Due to the energy crisis, we rush into the solar cell research and development. Fulfillment of energy is an issue that is always covered by each of the countries, coupled with the increasing rate of world population growths, the energy consumption will continue to increase. The solar cell is one of the best choices, solar cells have been studied for more than fifty years but the last decade has seen the drastic growth in the research and development in the sector and because of that, now we have so many different types of solar cells design with megawatt production capabilities.
The main objective of this study is to explore the modern solar cell design in order to fulfill the energy consumption that every year always increases consisting of readily available, non-toxic material, and low-cost production, so we developed a copper zinc tin selenide (Cu2ZnSnSe4, CZTSe) and copper antimony sulfide (CuSbS2, CAS).
This work has included three parts. The first parts deal with the thin film solar cell based on p-CuSbS2 together with Cd-free GaN/InGaN bilayer. CuSbS2 thin film solar cell with 2.99% efficiency has been demonstrated by using the Cd-free GaN and In0.15Ga0.85N as n-type semiconductor bi-layer. CuSbS2 films on the TiN-coated Mo/glass substrates were made by co-sputtering technique at 300 oC with a cermet target of (Cu + Sb2S3) operated at 50 – 60 W and a metal target of Cu at 2 W, followed by thermal annealing at 350–450 oC for 1 h. The effects of processing conditions on the growth behavior, microstructural characteristics, and electrical properties of CuSbS2 films had been investigated. Solar cell devices were fabricated by depositing ~50 nm GaN and ~300 nm In0.15Ga0.85N layers with low temperature radio-frequency (RF) sputtering method, followed by RF sputtering 300–400 nm indium-tin-oxide (ITO) for front contact and pasting silver glue for electric contacts. The CuSbS2 thin film sputtered at 55 W had a [Cu]/[Sb] ratio of 0.80 with co-exists of the Sb2S3, and had a hole concentration of 1.41 × 1018 cm-3, an electrical conductivity 1.8 Scm-1, and mobility of 8 cm2 V-1 s-1. The efficiency of the solar cell device had a 3.83-fold increase if the p-CuSbS2/CdS/n-ZnO system had its conventionally designed CdS/n-type ZnO layer replaced by n-type GaN/In0.15Ga0.85N bilayer.
The second part gives an insight of the characterization of Ag-doped Cu2ZnSnSe4 bulks material and their application as thin film semiconductor in solar cells. Ag-doped CZTSe bulks and thin films with the (Cu2-xAgx)ZnSnSe4 (Ag-x-CZTSe) formula at x = 0, 0.1, 0.2, 0.3, and 0.4 were prepared at 600 ˚C by reactive sintering and selenization. We successfully demonstrated Ag-doped CZTSe materials without any different result between bulks preparation and thin films devices. Defect chemistry was studied by measuring structural and electrical properties of Ag-doped CZTSe as a function of dopant concentration. The enhanced of the device performance is shown with the increasing of Ag content to the CZTSe. The films had a stack structure of Ag/ITO/ZnO/CdS/Ag-CZTSe/Mo/soda-lime glass substrate. The efficiencies of Ag-x-CZTSe thin film solar cells at x= 0, 0.1, 0.2, 0.3 and 0.4 were 1.90, 2.4, and 3.4, 3.1, and 2.9%, respectively.
In the third part, germanium substitution effect on the property and performance of Cu2ZnSnSe4 thin films and its solar cell having absorber layer made by sputtering with single metallic target plus selenization. We report on the germanium substitution effect on the Cu2ZnSnSe4 (CZTSe) solar cell performance with absorber layer prepared by sputtering with a single metallic target plus further selenization. Ge-doped CZTSe thin films with the Cu2Zn(Sn1-xGex)Se4 (Ge-x-CZTSe) formula at x = 0, 0.05, 0.1, 0.15, and 0.2 were selenized at 600 ˚C. Defect chemistry was studied by measuring the structural, electrical, and optical properties of Ge-doped CZTSe as a function of dopant concentration. The enhanced device performance was shown with the increased Ge content to CZTSe. The solar cell was fabricated with a stack structure of Ag/ITO/ZnO/CdS/Ge-CZTSe/Mo/soda-lime glass substrate. The efficiencies of Ge-x-CZTSe thin film solar cells at x= 0, 0.05, 0.1, 0.15, and 0.2 were 1.90, 2.35, and 3.32, 4.64, and 4.24%, respectively. The further improvement in conversion efficiency of 7.23% was achieved by incorporating a NaF layer between the Mo bottom electrode and Ge-x-CZTSe absorber to form a Mo-NaF bilayer.

