2010/468147.CrossRefGoogle Scholar
Abou-Ras, D., Wagner, S., Stanbery, B.J., Schock, H-W., Scheer, R., Stolt, L., Siebentritt, S., Lincot, D., Eberspacher, C., Kushiya, K., and Tiwari, A.N.: Innovation highway: Breakthrough milestones and key developments in chalcopyrite photovoltaics from a retrospective viewpoint. Thin Solid Films 633, 2–12 (2017).CrossRefGoogle Scholar
Niki, S., Contreras, M., Repins, I., Powalla, M., Kushiya, K., Ishizuka, S., and Matsubara, K.: CIGS absorbers and processes. Prog. Photovoltaics 18, 453–466 (2010).CrossRefGoogle Scholar
Shafarman, W.N., Siebentritt, S., and Stolt, L.: Cu(InGa)Se2 Solar Cells. In Handbook of Photovoltaic Science and Engineering, 2nd ed., Luque, A. and Hegedus, S., eds. (John Wiley & Sons, Chippenham, Wiltshire, U.K., 2011); pp. 546–599.Google Scholar
Kodigala, S.R., ed.: Cu(In1−x Ga x )Se2 and CuIn(Se1−x S x )2 thin film solar cells. In Thin Films and Nanostructures (Book Series), Vol. 35 (Academic Press, U.K., 2010); pp. 2–685.Google Scholar
Scheeer, R. and Schock, H.W.: Chalcogenide Photovoltaics, 1st ed. (WILEY-VCH Verlag & Co. KGaA, Singapore, 2011).CrossRefGoogle Scholar
National Renewable Energy Laboratory NREL. Available at: https://www.nrel.gov/pv/assets/images/efficiency-chart.png (accessed September 12, 2017).Google Scholar
Mickelsen, R.A. and Chen, W.S.: Development of a 9.4% efficient thin-film CuInSe2/CdS solar cell. In Rec. 15th IEEE Photovoltaic Spec. Conf., Kissimmee, Florida, May 12–15 (IEEE, New York, 1981); pp. 800–804.Google Scholar
Klenk, R., Walter, T., Schock, H-W., and Cahen, D.: A model for the successful growth of polycrystalline films of CuInSe2 by multisource physical vacuum evaporation. Adv. Mater. 5, 114–119 (1993).CrossRefGoogle Scholar
Chen, W.S., Stewart, J.M., Stanbery, B.J., Devaney, W.E., and Mickelsen, R.A.: Development of thin film polycrystalline CuIn1−x Ga x Se2 solar cells. In Rec. 19th IEEE Photovoltaic Spec. Conf., New Orleans, Louisiana, May 4–8 (IEEE, New York, 1987); pp. 1445–1447.Google Scholar
Kapur, V.K., Choudary, U.V., and Chu, A.K.P.: Process of forming a compound semiconductive material. US Patent No. 4,581,108, 1986.Google Scholar
Mitchell, K., Eberspacher, C., Ermer, J., and Pier, D.: Single and tandem junction CuInSe2 cell and module technology. In Rec. 20th IEEE Photovoltaic Spec. Conf., Las Vegas, Nevada, September 26–30 (IEEE, New York, 1988); pp. 1384–1389.Google Scholar
Jensen, C.L., Tarrant, D.E., Ermer, J.H., and Pollock, G.A.: The role of Gallium in CuInSe2 solar cells fabricated by a two stage method. In Rec. 23rd IEEE Photovoltaic Spec. Conf., Louisville, Kentucky, May 10-14 (IEEE, New York, 1993); pp. 577–580.Google Scholar
Mitchell, K.W., Eberspacher, C., Ermer, J.H., Pauls, K.L., and Pier, D.N.: CuInSe2 cells and modules. IEEE Trans. Electron Devices 37, 410–417 (1990).CrossRefGoogle Scholar
Hedström, J., Ohlsén, H., Bodegård, M., Kylner, A., Stolt, L., Hariskos, D., Ruckh, M., and Schock, H.W.: ZnO/CdS/Cu(In,Ga)Se2 Thin film solar cells with improved performance. In Rec. 23rd IEEE Photovoltaic Spec. Conf., Louisville Kentucky, May 10–14 (IEEE, New York, 1993); pp. 364–371.Google Scholar
Potter, R.R.: Enhanced photocurrent ZnO/CdS/CuInSe2 solar cells. Sol. Cells 16, 521–527 (1986).CrossRefGoogle Scholar
