Cu(In,Ga)Se2 (CIGSe) semiconductor compound showing record photovoltaic conversion efficiencies near 20% has become a leading material for thin film solar cell applications. Investigations in AIBIIISe2 materials have been focused on device performance in order to enhance solar cell efficiency by maximizing the open-circuit voltage and short-circuit current, whereas controlling the electrical properties of the absorber material such as mobility, crystal defect formation, and charge carrier concentration are very important issues to achieve highly efficient CIGSe-base solar cells. In the processing of CIGSe thin film deposition, the ratio of Cu:In:Ga changes undesirably and it influences the electrical properties of the absorber layer and the solar cell performance consequently. Without accurate control in composition, the induced defects may be attributed to many factors and it would be so complex and filled with assumptions to vindicate an explanation. However, investigations on electrical properties of CIGSe material are feasible by systematic study of its bulk form with the favorable composition design.
In the first part of this work, the Cu-poor, Cu-rich, and In-rich CIGSe bulk materials have been sintered in order to study the roles of Cu and In vacancies and antisite defect formation in electrical properties and microstructure of CIGSe material. The reactive liquid-phase sintering technique has been used to fabricate CIGSe dense bulks at a low temperature in order to maintain the atomic composition of the compounds very close to our favored design. Sintering of CIGSe bulk material has been carried out in the presence of Sb2S3 and Te sintering aids to assist densification at 650 ˚C. Electrical properties of the CIGSe bulk materials showed that carrier concentration and mobility enhanced with increasing Cu content. The larger grains of CIGSe material have been achieved with high Cu content. The maximum amount of mobility was 5.38 cm2/V.s for the Cu-rich sample with Cu1.1(In0.7Ga0.3)Se2 formula. The change in carrier concentration and transition of conductivity type from p-type to n-type material in In-rich sample confirmed our explanation about the In and Cu vacancy and interstitial defects. We could achieve CIGSe material with a lower carrier concentration by introducing the excess amount of In to A site of AIBIIISeVI2 structure.
In the second part of this work, some elements like Sn, Mg, and Al have been doped into CIGSe bulks to investigate the influence of these dopants on electrical properties and microstructure of CIGSe material. Increasing the Sn-dopant content led to the increase in hole concentration but at a doping content of 15.6% the conductivity type of CIGSe transformed from p-type to n-type regardless of the sintering temperature. More Sn doping led to larger CIGSe grains and lattice shrinkage. Carrier mobility above 12 cm2/V责s could be achieved for the n-type Sn-doped CIGSe with a higher Cu content. The favored low concentration of holes in the order of 1016 cm–3 and mobility above 4 cm2/V责s was achieved for CIGSe material doped with 10% of Mg. The n-type Cu0.7[(In0.6Al0.1)Ga0.3]Se2 material was obtained in Al-doped CIGSe bulks and the p-type one was achieved at higher Cu contents. The data of lattice parameters have been used to confirm the change in electrical properties of CIGSe bulk materials and explanation of defect formation mechanisms.

Cu(In,Ga)Se2 (CIGSe) semiconductor compound showing record photovoltaic conversion efficiencies near 20% has become a leading material for thin film solar cell applications. Investigations in AIBIIISe2 materials have been focused on device performance in order to enhance solar cell efficiency by maximizing the open-circuit voltage and short-circuit current, whereas controlling the electrical properties of the absorber material such as mobility, crystal defect formation, and charge carrier concentration are very important issues to achieve highly efficient CIGSe-base solar cells. In the processing of CIGSe thin film deposition, the ratio of Cu:In:Ga changes undesirably and it influences the electrical properties of the absorber layer and the solar cell performance consequently. Without accurate control in composition, the induced defects may be attributed to many factors and it would be so complex and filled with assumptions to vindicate an explanation. However, investigations on electrical properties of CIGSe material are feasible by systematic study of its bulk form with the favorable composition design.
In the first part of this work, the Cu-poor, Cu-rich, and In-rich CIGSe bulk materials have been sintered in order to study the roles of Cu and In vacancies and antisite defect formation in electrical properties and microstructure of CIGSe material. The reactive liquid-phase sintering technique has been used to fabricate CIGSe dense bulks at a low temperature in order to maintain the atomic composition of the compounds very close to our favored design. Sintering of CIGSe bulk material has been carried out in the presence of Sb2S3 and Te sintering aids to assist densification at 650 ˚C. Electrical properties of the CIGSe bulk materials showed that carrier concentration and mobility enhanced with increasing Cu content. The larger grains of CIGSe material have been achieved with high Cu content. The maximum amount of mobility was 5.38 cm2/V.s for the Cu-rich sample with Cu1.1(In0.7Ga0.3)Se2 formula. The change in carrier concentration and transition of conductivity type from p-type to n-type material in In-rich sample confirmed our explanation about the In and Cu vacancy and interstitial defects. We could achieve CIGSe material with a lower carrier concentration by introducing the excess amount of In to A site of AIBIIISeVI2 structure.