Due to the energy crisis, we rush into the solar cell research and development. Fulfillment of energy is an issue that is always covered by each of the countries, coupled with the increasing rate of world population growths, the energy consumption will continue to increase. The solar cell is one of the best choices, solar cells have been studied for more than fifty years but the last decade has seen the drastic growth in the research and development in the sector and because of that, now we have so many different types of solar cells design with megawatt production capabilities.
The main objective of this study is to explore the modern solar cell design in order to fulfill the energy consumption that every year always increases consisting of readily available, non-toxic material, and low-cost production, so we developed a copper zinc tin selenide (Cu2ZnSnSe4, CZTSe) and copper antimony sulfide (CuSbS2, CAS).
This work has included three parts. The first parts deal with the thin film solar cell based on p-CuSbS2 together with Cd-free GaN/InGaN bilayer. CuSbS2 thin film solar cell with 2.99% efficiency has been demonstrated by using the Cd-free GaN and In0.15Ga0.85N as n-type semiconductor bi-layer. CuSbS2 films on the TiN-coated Mo/glass substrates were made by co-sputtering technique at 300 oC with a cermet target of (Cu + Sb2S3) operated at 50 – 60 W and a metal target of Cu at 2 W, followed by thermal annealing at 350–450 oC for 1 h. The effects of processing conditions on the growth behavior, microstructural characteristics, and electrical properties of CuSbS2 films had been investigated. Solar cell devices were fabricated by depositing ~50 nm GaN and ~300 nm In0.15Ga0.85N layers with low temperature radio-frequency (RF) sputtering method, followed by RF sputtering 300–400 nm indium-tin-oxide (ITO) for front contact and pasting silver glue for electric contacts. The CuSbS2 thin film sputtered at 55 W had a [Cu]/[Sb] ratio of 0.80 with co-exists of the Sb2S3, and had a hole concentration of 1.41 × 1018 cm-3, an electrical conductivity 1.8 Scm-1, and mobility of 8 cm2 V-1 s-1. The efficiency of the solar cell device had a 3.83-fold increase if the p-CuSbS2/CdS/n-ZnO system had its conventionally designed CdS/n-type ZnO layer replaced by n-type GaN/In0.15Ga0.85N bilayer.
The second part gives an insight of the characterization of Ag-doped Cu2ZnSnSe4 bulks material and their application as thin film semiconductor in solar cells. Ag-doped CZTSe bulks and thin films with the (Cu2-xAgx)ZnSnSe4 (Ag-x-CZTSe) formula at x = 0, 0.1, 0.2, 0.3, and 0.4 were prepared at 600 ˚C by reactive sintering and selenization. We successfully demonstrated Ag-doped CZTSe materials without any different result between bulks preparation and thin films devices. Defect chemistry was studied by measuring structural and electrical properties of Ag-doped CZTSe as a function of dopant concentration. The enhanced of the device performance is shown with the increasing of Ag content to the CZTSe. The films had a stack structure of Ag/ITO/ZnO/CdS/Ag-CZTSe/Mo/soda-lime glass substrate. The efficiencies of Ag-x-CZTSe thin film solar cells at x= 0, 0.1, 0.2, 0.3 and 0.4 were 1.90, 2.4, and 3.4, 3.1, and 2.9%, respectively.
In the third part, germanium substitution effect on the property and performance of Cu2ZnSnSe4 thin films and its solar cell having absorber layer made by sputtering with single metallic target plus selenization. We report on the germanium substitution effect on the Cu2ZnSnSe4 (CZTSe) solar cell performance with absorber layer prepared by sputtering with a single metallic target plus further selenization. Ge-doped CZTSe thin films with the Cu2Zn(Sn1-xGex)Se4 (Ge-x-CZTSe) formula at x = 0, 0.05, 0.1, 0.15, and 0.2 were selenized at 600 ˚C. Defect chemistry was studied by measuring the structural, electrical, and optical properties of Ge-doped CZTSe as a function of dopant concentration. The enhanced device performance was shown with the increased Ge content to CZTSe. The solar cell was fabricated with a stack structure of Ag/ITO/ZnO/CdS/Ge-CZTSe/Mo/soda-lime glass substrate. The efficiencies of Ge-x-CZTSe thin film solar cells at x= 0, 0.05, 0.1, 0.15, and 0.2 were 1.90, 2.35, and 3.32, 4.64, and 4.24%, respectively. The further improvement in conversion efficiency of 7.23% was achieved by incorporating a NaF layer between the Mo bottom electrode and Ge-x-CZTSe absorber to form a Mo-NaF bilayer.

1. Future world energy demand driven by trends in developing countries (2013)
https://www.eia.gov/todayinenergy/detail.php?id=14011. Accessed 31 Aug 2017.
2. The Hidden Costs of Fossil Fuels. http://www.ucsusa.org/clean-energy/coal-and-other-fossil-fuels/hidden-cost-of-fossils#.Wg2VOnNEnIU (2016) [cited 2017 September 15].