Kessler, J., Velthaus, K.O., Ruckh, M., Laichinger, R., Schock, H.W., Lincot, D., Ortega, R., and Vedel, J.: Chemical bath deposition of CdS on CuInSe2, etching effects and growth kinetics. In Proc. 6th Int. Photovoltaic Sci. Eng. Conf. (PVSEC-6), New Delhi, India, February 10–14, Das, B.K. and Singh, S.N., eds. (Oxford & Ibh Publishing Co. Pvt. Ltd., New Delhi, 1992); pp. 1005–1010.Google Scholar
Deveney, W.E., Chen, W.S., Stewart, J.M., and Gilette, R.B.: High efficiency CuInSe2 and CuInGaSe2 based cells and materials research. In Final Technical Progress Report for the Contract ZL-8-06031-8, Period 1987–1989 (Boing Electronics High Technology Center, Seattle, Washington, 1990); pp. 17–19.Google Scholar
Ahrenkiel, R.K., Kazmerski, L.L., Matson, R.J., Osterwald, C., Massopust, T.P., Mickelsen, R.A., and Chen, W.S.: Heterojunction formation in (CdZn)S/CulnSe2 ternary solar cells. Appl. Phys. Lett. 43, 658–660 (1983).CrossRefGoogle Scholar
Mickelsen, R.A. and Chen, W.: Polycrystalline thin-film CuInS2 solar cells. In Rec. 16th IEEE Photovoltaic Spec. Conf., San Diego, California, September 27–30 (IEEE, New York, 1982); pp. 781–785.Google Scholar
Goedecke, T., Haalboom, T., and Ernst, F.: Phase equilibria of Cu–In–Se. I. Stable states and nonequilibrium states of the In2Se3–Cu2Se subsystem. Z. Metallkd. 91, 622–634 (2000).Google Scholar
Beilharz, C.: Charakterisierung von aus der Schmelze gezüchteten Kristallen in den Systemen Kupfer–Indium–Selen und Kupfer–Indium–Gallium–Selen für photovoltaische Anwendungen. Ph.D. dissertation, Shaker Verlag, Aachen, 1999.Google Scholar
Stanbery, B.J.: Copper indium selenides and related materials for photovoltaic devices. Crit. Rev. Solid State Mater. Sci. 27, 73–117 (2002).CrossRefGoogle Scholar
Contreras, M.A., Tuttle, J.R., Gabor, A., Tennant, A., Ramanathan, K., Asher, S., Franz, A., Keane, J., Wang, L., Scofield, J., and Noufi, R.: High efficiency Cu(In,Ga)Se2-based solar cells: Processing of novel absorber structures. In Rec. 24th IEEE Photovoltaics Spec. Conf. (1st WCPEC), Waikoloa, Hawaii, December 5–9 (IEEE, New York, 1994); pp. 68–75.Google Scholar
Repins, I., Contreras, M.A., Egaas, B., DeHart, C., Scharf, J., Perkins, C.L., To, B., and Noufi, R.: 19.9%-efficient ZnO/CdS/CuInGaSe2 solar cell with 81.2% fill factor. Prog. Photovoltaics 16, 235–239 (2008).CrossRefGoogle Scholar
Jackson, P., Hariskos, D., Lotter, E., Paetel, S., Wuerz, R., Menner, R., Wischmann, W., and Powalla, M.: New world record efficiency for Cu(In,Ga)Se2 thin-film solar cells beyond 20%. Prog. Photovoltaics 19, 894–897 (2011).CrossRefGoogle Scholar
Tanaka, Y., Akema, N., Morishita, T., Okumura, D., and Kushiya, K.: Improvement of V OC upward of 600 mV/cell with CIGS-based absorber prepared by selenization/sulfurization. In Proc. 17th Eur. Photovoltaic Sol. Energy Conf., Munich, Germany, October 22–26, McNelis, B., Palz, W., Ossenbrink, H.A., and Helm, P., eds. (WIP, Munich, Germany, 2001); pp. 989–994.Google Scholar
Palm, J., Probst, V., and Karg, F.H.: Second generation CIS solar modules. Sol. Energy 77, 757–765 (2004).CrossRefGoogle Scholar
Rudmann, O.D. and Tiwari, A.N.: Verfahren zur Herstellung einer Verbindungshalbleiterschicht mit Alkalizusatz, Patent DE 102 59 258 B4 2006.03.16, December 11, 2002.Google Scholar