In the second part of this work, some elements like Sn, Mg, and Al have been doped into CIGSe bulks to investigate the influence of these dopants on electrical properties and microstructure of CIGSe material. Increasing the Sn-dopant content led to the increase in hole concentration but at a doping content of 15.6% the conductivity type of CIGSe transformed from p-type to n-type regardless of the sintering temperature. More Sn doping led to larger CIGSe grains and lattice shrinkage. Carrier mobility above 12 cm2/V责s could be achieved for the n-type Sn-doped CIGSe with a higher Cu content. The favored low concentration of holes in the order of 1016 cm–3 and mobility above 4 cm2/V责s was achieved for CIGSe material doped with 10% of Mg. The n-type Cu0.7[(In0.6Al0.1)Ga0.3]Se2 material was obtained in Al-doped CIGSe bulks and the p-type one was achieved at higher Cu contents. The data of lattice parameters have been used to confirm the change in electrical properties of CIGSe bulk materials and explanation of defect formation mechanisms.

[1] Johan Wennerberg: Design and Stability of Cu(In,Ga)Se2 Based Solar Cell Modules, Uppsala Universitet Examensarbete (2002).
[2] Available in: http://www.globalwarmingart.com/wiki/Image:Solar_Spectrum_png
[3] D.B. Mitzi, O.Gunawan, T.K. Todorov, K. Wang, S. Guha, “The path towards a high-performance solution-processed kesterite solar cell”, Sol. Energy Mater. Sol. Cells 95 (2011) 1421.
[4] M. Schofthaler, U. Rau, W. Fussel, J.H.Werner, “Optimization of the back contact geometry for high efficiency solar cells”, Proc. 23rd Int. IEEE Photovoltaic Specialists Conf. (1993) 315.
[5] R. Brendel: Thin Film Crystalline Silicon Solar Cells Physics and Technology, Wiley-VCH GmbH & Co. (2003).
[6] S.R. Kodigala: Cu(InxGa1–x)Se2 Based Thin Film Solar cells, Academic Press (2010).
[7] K. Kakishita, K. Aihara, T. Soda, “Zn3P2 photovoltaic film growth for Zn3P2/ZnSe solar cell”, Sol. Energy Mater. Sol. Cell 35 (1994) 333.
[8] T. Pisarkiewicz, K. Zakrzewska, E. Leja, “Preparation, electrical properties and optical characterization of Cd2SnO4 and CdIn2O4 thin films as transparent and conductive coatings”, Thin Solid Films 153 (1987) 479.
[9] R.H. Bube, A.L. Fahrenbruch: Fundamentals of Solar Cells, Academic Press, New York (1983).
[10] J.L. Shay, J.H. Wernick: Ternary Chalcopyrite Semiconductors: Growth, Electronic Properties and Applications, Pergamon Press, New York (1975).
[11] S.K. Chang, H.L. Park, H.K. Kim, J.S. Hwang, C.H. Chung, W.T. Kim, “Co2+ in CuGa1−xAlxSe2 and valence band offset in CuGa1−xAlxSe2/CuGaSe2”, Phys Stat. Solidi (B) 158(2) (1990) K115.
[12] L. Roa, C. Rincon, J. Gonzalez, M. Quintero, “Analysis of direct exciton transitions in CuGa(SxSe1-x)2 alloys”, J. Phys. Chem. Solids 51 (1990) 551.
[13] M. Robbins, V.G. Lambrecht, “Preparation and some properties of materials in systems of the type MIMIIIS2-MIMIIISe2 where MI=Cu, Ag and MIII=Al, Ga, In”, Master. Res. Bull. 8 (1973) 703.
[14] H. Neff, P. Lange, M.L. Fearheiley, K.J. Backmann, “Optical and electrochemical properties of CuInSe2 and CuInS2/CuInSe2 alloys”, Appl. Phys. Lett. 47 (1985) 1089.
[15] B.R. Pamplin, R.S. Feigelson, “Spray pyrolysis of CuInSe2 and related ternary semiconducting compounds”, Thin Solid Films 60 (1979) 141.
[16] J.J. Scragg: Copper Zinc Tin Sulfide Thin Films for Photovoltaics, Springer-Verlag Berlin Heidelberg (2011).
[17] K.J. Bachmane, E. Buchler, J.L. Shay, S. Wagner, “Polycrystalline thin‐film InP/CdS solar cell”, Appl. Phys. Lett., 29 (1976) 121.
[18] R.A. Joshi, V.S. Taur, A.V. Ghule, R. Sharma, “Stoichiometry controlled conversion efficiency in nanostructured heterojunction solar cell of CdS/CuInSxSe2-x grown by chemical ion exchange method at room temperature”, Solar Energy 85 (2011) 1316.