3. A.R. Jha, Solar cell technology and applications, CRC Press, Boca Raton (2010).
4. GTM research: global solar pv installations grew 34% in 2015 (2015)
https://www.greentechmedia.com/articles/read/gtm-research-global-solar-pv-installations-grew-34-in-2015#gs.Jg0Dxj8. [cited 2017 October 13th].
5. E. Płaczek-Popko, Top PV market solar cells 2016. Opto-Electronics Review, 25 (2017) 55-64.
6. 30.2 Percent Efficiency – New record for silicon-based multi-junction solar cell (2016)
https://www.ise.fraunhofer.de/en/press-media/press-releases/2016/30-2-percent-efficiency-new-record-for-silicon-based-multi-junction-solar-cell.html [cited 2017 October 13].
7. Solar cell (2017) https://en.wikipedia.org/wiki/Solar_cell. [cited 2017 October 13th].
8. Time line of solar cellls (2017) https://en.wikipedia.org/wiki/Timeline_of_solar_cells. [cited 2017 Octobert 13th].
9. D.A. Ras, T.Kirchartz, U. Rau, Advanced characterization techniques for thin film solar cells, Wiley-VCH, Weinheim: Germany (2011).
10. S. Sharma, K.K. Jain, A. Sharma, Solar cells: in research and applications—A Review. Materials Sciences and Applications, 6 (2015) 1145-1155.
11. J. Zhao, Recent advances of high-efficiency single crystalline silicon solar cells in processing technologies and substrate materials. Solar Energy Materials and Solar Cells, 82 (2004) 53-64.
12. R. Munir, G.S. Jung, B.T. Ahn. Growth and characterization of Cu2ZnSnSe4 (CZTSe) thin films by sputtering of binary selenides and selenization, Proceedings of the Materials Research Society of Korea Conference. 2012.
13. First Solar Hits Record 22.1% Conversion Efficiency for CdTe Solar Cell (2016)
https://www.greentechmedia.com/articles/read/First-Solar-Hits-Record-22-1-Conversion
Efficiency-For-CdTe-Solar-Cell#gs.O2HOoOg [cited 2017 October 13].
14. Solar frontier achieves world record thin-film solar cell efficiency: 22.3%. (2015) http://www.solar-frontier.com/eng/news/2015/C051171.html [cited 2017 January 19].
15. W. Wang, M.T. Winkler, O. Gunawan, T. Gokmen, T.K. Todorov, Y. Zhu, D.B. Mitzi, Device characteristics of CZTSSe thin-film solar cells with 12.6% efficiency, Advanced Energy Materials, 4 (2014) 1301465.
16. J. Engman, Experimental study of Cu2ZnSn(Se,S)4 thin films for solar cell applications, Thesis, Institutionen för teknikvetenskaper: Department of Engineering Sciences (2011).
17. C. Tablero, Electronic and optical property analysis of the cu–sb–s tetrahedrites for high-efficiency absorption devices. The Journal of Physical Chemistry C, 118 (2014) 15122-15127.
18. A.C. Rastogi, N.R. Janardhana, Properties of CuSbS2 thin films electrodeposited from ionic liquids as p-type absorber for photovoltaic solar cells. Thin Solid Films, 565 (2014) 285-292.
19. A. Rabhi, M. Kanzari, B. Rezig, Optical and structural properties of CuSbS2 thin films grown by thermal evaporation method. Thin Solid Films, 517 (2009) 2477-2480.
20. T. Maeda, T. Wada, First-principles study of electronic structure of CuSbS2 and CuSbSe2 photovoltaic semiconductors. Thin Solid Films, 582 (2015) 401-407.
21. T.S. Reddy, R. Amiruddin, M.C.S. Kumar, Deposition and characterization of Cu2SnS3 thin films by co-evaporation for photovoltaic application. Solar Energy Materials and Solar Cells, 143 (2015) 128-134.
22. A.W. Welch, P.P. Zawadzki, S. Lany, C.A. Wolden, A. Zakutayev, Self-regulated growth and tunable properties of CuSbS2 solar absorbers. Solar Energy Materials and Solar Cells, 132 (2015) 499-506.
23. Y.R. Lazcano, M.T.S. Nair, P.K. Nair, Photovoltaic p-i-n Structure of Sb2S3 and CuSbS2 absorber films obtained via chemical bath deposition. Journal of The Electrochemical Society, 152 (2005) G635-G638.
24. J. Zhou, G.Q. Bian, Q.Y. Zhua, Y. Zhanga, C.Y. Li, J. Da, Solvothermal crystal growth of CuSbQ2 (Q=S, Se) and the correlation between macroscopic morphology and microscopic structure. Journal of Solid State Chemistry, 182 (2009) 259-264.