Chirilă, A., Reinhard, P., Pianezzi, F., Bloesch, P., Uhl, A.R., Fella, C., Kranz, L., Keller, D., Gretener, C., Hagendorfer, H., Jaeger, D., Erni, R., Nishiwaki, S., Buecheler, S., and Tiwari, A.N.: Potassium-induced surface modification of Cu(In,Ga)Se2 thin films for high-efficiency solar cells. Nat. Mater. 12, 1107–1111 (2013).CrossRefGoogle Scholar
Jackson, P., Hariskos, D., Wuerz, R., Wischmann, W., and Powalla, M.: Compositional investigation of potassium doped Cu(In,Ga)Se2 solar cells with efficiencies up to 20.8%. Phys. Status Solidi RRL 8, 219–222 (2014).CrossRefGoogle Scholar
Lundberg, O., Wallin, E., Gusak, V., Södergren, S., Chen, S., Lotfi, S., Chalvet, F., Malm, U., Kaihovirta, N., Mende, P., Jaschke, G., Kratzert, P., Joel, J., Skupinski, M., Lindberg, P., Jarmar, T., Lundberg, J., Mathiasson, J., and Stolt, L.: Improved CIGS modules by KF post deposition treatment and reduced cell-to-module losses. In Rec. 43rd IEEE Photovoltaic Spec. Conf., Portland, Oregon, June 5–10 (IEEE, New York, 2016); pp. 1293–1296.Google Scholar
Jackson, P., Hariskos, D., Wuerz, R., Kiowski, O., Bauer, A., Friedlmeier, T.M., and Powalla, M.: Properties of Cu(In,Ga)Se2 solar cells with new record efficiencies up to 21.7%. Phys. Status Solidi RRL 9, 28–31 (2015).CrossRefGoogle Scholar
Kamada, R., Yagioka, T., Adachi, S., Handa, A., Tai, K.F., Kato, T., and Sugimoto, H.: New world record Cu(In,Ga)(Se,S)2 thin film solar cell efficiency beyond 22%. In Rec. 43rd IEEE Photovoltaic Spec. Conf. (2016); pp. 1287–1291.Google Scholar
Kato, T.: Cu(In,Ga)(Se,S)2 solar cell research in solar Frontier: Progress and current status. Jpn. J. Appl. Phys. 56, 04CA02 (2017).CrossRefGoogle Scholar
Salomé, P.M.P., Rodriguez-Alvarez, H., and Sadewasser, S.: Incorporation of alkali metals in chalcogenide solar cells. Sol. Energy Mater. Sol. Cells 143, 9–20 (2015).CrossRefGoogle Scholar
Cojocaru-Mirédin, O., Choi, P., Wuerz, R., and Raabe, D.: Atomic-scale distribution of impurities in CuInSe2-based thin-film solar cells. Ultramicroscopy 111, 552–556 (2011).CrossRefGoogle ScholarPubMed
Cadel, E., Barreau, N., Kessler, J., and Pareige, P.: Atom probe study of sodium distribution in polycrystalline Cu(In,Ga)Se2 thin film. Acta Mater. 58, 2634–2637 (2010).CrossRefGoogle Scholar
Vilalta-Clemente, A., Castro, C., Raghuwanshi, M., Duguay, S., Cadel, E., Pareige, P., Jackson, P., Hariskos, D., Wuerz, R., and Witte, W.: Distribution of alkali elements in Cu(In,Ga)Se2 solar cells on a nanometer scale. Presented at the Symp. E, Eur. Mater. Res. Soc. Meet. (EMRS), Strasburg, France, May 22–26, 2017 (EMRS, 2017), Symp. E, No E.III.3. (2017).Google Scholar
Cahen, D. and Noufi, R.: Free energies and enthalpies of possible gas phase and surface reactions for preparation of CuInSe2 . J. Phys. Chem. Solids 53, 991–1005 (1992).CrossRefGoogle Scholar
Guillemoles, J-F., Kronik, L., Cahen, D., Rau, U., Jasenek, A., and Werner Schock, H.: Stability issues of Cu(In,Ga)Se2-based solar cells. J. Phys. Chem. B 104, 4849–4862 (2000).CrossRefGoogle Scholar
Guillemoles, J.F.: Stability of Cu(In,Ga)Se2 solar cells: A thermodynamic approach. Thin Solid Films 361–362, 338–345 (2000).CrossRefGoogle Scholar