[19] D. Cahen, R. Noufi, “Defect chemical explanation for the effect of air anneal on CdS/CuInSe2 solar cell performance”, Appl. Phys. Lett. 54(6) (1989) 558.
[20] D.C. Reynolds, G. Leies, L.L. Antes, R.E. Marburger, “Photovoltaic effect in cadmium sulfide”, Phys. Rev. 96 (1954) 533.
[21] M.A. Green, K. Emery, Y. Hishikawa, W. Warta, E.D. Dunlop, “Solar cell efficiency tables (version 39)”, Prog. Photovolt, Res. Appl. 20 (2012) 12.
[22] S. Siebentritt, U. Rau (edit.): Wide-gap Chalcopyrites, Springer, Berlin (2006).
[23] M.A. Green, “Estimates of Te and In prices from direct mining of known ores”, Prog. Photovoltaics Res. Appl. 17(5) (2009) 347.
[24] T.M. Razykov, C.S. Ferekides, D. Morel, E. Stefanakos, H.S. Ullal, H.M. Upadhyaya, “Solar photovoltaic electricity: Current status and future prospects”, Solar Energy 85 (2011) 1580.
[25] T. Tiedje, E. Yablonovitsch, G.D. Cody, B.G. Brooks, “Limiting efficiency of silicon solar cells”, IEEE Trans. electron devices 31(5) (1984) 711.
[26] W.Shockley, H.J. Queisser: “Detailed balance limit of efficiency of p-n junction solar cells”, J. Appl. Phys. 32(3) (1961) 510.
[27] S.H. Wei, A. Zunger: “Band offsets and optical bowings of chalcopyrites and Zn-based II-VI alloys”, J. Appl. Phys. 78(6) (1995) 3846.
[28] K. Ito, T. Nakazawa, “Electrical and optical properties of stannite type quaternary semiconductor thin-films”, Jpn. J. Appl. Phys. 27(11) (1988) 2094.
[29] S. Chen, X.G. Gong, A. Walsh, S.H. Wei, “Crystal and electronic band structure of Cu2ZnSnX4 (X = S, Se) photovoltaic absorbers: First principles in-sights”, Appl. Phys. Lett. 94 (2009) 041903.
[30] J. Engman: Experimental Study of Cu2ZnSn(Se,S)4 Thin Films for Solar Cell Applications, Uppsala Universitet Examensarbete (2011).
[31] T. Kirchartz, U.R. Daniel, A. Ras (edit.): Advanced Characterization Techniques for Thin Film Solar Cells, Wiley-VCH Verlag GmbH & Co. KGaA (2011).
[32] F. Hergert, S. Jost, R. Hock, M. Purwins, J. Palm, “Formation reactions of chalcopyrite compounds and the role of sodium doping”, Thin Solid Films 515 (2007) 5843.
[33] J. Palm, V. Probst, F.H. Karg, “Second generation CIS solar modules”, Solar Energy 77 (2004) 757.
[34] K. Sakurai, R. Hunger, N. Tsuchimochi, T. Baba, K. Matsubara, P. Fons, A. Yamada, T. Kojima, T. Deguchi, H. Nakanishi, S. Niki, “Properties of CuInGaSe2 solar cells based upon an improved three-stage process”, Thin Solid Films 431- 432 (2003) 6.
[35] I. Repins, M.A. Contreras, B. Egaas, C. DeHart, J. Scharf, C.L. Perkins, B. To, R. Noufi, “19.9% efficient ZnO/CdS/CuInGaSe2 solar cell with 81.2% fill factor”, Prog. Photovolt: Res. Appl. 16 (2008) 235.
[36] P. Jackson, D. Hariskos, E. Lotter, S. Paetel, R. Wuerz, R. Menner, W. Wischmann, M. Powalla, “New world record efficiency for Cu(In,Ga)Se2 thin film solar cells beyond 20%”, Prog. Photovolt: Res. Appl. 19 (2011) 894.
[37] V. Probst, W. Stetter, W. Riedl, H. Vogt, M. Wendl, H. Calwer, S. Zweigart, K.D. Ufert, B. Freienstein, H. Cerva, F.H. Karg, “Rapid CIS-process for high efficiency PV-modules: development towards large area processing”, Thin Solid Films 387 (2001) 262.
[38] Y. Goushi, H. Hakuma, K. Tabuchi, Sh. Kijima, K. Kushiya, “Fabrication of pentanary Cu(InGa)(SeS)2 absorbers by selenization and sulfurization”, Sol. Energy Mater. Sol. Cells 93 (2009) 1318.
[39] Y. Lai, F. Liu, Z. Zhang, J. Liu, Y. Li, S. Kuang, J. Li, Y. Liu, “Cyclic voltammetry study of electrodeposition of Cu(In,Ga)Se2 thin films”, Electrochim. Acta 54(11) (2009) 3004.