25. D. Colombara, L.M. Peter, K.D. Rogers, J.D. Painter, S. Roncallo, Formation of CuSbS2 and CuSbSe2 thin films via chalcogenisation of Sb–Cu metal precursors. Thin Solid Films, 519 (2011) 7438-7443.
26. I. Popovici, A. Duta., tailoring the composition and properties of sprayed CuSbS2 Thin films by using polymeric additives. Inter. J. Photoenergy, 2012 (2012) 962649.
27. T. Markvart, L. Castaner, Solar Cells: Materials, Manufacture and Operation, Elsevier Science: Netherlands (2004).
28. P. Würfel, Physics of Solar Cells: From Principles to New Concepts, Wiley-VCH Verlag GmbH: Germany (2007).
29. M. Tsega, M., Densification and characterizations of un-doped and doped Cu2ZnSn(S,Se)4 bulk materials, Dissertation, National Taiwan University of Science and Technology: Materials Science and Engineering (2013).
30. S. Chen, A. Walsh , X.G. Gong, S.H. Wei, Classification of lattice defects in the kesterite Cu2ZnSnS4 and Cu2ZnSnSe4 earth-abundant solar cell absorbers. Adv Mater, 25 (2013) 1522-39.
31. W. Septina, S. Ikeda, Y. Iga, T. Harada, M. Matsumura, Thin film solar cell based on CuSbS2 absorber fabricated from an electrochemically deposited metal stack. Thin Solid Films, 550 (2014) 700-704.
32. L. Wan, C. Ma, K. Hu, R. Zhou, X. Mao, S. Pan, L.H. Wong, J. Xu, Two-stage co-evaporated CuSbS2 thin films for solar cells. Journal of Alloys and Compounds, 680 (2016) 182-190.
33. S. Banu, S.J. Ahna, S.K. Ahna, K. Yoona, A. Cho, Fabrication and characterization of cost-efficient CuSbS2 thin film solar cells using hybrid inks. Solar Energy Materials and Solar Cells,. 151 (2016) 14-23.
34. A.W. Welch1, L.L. Baranowski, P. Zawadzki1, C. DeHart, S. Johnston, S. Lany, C.A. Wolden, A. Zakutayev, Accelerated development of CuSbS2 thin film photovoltaic device prototypes. Progress in Photovoltaics: Research and Applications, (2016).
35. W.L. Chen, D.H. Kuo, T.T.A. Tuan, Preparation of CuSbS2 thin films by co-sputtering and solar cell devices with band gap-adjustable n-type InGan as a substitute of ZnO. Journal of Electronic Materials, 45 (2015) 688-694.
36. W. Gong, T. Tabata, K. Takei, M. Morihama, T. Maeda, T. Wada, Crystallographic and optical properties of (Cu, Ag)2ZnSnS4 and (Cu, Ag)2ZnSnSe4 solid solutions, physica status solidi (c), 12 (2015) 700-703.
37. C.J. Hages, M.J. Koeper, R. Agrawal, Optoelectronic and material properties of nanocrystal-based CZTSe absorbers with Ag-alloying, Solar Energy Materials and Solar Cells, 145 (2016) 342-348.
38. T. Gershon, Y.S. Lee, P. Antunez, R. Mankad, S. Singh, D. Bishop, O. Gunawan, M. Hopstaken, R. Haight, Photovoltaic materials and devices based on the alloyed kesterite absorber (AgxCu1-x)2ZnSnSe4, Advanced Energy Materials, 6 (2016) 1502468.
39. Y. Zhao, X. Han, B. Xu,W. Li, J. Li, Jiajia Li, M. Wang, C. Dong, P. Ju, Junshuai Li, Enhancing open-circuit voltage of solution CZTSSe solar cell with Ag substitution. IEEE JOURNAL OF PHOTOVOLTAICS, 7 (2017) 874-881.
40. A.C. Lokhande, R.B.V. Chalapathy, J.S. Jang, P.T. Babar, M.G. Gang, C.D. Lokhande, J.H. Kim, Fabrication of pulsed laser deposited Ge doped CZTSSe thin film based solar cells: Influence of selenization treatment, Solar Energy Materials and Solar Cells, 161 (2017) 355-367.
41. S. Kim, K.M. Kim, H. Tampo, H. Shibata, K. Matsubara, S. Niki, Ge-incorporated Cu2ZnSnSe4 thin-film solar cells with efficiency greater than 10%, Solar Energy Materials and Solar Cells, 144 (2016) 488-492.