Guillemoles, J.F.: The puzzle of Cu(In,Ga)Se2 (CIGS) solar cells stability. Thin Solid Films 403–404, 405–409 (2002).CrossRefGoogle Scholar
Wei, S-H., Zhang, S.B., and Zunger, A.: Effects of Na on the electrical and structural properties of CuInSe2 . J. Appl. Phys. 85, 7214–7218 (1999).CrossRefGoogle Scholar
Pohl, J. and Albe, K.: Thermodynamics and kinetics of the copper vacancy in CuInSe2, CuGaSe2, CuInS2, and CuGaS2 from screened-exchange hybrid density functional theory. J. Appl. Phys. 108, 023509 (2010); J. Appl. Phys. 110, 109905 (2011).CrossRefGoogle Scholar
Persson, C., Zhao, Y-J., Lany, S., and Zunger, A.: n-Type doping of CuInSe2 and CuGaSe2 . Phys. Rev. B 72, 035211 (2005).CrossRefGoogle Scholar
Malitckaya, M., Komsa, H-P., Havu, V., and Puska, M.J.: First-principles modeling of point defects and complexes in thin-film solar-cell absorber CuInSe2 . Adv. Electron. Mater. 3, 1600353 (2017).CrossRefGoogle Scholar
Rudmann, D.: Effects of sodium on growth and properties of Cu(In,Ga)Se2 thin films and solar cells. Ph.D. dissertation, Swiss Federal Institute of Technology, Zürich, 2004.Google Scholar
Oikkonen, L.E., Ganchenkova, M.G., Seitsonen, A.P., and Nieminen, R.M.: Effect of sodium incorporation into CuInSe2 from first principles. J. Appl. Phys. 114, 083503 (2013).CrossRefGoogle Scholar
Alling, B., Högberg, H., Armiento, R., Rosen, J., and Hultman, L.: A theoretical investigation of mixing thermodynamics, age hardening potential, and electronic structure of ternary M11−x M2 x B2 alloys with A|B2 type structure. Sci. Rep. 5, 09888 (2015).CrossRefGoogle ScholarPubMed
Provatas, N. and Elder, K.: Phase-Field Methods in Material Science and Engineering (Wiley VCH, Singapore, 2010).CrossRefGoogle Scholar
Balluffi, R.W., Allen, S.M., and Carter, W.C.: Kinetics of Materials (John Wiley & Sons, Inc., Hoboken, NJ, USA, 2005).CrossRefGoogle Scholar
Schaftenaar, H.P.C.: Theory and Examples of Spinodal Decomposition in a Variety of Materials (Utrecht University, The Netherlands, 2008).Google Scholar
Porter, D.A., Easterling, K.E., and Sherif, M.Y.: Phase Transformations in Metals and Alloys, 3rd ed. (CRC Press, Boca Raton FL, USA, 2009).Google Scholar
Holder, A.M., Siol, S., Ndione, P.F., Peng, H., Deml, A.M., Matthews, B.E., Schelhas, L.T., Toney, M.F., Gordon, R.G., Tumas, W., Perkins, J.D., Ginley, D.S., Gorman, B.P., Tate, J., Zakutayev, A., and Lany, S.: Novel phase diagram behavior and materials design in heterostructural semiconductor alloys. Sci. Adv. 3, e1700270 (2017).CrossRefGoogle ScholarPubMed
Chan, J.W. and Charles, R.J.: The initial stages of phase separation in glasses. Phys. Chem. Glasses 6, 181–191 (1965).Google Scholar
Sangster, J. and Pelton, A.D.: The Na–Se (sodium–selenium) system. J. Phase Equilib. 18, 185–189 (1997).CrossRefGoogle Scholar
Sangster, J. and Pelton, A.D.: The K–Se (potassium–selenium) system. J. Phase Equilib. 18, 177–180 (1997).CrossRefGoogle Scholar
Sangster, J. and Pelton, A.D.: The Rb–Se (rubidium–selenium) system. J. Phase Equilib. 18, 190–193 (1997).CrossRefGoogle Scholar
Sangster, J. and Pelton, A.D.: The Cs–Se (cesium–selenium) system. J. Phase Equilib. 18, 173–176 (1997).CrossRefGoogle Scholar
Hoppe, R., Lidecke, W., and Frorath, F-C.: Zur Kenntnis von NaInS2 und NaInSe2 . Z. Anorg. Allg. Chem. 309, 49–54 (1961).CrossRefGoogle Scholar