[40] M.E. Calixto, P.J. Sebastian, “Depth profile analysis of CuInSe2 (CIS) thin films grown by the electrodeposition technique”, Sol. Energy Mat. Sol. Cells 63(4) (2000) 335.
[41] A.M. Hermann, C. Gonzalez, P.A. Ramakrishnan, D. Balzar, N. Popa, P. Rice, C.H. Marshall, J.N. Hilfiker, T. Tiwald, P.J. Sebastian, M.E. Calixto, R.N. Bhattacharya, “Fundamental studies on large area Cu(In,Ga)Se2 films for high efficiency solar cells”, Sol. Energy Mat. Sol. Cells 70(3) (2001) 345.
[42] M. Ganchev, J. Kois, M. Kaelin, S. Bereznev, E. Tzvetkova, O. Volobujeva, N. Stratieva, A. Tiwari, “Preparation of Cu(In,Ga)Se2 layers by selenization of electrodeposited Cu–In–Ga precursors”, Thin Solid Films 511- 512 (2006) 325.
[43] F. Kang, J. Ao, G. Sun, Q. He, Y. Sun, “Properties of CuInxGa1-xSe2 thin films grown from electrodeposited precursors with different levels of selenium content”, Current Applied Physics 10(3) (2010) 886.
[44] S. Yoon, T. Yoon, K.S. Lee, S. Yoon, J.M. Ha, S. Choe, “Nanoparticle-based approach for the formation of CIS solar cells”, Sol. Energy Mat. Sol. Cells 93(6-7) (2009) 783.
[45] W. Wang, Y.W. Su, C.H. Chang, “Inkjet printed chalcopyrite CuInxGa1-xSe2 thin film solar cells”, Sol. Energy Mat. Sol. Cells 95 (2011) 2616.
[46] C.J. Hibberd, E. Chassaing, W. Liu, D.B. Mitzi, D. Lincot, A.N. Tiwari, “Non-vacuum methods for formation of Cu(In,Ga)(Se,S)2 thin film photovoltaic absorbers”, Prog. Photovolt: Res. Appl. 18 (2010) 434.
[47] T.K. Todorov, O. Gunawan, T. Gokmen, D.B. Mitzi, “Solution-processed Cu(In,Ga) (S,Se)2 absorber yielding a 15.2% efficient solar cell”, Prog. Photovolt: Res. Appl. 21 (2012) 82.
[48] R.M. German: Liquid Phase Sintering, Plenum press, New York (1985).
[49] M. Barsoum: Fundamentals of Ceramics, McGraw-Hill, New York (1997).
[50] T.A. Ring: Fundamentals of Ceramic Powder processing and Synthesis, Academic press, New York (1996).
[51] W.G. Fahrenholtz: Sintering, Uni. of Missouri, lab. Report (2004).
[52] S.B. Zhang, S.H.Wei, A. Zunger, H.K. Yoshida, “Defect physics of the CuInSe2 chalcopyrite semiconductor”, Phys. Rev. B 57 (1998) 9642.
[53] H. Moller, “Structure and defect chemistry of grain boundaries in CuInSe2”, Solar Cells 31(1) (1991) 77.
[54] M. Igalson, H.W. Schock, “The metastable changes of the trap spectra of CuInSe2 based photovoltaic devices”, J. Appl. Phys. 80 (1996) 5765.
[55] T. Walter, R. Herberholz, C. Muller, H.W. Schock, “Determination of defect distri-butions from admittance measurements and application to Cu(In,Ga)Se2 based het-erojunctions”, J. Appl. Phys. 80 (1996) 4411.
[56] R. Herberholz, V. Nadenau, U. Ruhle, C. Koble, H.W. Schock, B. Dimmler, “Prospects of wide-gap chalcopyrites for thin film photovoltaic modules”, Sol. Energy Mater. Sol. Cells 49 (1997) 227.
[57] U. Rau, M. Schmidt, A. Jasenek, G. Hanna, H.W. Schock, “Electrical characterization of Cu(In,Ga)Se2 thin film solar cells and the role of defects for the device performance”, Sol. Energy Mater. Sol. Cells 67 (2001) 137.
[58] M. Turcu, I.M. Kotschau, U. Rau, “Composition dependence of defect energies and band alignments in the Cu(In1-xGax)(Se1-ySy)2 alloy system”, J. Appl. Phys. 91(2002) 1391.
[59] M. Caldas, A. Fazzio, A. Zunger, “A universal trend in the binding energies of deep impurities in semiconductors”, Appl. Phys. Lett. 45 (1984) 67.
[60] J.M. Langer, H. Heinrich, “Deep-level impurities: a possible guide to prediction of band-edge discontinuities in semiconductor heterojunctions”, Phys. Rev. Lett. 55 (1985) 1414.