42. M. Neuschitzer, J. Marquez, S. Giraldo, M. Dimitrievska, M. Placidi, I. Forbes, V. Izquierdo-Roca, A. Pérez-Rodriguez, E. Saucedo, Voc boosting and grain growth enhancing Ge-doping strategy for Cu2ZnSnSe4 photovoltaic absorbers, The Journal of Physical Chemistry C, 120 (2016) 9661-9670.
43. D.B. Khadka, S. Kim, J. Kim, Effects of Ge alloying on device characteristics of kesterite-based CZTSSe thin film solar cells, The Journal of Physical Chemistry C, 120 (2016) 4251-4258.
44. S. Hemavibool, The microstructure of synthetic aggregate produced from waste materials and its influence on the properties of concrete, Thesis, University of Leeds (2007).
45. Suryanarayana, C. Norton, M. Grant, X-Ray diffraction : a practical approach, Plenum Press: New York and London (1998).
46. R. Precht, S. Stolz, E. Mankel, T. Mayer, W. Jaegermanna, R. Hausbranda, Electronic structure and electrode properties of tetracyanoquinodimethane (TCNQ): a surface science investigation of lithium intercalation into TCNQ. Physical chemistry chemical physics, 17 (2015) 6588-6596.
47. K.A. Borup, E. S. Toberer, L.D. Zoltan, G. Nakatsukasa, M. Errico, J.P Fleurial, B.B. Iversen, G.J. Snyder, Measurement of the electrical resistivity and Hall coefficient at high temperatures. Rev Sci Instrum, 83 (2012) 123902.
48. L.J. Van der Pauw, Philips Research Reports (1958).
49. B.G. Yacobi, Semiconductor Materials, an Introduction to Basic Principles, Kluwer Academic Publishers: University of Toronto, Ontario, Canada: (2004).
50. K.M. Kim, H. Tampo, H. Shibata, S. Niki, Growth and characterization of coevaporated Cu2SnSe3 thin films for photovoltaic applications. Thin Solid Films, 536 (2013) 111-114.
51. Z. Tang, Y. Nukuib, K. Kosaka, N. Ashida, H. Uegaki, T. Minemoto, Reduction of secondary phases in Cu2SnSe3 absorbers for solar cell application. Journal of Alloys and Compounds, 608 (2014) 213-219.
52. A. Hussain, R. Ahmed, N. Ali, F.K. Butt, A. Shaari, W.N.W. Shamsuri, R. Khenata, D. Prakash, K.D. Verma, Post annealing effects on structural, optical and electrical properties of CuSbS2 thin films fabricated by combinatorial thermal evaporation technique. Superlattices and Microstructures, 89 (2016) 136-144.
53. Dufton, J.T., et al., Structural and electronic properties of CuSbS2 and CuBiS2: potential absorber materials for thin-film solar cells. Phys Chem Chem Phys, 14 (2012) 7229-33.
54. Y.R. Lazcano, M.T.S. Nair, P.K. Nair, CuSbS2 thin film formedthrough annealing chemically deposited Sb2S3–CuS thin film. Journal of Crystal Growth, 223 (2001) 399–406.
55. C. Garza, S. Shaji, A. Arato, E.P. Tijerina, G.A. Castillo, T.K.D. Roy, B. Krishnan, p-Type CuSbS2 thin films by thermal diffusion of copper into Sb2S3. Solar Energy Materials and Solar Cells, 95 (2011) 2001-2005.
56. Rabhi, A., M. Kanzari, B. Rezig, Growth and vacuum post-annealing effect on the properties of the new absorber CuSbS2 thin films. Materials Letters, 62 (2008) 576-3578.
57. R. E.O. Acosta, B. Krishnan, D. Avellaneda, S. Shaji, G. A. Castillo, T.K.D. Roy, B. Krishnan, CuSbS2 thin films by heating Sb2S3/Cu layers for PV applications. Journal of Materials Science: Materials in Electronics, 25 (2014) 4356-4362.
58. S. Manolache, A. Duta, L. Isac, M. Nanu, A. Goossens, J. Schoonman, The influence of the precursor concentration on CuSbS2 thin films deposited from aqueous solutions. Thin Solid Films, 515 (2007) 5957-5960.
59. J.A.R. Aquino, D.R.L. Vela, S. Shaji, D.A. Avellaneda, B. Krishnan, Spray pyrolysed thin films of copper antimony sulfide as photovoltaic absorber. physica status solidi (c), 13 (2016) 24-29.
60. V. Tunuguntla, W.C. Chena, T.D. Newmane, C.Y. Chen, M.C. Hsieh, S.H.Lu, C. Su, L.C. Chenc, K.H. Chen, Enhancement of charge collection at shorter wavelengths from alternative CdS deposition conditions for high efficiency CZTSSe solar cells. Solar Energy Materials and Solar Cells, 149 (2016) 49-54.