Schlosser, M., Reiner, C., Deiseroth, H-J., and Kienle, L.: K2In12Se19, a complex new structure type based on icosahedral units of Se2− . Eur. J. Inorg. Chem. 2001, 2241–2247 (2001).3.0.CO;2-E>CrossRefGoogle Scholar
Peterson, G.E. and Bridenbaugh, P.M.: Nuclear quadrupole coupling constants and charge distributions in ionic crystals of the NaFeO2 type. J. Chem. Phys. 51, 2610 (1969).CrossRefGoogle Scholar
Krebs, B.: Thio- und Selenoverbindungen von Hauptgruppenelementen–neue anorganische Oligomere und Polymere. Angew. Chem. 95, 113–134 (1983).CrossRefGoogle Scholar
Huanga, F.Q., Denga, B., Ellis, D.E., and Ibers, J.A.: Preparation, structures, and band gaps of RbInS2 and RbInSe2 . J. Solid State Chem. 178, 2128–2132 (2005).CrossRefGoogle Scholar
Do, J. and Kanatzidis, M.G.: The one-dimensional polyselenide compound CsGaSe3 . Z. Anorg. Allg. Chem. 629, 621–624 (2003).CrossRefGoogle Scholar
Friedrich, D., Schlosser, M., and Pfitzner, A.: Synthesis and structural characterization of Cs2Ga2Se5 . Z. Anorg. Allg. Chem. 640(5), 826–829 (2014).CrossRefGoogle Scholar
Zellner, M.B., Birkmire, R.W., Eser, E., Shafarman, W.N., and Chen, J.G.: Determination of activation barriers for the diffusion of sodium through CIGS thin-film solar cells. Prog. Photovoltaics 11, 543–548 (2003).CrossRefGoogle Scholar
Yoon, J-H., Seong, T-Y., and Jeong, J.: Effect of a Mo back contact on Na diffusion in CIGS thin film solar cells. Prog. Photovoltaics 21, 58–63 (2013).CrossRefGoogle Scholar
Laemmle, A., Wuerz, R., Schwarz, T., Cojocaru-Mirédin, O., Choi, P.P., and Powalla, M.: Investigation of the diffusion behavior of sodium in Cu(In,Ga)Se2 layers. J. Appl. Phys. 115, 154501 (2014).CrossRefGoogle Scholar
Abou-Ras, D., Schmidt, S.S., Caballero, R., Unold, T., Schock, H-W., Koch, C.T., Schaffer, B., Schaffer, M., Choi, P-P., and Cojocaru-Mirédin, O.: Confined and chemically flexible grain boundaries in polycrystalline compound semiconductors. Adv. Energy Mater. 2, 992–998 (2012).CrossRefGoogle Scholar
Choi, P.P., Cojocaru-Mirédin, O., Wuerz, R., and Raabe, D.: Comparative atom probe study of Cu(In,Ga)Se2 thin-film solar cells deposited on soda-slime glass and mild steel substrates. J. Appl. Phys. 110, 124513 (2011).CrossRefGoogle Scholar
Contreras, M.A., Egaas, B., Dippo, P., Webb, J., Granata, J., Ramanathan, K., Asher, S., Swartzlander, A., and Noufi, R.: On the role of Na and modifications to Cu(In,Ga)Se2 absorber materials using thin MF (M = Na, K, Cs) precursor layers. In Rec. 26th IEEE Photovoltaic Spec. Conf., Anaheim, California, September 29-October 3 (IEEE, New York, 1997); pp. 359–362.Google Scholar
Database of the International Centre for Diffraction Data, JCPDS 01-074-0136.Google Scholar
Lin, Y.C., Shi, Z.H., Shen, C.H., and Chen, Y.L.: Na-doped Mo target sputtering for CIGS thin film solar cells on stainless steel substrate. Int. J. Appl. Phys. Math. 3, 157–160 (2013).CrossRefGoogle Scholar
Lee, J.W., Kaczynski, R., Van Alsburg, J., Sang, B., Schoop, U., and Britt, J.: Effect of three-stage growth modification on a CIGS microstructure. IEEE J. Photovolt. 6, 1645–1649 (2016).CrossRefGoogle Scholar
Nadenau, V., Lippold, G., Rau, U., and Schock, H.W.: Sodium induced secondary phase segregations in CuGaSe2 thin films. J. Cryst. Growth 233, 13–21 (2001).CrossRefGoogle Scholar