[61] J.T. Heath, J.D. Cohen, W.N. Shafarman, D.X. Liao, A.A. Rockett, “Effect of Ga content on defect states in CuIn1-xGaxSe2 photovoltaic devices”, Appl. Phys. Lett. 80 (2002) 4540.
[62] M. Igalson, A. Urbaniak, “Defect states in the CIGS solar cells by photo-capacitance and deep level optical spectroscopy”, Bulletin of The Polish Academy of Sciences 53(2) (2005) 157.
[63] K. Yoshino, H. Yokoyama, K. Maeda, T. Ikari, “Crystal growth and photo-luminescence of CuInxGa1-xSe2 alloys”, J. Cryst. Growth 211 (2000) 476.
[64] C. Rincon, S.M. Wasim, G. Marin, “Effect of ordered arrays of native defects on the crystal structure of In- and Ga-rich Cu-ternaries”, Appl. Phys. Lett. 83 (2003) 1328.
[65] R. Noufi, R. Axton, C. Herrington, S.K. Deb, “Electronic properties versus composition of thin films of CulnSe2”, Appl. Phys. Lett. 45 (6) (1984) 668.
[66] A.J. Nelson, A.B. Swartzlander, J.R. Tuttle, R. Noufi, R. Patel, H. Hochst, “Photo-emission investigation of the electronic structure at polycrystalline CuInSe2 thin‐film interfaces”, J. Appl. Phys. 74 (9) (1993) 5757.
[67] D. Schmid, M. Ruckh, F. Grunwald, H.W. Schock, “Chalcopyrite/defect chalcopyrite hetero-junctions on the basis of CuInSe2”, J. Appl. Phys. 73(6) (1993) 2902.
[68] T. Sugiyama, S. Chaisitsak, A. Yamada, M. Konagai, Y. Kudriavtsev, A. Godines, A. Villegas, R. Asomoza, “ Formation of p-n homojunction in Cu(In,Ga)Se2 thin film solar cells by Zn doping”, Jpn. J. Appl. Phys. 39 (2000) 4816.
[69] S. Nishiwaki, T. Satoh, Y. Hashimoto, S.I. Shimakawa, S. Hayashi, T. Negami, T. Wada, “Preparation of Zn doped Cu(In,Ga)Se2 thin films by physical vapor deposition for solar cells”, Sol. Energy Mater. Sol. Cells 77(4) (2003) 359.
[70] A. Rockett, D. Liao, J.T. Heath, J.D. Cohen, Y.M. Strzhemechny, L.J. Brillson, K.Ramanathan , W.N. Shafarman, “Near-surface defect distributions in Cu(In,Ga) Se2”, Thin Solid Films 431-432 (2003) 301.
[71] J.J. Loferski, “Theoretical considerations governing the choice of the optimum semiconductor for photovoltaic solar energy conversion”, J. Appl. Phys. 27 (1956) 777.
[72] P.T. Erslev, J.W. Lee, G.M. Hanket, W.N. Shafarman, J. D. Cohen, “The electronic structure of Cu(In1-xGax)Se2 alloyed with silver”, Thin Solid Films 519 (2011) 7296.
[73] S. Ameen, M.S. Akhtar, H.K. Seo, Y.S. Kim, H.S. Shin, “Influence of Sn doping on ZnO nanostructures from nanoparticles to spindle shape and their photo-electrochemical properties for dye-sensitized solar cells”, Chem. Eng. J. 187 (2012) 351.
[74] J.J. Robbins, C.A. Wolden, “High mobility oxides: Engineered structures to overcome intrinsic performance limitations of transparent conducting oxides”, Appl. Phys. Lett. 83 (2003) 3933.
[75] D.J. Cohen, S.A. Barnett, “Predicted electrical properties of modulation-doped ZnO-based transparent conducting oxides”, J. Appl. Phys. 98 (2005) 053705.
[76] T. Koida, H. Fujiwara, M. Kondo, “Structural and electrical properties of hydrogen-doped In2O3 films fabricated by solid-phase crystallization”, J. Non-Cryst. Solids 354 (2008) 2805.
[77] C.V. Thompson, “Grain growth in thin films”, Annu. Rev. Mater. Sci. 20 (1990) 245.
[78] T. Schlenker, M.L. Valero, H.W. Schock, J.H. Werner, “Grain growth studies of thin Cu(In,Ga)Se2 films”, J. Cryst. Growth 264(1-3) (2004) 178.
[79] A. Rockett, “The effect of Na in polycrystalline and epitaxial single-crystal CuIn1-xGax Se2”, Thin Solid Films 480-481 (2005) 2.
[80] Z.Q. Li, Q.Q. Liu, J.J. Li, Z. Sun, Y.W. Chen, Z. Yang, S.M. Huang, “Growth of Zn doped Cu(In,Ga)Se2 thin films by rf-sputtering for solar cell applications”, Solid-State Electron. 68 (2012) 80.