61. R.N. Bhattacharya, K. Ramanathan, Cu(In,Ga)Se2 thin film solar cells with buffer layer alternative to CdS. Solar Energy, 77 (2004) 679-683.
62. C. Schwartz , D. Nordlunda, T.C. Weng, D. Sokaras, L. Mansfield, A.S. Krishnapriyana, K. Ramanathand, K.E. Hurst, D. Prendergast, S.T. Christensen, Electronic structure study of the CdS buffer layer in CIGS solar cells by X-ray absorption spectroscopy: Experiment and theory. Solar Energy Materials and Solar Cells, 149 (2016) 275-283.
63. T. Nakada, M. Mizutani, Y. Hagiwara, A. Kunioka, High-effciency Cu(In,Ga)Se2 thin-film solar cells with a CBD-ZnS buffer layer. Solar Energy Materials & Solar Cells, 67 (2001) 255-260.
64. B. Monemar, Fundamental energy gap of GaN from photoluminescence excitation spectra. Physical Review B, 10 (1974) 676-681.
65. C.C. Li, D.H. Kuo, Effects of growth temperature on electrical and structural properties of sputtered GaN films with a cermet target. Journal of Materials Science: Materials in Electronics, 25 (2014) 1404-1409.
66. M. D. McCluskey, C.G. Van de Walle, C.P. Master, L.T. Romano, N.M. Johnson, Large band gap bowing of InxGa1-xN alloys. Applied Physics Letters, 72 (1998). 2725-2726.
67. O.Jani, I. Ferguson, C. Honsberg, S. Kurtz, Design and characterization of GaN∕InGaN solar cells. Applied Physics Letters, 91 (2007) 132117.
68. P.G. Moses, C.G. Van de Walle, Band bowing and band alignment in InGaN alloys. Applied Physics Letters, 96 (2010) 021908.
69. C.C. Li, D.H. Kuo, Y.S. Huang, The effect of temperature on the growth and properties of green light-emitting In0.5Ga0.5N films prepared by reactive sputtering with single cermet target. Materials Science in Semiconductor Processing, 29 (2015) 170-175.
70. T.T.A. Tuan, D.H. Kuo, K. Lin, G.Z. Li Temperature dependence of electrical characteristics of n-InxGa1−xN/p-Si hetero-junctions made totally by RF magnetron sputtering. Thin Solid Films, 589 (2015) 182-187.
71. Chalcostibite R060262 http://rruff.info/Chalcostibite [cited 2017 October 13th].
72. J.I. Pankove, Optical processes in semiconductors, Dover Inc: New York (1971).
73. Y.S. Lee, T. Gershon, O. Gunawan, T.K. Todorov, T. Gokmen, Y. Virgus, S.Guha, Cu2ZnSnSe4 thin-film solar cells by thermal co-evaporation with 11.6% efficiency and improved minority carrier diffusion length. Advanced Energy Materials, 5 (2015) 1401372.
74. S. Oueslati, G. Brammertz, M. Buffière, H. ElAnzeery, O. Touayar , C. Köble, J. Bekaert, M. Meuris, J.Poortmans, Physical and electrical characterization of high-performance Cu2ZnSnSe4 based thin film solar cells. Thin Solid Films, 582 (2015) 224-228.
75. J.M. Prieto, M.V. Yakushev, I. Forbes, J. Krustok, P.R. Edwards, V.D. Zhivulko, O.M. Borodavchenko, A.V. Mudryi, M. Dimitrievska, V.I. Roca, N.M. Pearsall, R.W. Martin, Impact of the selenisation temperature on the structural and optical properties of CZTSe absorbers. Solar Energy Materials and Solar Cells, 152 (2016) 42-50.
76. M. Placidi, M.E. Rodriguez, S.L. Marino, Y. Sanchez, S. Giraldo, L. Acebo, M. Neuschitzer, X.A. Rodríguez, E. Saucedo, Effect of rapid thermal annealing on the Mo back contact properties for Cu2ZnSnSe4 solar cells. Journal of Alloys and Compounds, 675 (2016) 158-162.
77. D.B. Mitzi, O. Gunawan, T.K. Todorov, K. Wang, S. Guha, The path towards a high-performance solution-processed kesterite solar cell. Solar Energy Materials and Solar Cells, 95 (2011) 1421-1436.
78. C.J. Hages, N.J. Carter, R. Agrawal, T. Unold, Generalized current-voltage analysis and efficiency limitations in non-ideal solar cells: Case of Cu2ZnSn(SxSe1−x)4 and Cu2Zn(SnyGe1−y)(SxSe1−x)4. Journal of Applied Physics, 115 (2014) 234504.