Balboul, M.R., Turcu, M., Kötschau, I.M., Rau, U, and Schock, H.W.: Sodium induced phase segregations in CuGaSe2 and CuInSe2 thin films. In Proc. 17th Eur. Photovoltaic Sol. Energy Conf., Munich Germany, October 22–26, McNelis, B., Palz, W., Ossenbrink, H.A., and Helm, P., eds. (WIP, Munich, Germany, 2001); pp. 1015–1018.Google Scholar
Song, X., Caballero, R., Félix, R., Gerlach, D., Kaufmann, C.A., Schock, H-W., Wilks, R.G., and Bär, M.: Na incorporation into Cu(In,Ga)Se2 thin-film solar cell absorbers deposited on polyimide: Impact on the chemical and electronic surface structure. J. Appl. Phys. 111, 034903 (2012).CrossRefGoogle Scholar
Schmid, D., Ruckh, M., Grunwald, F., and Schock, H.W.: Chalcopyrite defect chalcopyrite heterojunctions on the basis of CulnSe2 . J. Appl. Phys. 73, 2902 (1993).CrossRefGoogle Scholar
Contreras, M.A. and Noufi, R.: Chalcopyrite Cu(In,Ga)Se2 and defect-chalcopyrite Cu(In,Ga)3Se5 materials in photovoltaic P–N junctions. J. Cryst. Growth 174, 283–288 (1997).CrossRefGoogle Scholar
Mönig, H., Fischer, C-H., Grimm, A., Johnson, B., Kaufmann, C.A., and Caballero, R.: Surface Cu-depletion of Cu(In,Ga)Se2 thin films: Further experimental evidence for a defect-induced surface reconstruction. J. Appl. Phys. 107, 113540 (2010).CrossRefGoogle Scholar
Reinhard, P., Bissig, B., Pianezzi, F., Hagendorfer, H., Sozzi, G., Menozzi, R., Gretener, C., Nishiwaki, S., Buecheler, S., and Tiwari, A.N.: Alkali-templated surface nanopatterning of chalcogenide thin films: A novel approach toward solar cells with enhanced efficiency. Nano Lett. 15, 3334–3340 (2015).CrossRefGoogle ScholarPubMed
Handick, E., Reinhard, P., Wilks, R.G., Pianezzi, F., Félix, R., Gorgoi, M., Kunze, T., Buecheler, S., Tiwari, A.N., and Bär, M.: NaF/KF post-deposition treatments and their influence on the structure of Cu(In,Ga)Se2 absorber surfaces. In Rec. 43rd IEEE Photovoltaic Spec. Conf., Portland, Oregon, June 5–6 (IEEE, New York, 2016); pp. 017–021.Google Scholar
Malitckaya, M., Komsa, H-P., Havu, V., and Puska, M.: Effect of alkali metal atom doping on CuInSe2-based solar cell absorber. J. Phys. Chem. C 121, 15516–15528 (2017).CrossRefGoogle Scholar
Couzinie-Devy, F., Cadel, E., Barreau, N., Arzel, L., and Pareige, P.: Atom probe study of Cu-poor to Cu-rich transition during Cu(In,Ga)Se2 growth. Appl. Phys. Lett. 99, 232108 (2011).CrossRefGoogle Scholar
Hanna, G.: Determination and influence of Na supply and Se flux during growth of Cu(In,Ga)Se2 thin films. Ph.D. dissertation, University of Stuttgart, Germany, 2004.Google Scholar
Colombara, D., Berner, U., Ciccioli, A., Malaquias, J.C., Bertram, T., Crossay, A., Schöneich, M., Meadows, H.J., Regesch, D., Delsante, S., Gigli, G., Valle, N., Guillot, J., Adib, B.E., Grysan, P., and Dale, P.J.: Deliberate and accidental gas-phase alkali doping of chalcogenide semiconductors: Cu(In,Ga)Se2 . Sci. Rep. 7, 43266 (2017).CrossRefGoogle Scholar
Yuan, Z.K., Chen, S., Xie, Y., Park, J.S., Xiang, H., Gong, X.G., and Wei, S.H.: Na-diffusion enhanced p-type conductivity in Cu(In,Ga)Se2: A new mechanism for efficient doping in semiconductors. Adv. Energy Mater. 6, 1601191 (2016).CrossRefGoogle Scholar