[81] W.N. Shafarman, J. Zhu, “Effect of substrate temperature and deposition profile on evaporated Cu(ln,Ga)Se2 films and devices”, Thin Solid Films 361-362 (2000) 473.
[82] M.E. Beck, T. Weiss, D. Fischer, S. Fiechter, A.J. Waldau, M.C. Lux-Steiner, “Structural analysis of Cu1-xAgxGaSe2 bulk materials and thin films”, Thin Solid Films 361-362 (2000) 130.
[83] G. Masetti, S. Solmi, “Relationship between carrier mobility and electron concentration in silicon heavily doped with phosphorus”, Solid-State and Electron Devices, IEE Proc. 3(3) (1979) 65.
[84] G. Masetti, M. Severi, S. Solmi, “Modeling of carrier mobility against carrier concen-tration in arsenic, phosphorus, and boron-doped silicon”, IEEE Trans. Electron Devices 30(7) (1983) 764.
[85] A.J. Leenheer, J.D. Perkins, M.V. Hest, J.J. Berry, R.P. O’Hayre, D.S. Ginley, “General mobility and carrier concentration relationship in transparent amorphous indium zinc oxide films”, Phys. Rev. B 77 (2008) 115215.
[86] L. Chernyak, K. Gartsman, D. Cahen, O.M. Stafsudd, “Electronic effects of ion mobility in semiconductors: Semionic behavior of CuInSe2”, J. Phys. Chem. Solids 56(9) (1995) 1165.
[87] E. Moons, T. Engelhard, D. Cahen, “Ohmic contacts to p-CuInSe2 crystals”, J. Electron. Mater. 22(3) (1993) 275.
[88] H.J. Moller: Semiconductors for Solar Cells, Artech House, London (1993).
[89] M.E. Fayed, L. Otten: Handbook of Powder Science & Technology, Chapman & Hall (1997).
[90] E.M. Levin, C.R. Robbins, H.F. McMurdie: Phase Diagrams for Ceramics, 5th ed., The American Ceramic Society (1985).
[91] S. Schorr, G. Geandier, “In-situ investigation of the temperature dependent structural phase transition in CuInSe2 by synchrotron radiation”, Cryst. Res. Technol. 41(5) (2006) 450.
[92] J.C. Mikkelsen, “Ternary phase relations of the chalcopyrite compound CuGaSe2”, J. Electron. Mater. 10(3) (1981) 541.
[93] S. Schorr, G. Geandier, B.V. Korzun, “Some are different from others: high temperature structural phase transitions in ternary chalcopyrites”, Phys. Status Solidi C 3(8) (2006) 2610.
[94] L.E. Fitzpatrick: Encyclopedia of Materials Characterization, Butterworth-Heinemann (1992).
[95] B.D. Cullity, S.R. Stock, Elements of X-Ray Diffraction, 3rd ed., Prentice-Hall (2001).
[96] S. Wartewig: IR and Raman Spectroscopy, Wiley-VCH GmbH & Co. KGaA (2003).
[97] R.E. Van-Grieken, A.A. Markowicz: Handbook of X-ray photoelectron spectroscopy, Marcel Dekker Inc. (2002).
[98] B.G. Yacobi: Semiconductor Materials, an Introduction to Basic Principles, Kluwer Academic Pub. (2003).
[99] A. Virtuani, E. Lotter, M. Powalla, U. Rau, J. H. Werner, M. Acciarri, “Influence of Cu content on electronic transport and shunting behavior of Cu(In,Ga)Se2 solar cells”, J. Appl. Phys. 99 (2006) 014906.
[100] D.Y. Lee, M.S. Kim, L. Larina, B.T. Ahn, “Effect of Cu content on the photovoltaic properties of Cu(In,Ga)Se2 solar cells prepared by the evaporation of binary selenide sources”, Electron. Mater. Lett. 4 (2008) 13.
[101] I. Dirnstorfer, D.M. Hofmann, D. Meister, B.K. Meyer, W. Riedl, F. Karg, “Postgrowth thermal treatment of CuIn(Ga)Se2: Characterization of doping levels in In-rich thin films”, J. Appl. Phys. 85 (1999) 1423.
[102] S.B. Zhang, S.H. Wei, A. Zunger, “Stabilization of ternary compounds via ordered arrays of defect Pairs”, Phys. Rev. Lett. 78(21) (1997) 4059.
[103] A.F. Wells: Structural Inorganic Chemistry, 5th ed., Clarendon Press, Oxford (1984).
[104] O. Aissaoui, S. Mehdaoui, L. Bechiri, M. Benabdeslem, N. Benslim, A. Amara, A. Otmani, K. Djessas, X. Portier, “Study of polycrystalline bulk CuIn1–xGaxTe2”, J. Lumin. 131 (2011) 109.