79. J. Lee , W. Lee, N.K. Shrestha, D.Y. Lee, I. Lima, S.H. Kang, Y.C. Nahe, S.H. Lee, W. Yi, S.H. Han, Influence of encapsulated electron active molecules of single walled-carbon nanotubes on superstrate-type Cu(In,Ga)Se2 solar cells. Materials Chemistry and Physics, 144 (2014) 49-54.
80. D.B. Khadka, S. Kim, J. Kim, Ge-alloyed CZTSe thin film solar cell using molecular precursor adopting spray pyrolysis approach. Rsc Advances, 6 (2016) 37621-37627.
81. J.H. Boyle, B.E. McCandless, W.N. Shafarman, R.W. Birkmire, Structural and optical properties of (Ag,Cu)(In,Ga)Se2 polycrystalline thin film alloys. Journal of Applied Physics, 115 (2014) 223504.
82. P.T. Erslev, J. Lee, G.M. Hanket, W.M. Shafarman, J.D.Cohen The electronic structure of Cu(In1−xGax)Se2 alloyed with silver. Thin Solid Films, 519 (2011) 296-7299.
83. W. Li, X. Liu, H. Cui, S. Huang, X. Hao, The role of Ag in (Ag,Cu)2ZnSnS4 thin film for solar cell application. Journal of Alloys and Compounds, 625 (2015) 277-283.
84. P.W. Shao, C.T. Li, K.C. Ho, K.W. Cheng, Catalytic and photoelectrochemical performances of Cu–Zn–Sn–Se thin films prepared using selenization of electrodeposited Cu–Zn–Sn metal precursors. Journal of Power Sources, 286 (2015) 47-57.
85. A.D. Saragih, D.H. Kuo, T.T.A. Tuan, Thin film solar cell based on p-CuSbS2 together with Cd-free GaN/InGaN bilayer. Journal of Materials Science: Materials in Electronics, 28 (2016) 2996-3003.
86. D.H. Kuo, J.T. Hsu, A.D. Saragih, Effects of the metallic target compositions on the absorber properties and the performance of Cu2ZnSnSe4 solar cell devices fabricated on TiN-coated Mo/glass substrates. Materials Science and Engineering: B, 186 (2014)p. 94-100.
87. C.M.S. Fella, J.A. Stückelberger, H. Hagendorfer, F.L. Mattina, L. Kranz, S. Nishiwaki, A.R. Uhl, Y.E. Romanyuk, A.N. Tiwari, Sodium Assisted sintering of chalcogenides and its application to solution processed Cu2ZnSn(S,Se)4 thin film solar cells. Chemistry of Materials, 2014. 26 (2014) 1420-1425.
88. H. Guo, Y. Cui, Q. Tian, S. Gao, G. Wang, D. Pan, Significantly enhancing grain growth in Cu2ZnSn(S,Se)4 absorber layers by insetting Sb2S3, CuSbS2, and NaSb5S8 thin films. Crystal Growth & Design, 15 (2015) 771-777.
89. H. Katagiri, K. Jimbo, W.S. Maw, K. Oishi, M. Yamazaki, H. Araki, A. Takeuchi, Development of CZTS-based thin film solar cells. Thin Solid Films, 517 (2009) 2455-2460.
90. T.K. Todorov, K.B. Reuter, D.B. Mitzi, High-efficiency solar cell with Earth-abundant liquid-processed absorber. Adv Mater, 22 (2010) E156-E159.
91. JCPDS (Joint Committee on Powder Diffraction Standards) Card no.00-052-0868.
92. B.D. Cullity, S.R.Stock, Elements of X-Ray Diffraction, 3rd edition. Prentice-Hall: New Jersey (2011).
93. R.D. Shannon, Revised Effective Ionic Radii and Systematic Studies of Interatomie Distances. Acta Cryst, A32 (1976) 751-756.
94. S. Chen, X.G. Gong, A. Walsh, S.H. Wei, Defect physics of the kesterite thin-film solar cell absorber Cu2ZnSnS4. Applied Physics Letters, 96 (2010) 021902.
95. A.R. Jeong, W. Jo, S. Jung, J. Gwak, J.H. Yun, Enhanced exciton separation through negative energy band bending at grain boundaries of Cu2ZnSnSe4 thin-films. Applied Physics Letters, 99 (2011) 082103.
96. T. Maeda, S. Nakamura, T. Wada, First principles calculations of defect formation in in-free photovoltaic semiconductors Cu2ZnSnS4 and Cu2ZnSnSe4. Japanese Journal of Applied Physics, 50 (2011) 04DP07.
97. J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray Photoelectron Spectroscopy, Physical Electronic Inc: Minnesota, United States of America (1995).