[105] F.Q. Huang, M.L. Liu, C. Yang, “Highly enhanced p-type electrical conduction in wide bandgap Cu1+xAl1-xS2 polycrystals”, Sol. Energy Mater. Sol. Cells 95 (2011) 2924.
[106] L. Djellal, A. Bouguelia, M. Trari, “Physical and photo-electrochemical properties of p-CuInSe2 bulk material”, Mater. Chem. Phys. 109 (2008) 99.
[107] M.L. Liu, F.Q. Huang, L.D. Chen, Y.M. Wang, “p-type transparent conductor: Zn-doped CuAlS2”, Appl. Phys. Lett. 90 (2007) 072109.
[108] B. Tell, J.L. Shay, H.M. Kasper, “Room-temperature electrical properties of ten I-III-VI2 semiconductors”, J. Appl. Phys. 43 (1972) 2469.
[109] S.B. Zhang, S.H. Wei, A. Zunger, “A phenomenological model for systematization and prediction of doping limits in II–VI and I–III–VI2 compounds”, J. Appl. Phys. 83 (1998) 3192.
[110] K. Ramanathan, R. Noufi, J. Granata, J. Webb, J. Keane, “Prospects for in situ junction formation in CuInSe2 based solar cells”, Sol. Energy Mater. Sol. Cells 55 (1998) 15.
[111] C. Yang, M. Qin, Y. Wang, D. Wan, F. Huang, J. Lin, “Observation of an intermediate band in Sn-doped chalcopyrites with wide-spectrum solar response”, Sci. reports 3 (2013) 1286.
[112] M. Mathewa, M. Gopinath, C.S. Kartha, K.P. Vijayakumar, Y. Kashiwaba, T. Abe, “Tin doping in spray pyrolysed indium sulfide thin films for solar cell applications”, Sol. Energy 84 (2010) 888.
[113] J.E. Jaffe, A. Zunger, “Anion displacements and the band-gap anomaly in ternary ABC2 chalcopyrite semiconductors”, Phys. Rev. B 27 (1983) 5176.
[114] J.E. Jaffe, A. Zunger, “Theory of the band-gap anomaly in ABC2 chalcopyrite semiconductors”, Phys. Rev. B 29 (1984) 1882.
[115] X.C. Ming, S. Yun, L.F. Yan, Z. Li, X.Y. Ming, H. Qing, L.H. Tu, “Composition-induced structural modifications in the quaternary CuIn1−xGaxSe2 thin films: Bond properties versus Ga content”, Chin. Phys. Soc. 16 (2007) 788.
[116] R.D. Shannon, “Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides”, Acta Cryst. A32 (1976) 751.
[117] Y. Wang, H. Gong, “Cu2ZnSnS4 synthesized through a green and economic process”, J. Alloy. Compd. 509 (2011) 9627.
[118] W. Zhang, W. Yu, L. Zhang, H. Yang, W. Fu, M. Li, Y. Li, “Synthesis and characterization of Cu2ZnSnSe4 nanotube arrays on fluorine-doped tin oxide glass substrates”, Superlattices Microstruct. 52 (2012) 653.
[119] M. Cao, Y. Shen, “A mild solvothermal route to kesterite quaternary Cu2ZnSnS4 nanoparticles”, J. Cryst. Growth 318 (2011) 1117.
[120] R.W. Keyes, “Correlation between mobility and effective mass in semiconductors”, J. Appl. Phys. 30 (1959) 454.
[121] V. Kheraj, K.K. Patel, S.J. Patel, D.V. Shah,“Synthesis and characterization of copper zinc tin sulphide (CZTS) compound for absorber material in solar cells”, J. Cryst. Growth 362 (2013) 174.
[122] S.M. Pawar, A.V. Moholkar, I.K. Kim, S.W. Shin, J.H. Moon, J.I. Rhee, J.H. Kim, “Effect of laser incident energy on the structural, morphological and optical properties of Cu2ZnSnS4 (CZTS) thin films”, Curr. Appl. Phys. 10(2) (2010) 565.
[123] D.H. Kuo, H.P. Wu, “Preparation and analysis of sputtered Cu2ZnSnSe4 thin films”, Adv. Mater. Res. 463- 464 (2012) 602.
[124] R.S. Becker, T. Zheng, J. Elton, M. Saeki, “Synthesis and photoelectrochemistry of In2S3”, Sol. Energy Mater. 13 (1986) 97.
[125] L.L. Kerr, S.S. Li, S.W. Johnston, T.J. Anderson, O.D. Crisalle, W.K. Kima, J. Abushama, R.N. Noufi, “Investigation of defect properties in Cu(In,Ga)Se2 solar cells by deep-level transient spectroscopy”, Solid-State Electronics 48 (2004) 1579.
[126] M. Igalson, P. Zabierowski, D. Przado, A. Urbaniak, M. Edoff, W.N. Shafarmanc, “Understanding defect-related issues limiting efficiency of CIGS solar cells”, Sol. Energy Mater. Sol. Cells 93 (2009) 1290.
[127] J.I. Langford, A.J.C. Wilson, “Scherrer after sixty years: A survey and some new results in the determination of crystallite size”, J. Appl. Crystallogr. 11 (1978) 102.
[128] O. Aissaoui, S. Mehdaoui, L. Bechiri, M. Benabdeslem, N. Benslim, A. Amara, A. Otmani, K. Djessas, X. Portier, “Study of polycrystalline bulk CuIn1–xGaxTe2”, J. Lumin. 131 (2011) 109.
[129] C. Rincon, S.M. Wasim, G. Marin, J.M. Delgado, J.R. Huntzinger, A. Zwick, J. Galibert, “Raman spectra of the ordered vacancy compounds CuIn3Te5 and CuGa3Se5”, Appl. Phys. Lett. 73 (1998) 441.
[130] M. Monsefi, D.H. Kuo, “A p → n transition for Sn-doped Cu(In,Ga)Se2 bulk materials”, J. Solid State Chem. 204 (2013) 108.
[131] C.D. Wagner, W.M. Riggs, L.E. Davis, J.F. Moulder, G.E. Muilenberg: Handbook of X-Ray Photoelectron Spectroscopy, Perkin-Elmer, Massachusetts (1979).
[132] S. Chen, X.G. Gong, A. Walsh, S. Wei, “Defect physics of the kesterite thin-film solar cell absorber Cu2ZnSnS4”, Appl. Phys. Lett. 96 (2010) 021902.
[133] Y. Terao, H. Sasabe, C. Adachi, “Correlation of hole mobility, exciton diffusion length, and solar cell characteristics in phthalocyanine/fullerene organic solar cells”, Appl. Phys. Lett. 90 (2007) 103515.
[134] P. Peumans, A. Yakimov, and S.R. Forrest, “Small molecular weight organic thin-film photodetectors and solar cells”, J. Appl. Phys. 93 (2003) 3693.
[135] K. Matsubara, A. Yamada, S. Ishizuka, K. Sakurai, H. Tampo, Y. Kimura, S. Nakamura, M. Yonemura, H. Nakanishi, S. Niki, “Wide-gap CIGS solar cells with Zn1-yMgyO transparent conducting film”, MRS Proceed. 865 (2005) F14.6.
[136] H. Saito, H. Chazono, H. Kishi, N. Yamaoka, “X7R multilayer ceramic capacitors with nickel electrodes”, Jpn. J. Appl. Phys. 30 (1991) 2307.
[137] D.H. Kuo, C.H. Wang, W.P. Tsai, “Donor and acceptor co-substituted BaTiO3 for nonreducible multilayer ceramic capacitors”, Ceram. Int. 32 (2006) 1.
[138] A. Virtuani, E. Lotter, M. Powalla, U. Rau, J. H. Werner, M. Acciarri, “Influence of Cu content on electronic transport and shunting behavior of Cu(In,Ga)Se2 solar cells”, J. Appl. Phys. 99 (2006) 014906.
[139] J. Liu, D.M. Zhuang, M.J. Cao, C.Y. Wang, M. Xie, X.L. Li, “Preparation and characterization of Cu(In,Ga)Se2 thin films by selenization of Cu0.8Ga0.2 and In2Se3 precursor films”, Int. J. Photoenergy 149210 (2012) 1.
[140] S. Lany, A. Zunger, “Anion vacancies as a source of persistent photoconductivity in II–VI and chalcopyrite semiconductors”, Phys. Rev. B 72 (2005) 035215.
[141] S. Lany, A. Zunger, “Light- and bias-induced metastabilities in Cu(In,Ga)Se2 based solar cells caused by the (VSe-VCu) vacancy complex”, J. Appl. Phys. 100 (2006) 113725.
[142] F. Smaili, M. Kanzari, B. Rezig, “Characterization of CuIn1−xAlxS2 thin films prepared by thermal evaporation”, Mater. Sci. Eng. C 28 (2008) 954.
[143] J. Olejniček, C.A. Kamler, S.A. Darveau, C.L. Exstrom, L.E. Slaymaker, A.R. Vandeventer, N.J. Ianno, R.J. Soukup, “Formation of CuIn1−xAlxSe2 thinfilms studied by Raman scattering”, Thin Solid Films 519 (2011) 5329.
[144] M. Tsega, D.H. Kuo, “Reactive sintering of Cu2ZnSnSe4 pellets at 600 ˚C with double sintering aids of Sb2S3 and Te”, J. Alloy. Compd. 580 (2013) 217.
[145] M. Monsefi, D.H. Kuo, “Influence of Cu content on the n → p transition of 15% Sn-doped Cux(In,Ga)Se2 bulk materials”, J. Alloy. Compd. 580 (2013) 348.