98. Y.F. Du, J.Q. Fan, W.H. Zhou, Z.J. Zhou, J. Jiao, S.X. Wu, One-step synthesis of stoichiometric Cu2ZnSnSe4 as counter electrode for dye-sensitized solar cells. ACS Appl Mater Interfaces, 4 (2012) 1796-802.
99. 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. Progress in Photovoltaics: Research and Applications, 21 (2013) 82-87.
100. W. Ki, H.W. Hillhouse, Earth-abundant element photovoltaics directly from soluble precursors with high yield using a non-toxic solvent. Advanced Energy Materials, 1 (2011) 732-735.
101. T. Todorov, D.B. Mitzi, Direct liquid coating of chalcopyrite light-absorbing layers for photovoltaic devices. European Journal of Inorganic Chemistry, 2010 (2010) 17-28.
102. S. Chen, A. Walsh, J.H. Yang, X. G. Gong, L. Sun, P.X. Yang, J.H. Chu, S.H. Wei, Compositional dependence of structural and electronic properties of Cu2ZnSn(S,Se)4 alloys for thin film solar cells. Physical Review B, 83(2011) 125201.
103. J.Gea, J. Jiang, P. Yang , C. Peng, Z. Huanga, S. Zuo, L. Yang, J. Chu, A 5.5% efficient co-electrodeposited ZnO/CdS/Cu2ZnSnS4/Mo thin film solar cell. Solar Energy Materials and Solar Cells, 125 (2014) 20-26.
104. A.D. Saragih, W. Wubet. H. Abdullah, A.K. Abay, D.H. Kuo, Characterization of Ag-doped Cu2ZnSnSe4 bulks material and their application as thin film semiconductor in solar cells. Materials Science and Engineering: B, 225 (2017) 45-53.
105. Q. Guoa, G.M. Ford, W.C. Yanga, C.J. Hages, H.W. Hillhouse, R. Agrawal, Enhancing the performance of CZTSSe solar cells with Ge alloying. Solar Energy Materials and Solar Cells, 105 (2012) 132-136.
106. Q. Shu, J.H. Yang, S. Chen, B. Huang, H. Xiang,1 X.G. Gong, S.H. Wei, Cu2Zn(Sn,Ge)Se4 and Cu2Zn(Sn,Si)Se4 alloys as photovoltaic materials: Structural and electronic properties. Physical Review B, 87 (2013) 115208.
107. J.Chen, W. Li, C. Yan, S. Huang, X. Hao, Studies of compositional dependent Cu2Zn(GexSn1−x)S4 thin films prepared by sulfurizing sputtered metallic precursors. Journal of Alloys and Compounds, 621 (2015) 154-161.
108. G.M. Ford, Q. Guo, R. Agrawal, H.W. Hillhouse, Earth abundant element Cu2Zn(Sn1−xGex)S4 nanocrystals for tunable band gap solar cells: 6.8% efficient device fabrication. Chemistry of Materials, 23 (2011) 2626-2629.
109. A.C. Miller, G.W. Simmons, Copper by XPS. Surf. Sci. Spectra, 2(1993) 55.
110. S.W. Gaarenstroom, N.Winograd, Initial and final state effects in the ESCA spectra of cadmium and silver oxides. J. Chem. Phys, 67 (1977) 3500.
111. B.R. Strohmeier, Zinc Aluminate (ZnAl2O4) by XPS. Surf. Sci. Spectra 3 (1994) 128.
112. P.H. Watts, J.E. Huheey, X-ray photoelectron spectroscopy of tin. II. allotropes of elemental tin. Inorg. Nucl. Chem. Lett, 10 (1974) 287-290.
113. M. Rubel, R.Haasch, P. Mrozek, A. Wieckowski, C. De Pauli, S. Trasatti, Characterization of IrO2.SnO2 thin layers by electron and ion spectroscopies. Vacuum, 45 (1994) 423-427.
114. N. Martensson., B. Reihl, O. Vogt, Binding energies and heat-of-formation data for USbxTe1-x and UAsxSe1-x compounds as derived from photoelectron spectroscopy. Phys. Rev. B, 25 (1982) 824-829.
115. K. Satoh, T. Takahashi., H.K. Yoshida, T. Sagawa, Bound states in copper-based Cu–Ge and Cu–Se alloys studied by x-ray photoelectron spectroscopy. J. Phys. Soc. Japan 54 (1985) 1214-1215.
116. T. Ma, G. Jiang, W. Liu, C. Zhu, Sodium doping effects on the crystalline and electrical properties of Cu2ZnSnSe4 thin films. Solar Energy, 115 (2015) 413-418.
117. J.V. Li, D. Kuciauskas, M.R. Young, I.L. Repins, Effects of sodium incorporation in Co-evaporated Cu2ZnSnSe4 thin-film solar cells. Applied Physics Letters, 102 (2013) 163905.