US 2013 0037111A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2013/0037111A1 Mitzi et al. (43) Pub. Date: Feb. 14, 2013 (54) PROCESS FOR PREPARATION OF HOIL 3L/8 (2006.01) ELEMENTAL CHALCOGEN SOLUTIONS C09D II/00 (2006.01) AND METHOD OF EMPLOYING SAD B82Y-3O/OO (2011.01) SOLUTIONS IN PREPARATION OF (52) U.S. Cl. ... 136/264; 438/95; 106/31.13; 252/182,32: KESTERITE FILMS 257/E31.027; 977/773 (75) Inventors: David Brian Mitzi, Mahopac, NY (US); (57) ABSTRACT Xiaofeng Qiu, Sleepy Hollow, NY (US) Techniques for preparing chalcogen-containing solutions (73) Assignee: International Business Machines using an environmentally benign borane-based reducing Corporation, Armonk, NY (US) agent and solvents under ambient conditions, as well as appli cation of these solutions in a liquid-based method for depo (21) Appl. No.: 13/207,248 sition of inorganic films having copper (Cu), Zinc (Zn), tin (Sn), and at least one of sulfur (S) and selenium (Se) are (22) Filed: Aug. 10, 2011 provided. In one aspect, a method for preparing a chalcogen containing solution is provided. The method includes the Publication Classification following steps. At least one chalcogen element, a reducing agent and a liquid medium are contacted under conditions (51) Int. C. Sufficient to produce a homogenous Solution. The reducing HOIL 31/032 (2006.01) agent (i) contains both boron and hydrogen, (ii) is substan C09K3/00 (2006.01) tially carbon free and (iii) is substantially metal free. 404 402 302 204 202 Substrate Patent Application Publication Feb. 14, 2013 Sheet 1 of 5 US 2013/00371.11 A1 100 Contact metal source(s) with the elemental chalcogen solution under conditions sufficient to form metal-chalcogen nanoparticles containing Cu, Sn, Zn and at least 102 one of S and Se. Suspend metal-chalcogen nanoparticles in chalcogen-containing solution to form 104 ink. Deposit ink on substrate. FIG. 1 Patent Application Publication Feb. 14, 2013 Sheet 2 of 5 US 2013/0037111A1 204 202 FIG 2 302 204 202 Substrate FIG. 3 404 402 302 204 202 Substrate FIG. 4 Patent Application Publication Feb. 14, 2013 Sheet 3 of 5 US 2013/0037111A1 500 Sesolubility in 5 mL Dipole Moment Dielectric (D) constant 200 Ethylene Glycol 4M/0.3g AB O 37.7 Methanol - 4M/0.35g AB - - - - - - - - - - - - - - 1.7 33 1-Methylimidazole 5M/0.4g AB 3.7 35 Tetrahydrofuran 2M/0.2g AB 4. 7.5 Aectone 5M/0.4g AB 5.1 . 21 Pyridine 4M/0.4g AB 5.3 : 12.5 2-Methoxyethanol 4M/0.3g AB 5.5 16.93 Dimethylformamide 4M/0.3g AB 6.4 36.7 Dimethylsulfoxide 2M/0.35g AB -----------......... .'; 7.2 46.7 Ammonium hydroxide 6M/0.42g AB 10.2 8O FIG. 5 Patent Application Publication Feb. 14, 2013 Sheet 4 of 5 US 2013/00371.11 A1 Nanoparticle layer On EHT = 10.00 kW Signal A = InLens Date 27 May 2011 Time:11:40:50 Mag 93.64 KX WD = 7.9mm FileName = xoAC21804tf FIG. 6 10000 an 1000 V CN Q M O 100 10 20 30 40 50 60 70 20 Degree FIG. 7 Patent Application Publication Feb. 14, 2013 Sheet 5 of 5 US 2013/00371.11 A1 800 OO frn EHT = 10.00 kV Signal A = InLens Date:23 Jun 2011 Time: 0:58:15 Mag 3688 KX WD = 7.3 mm FileName=xaAc320-13.tif FIG. 8 2.42% 45.65% 254.5 mV 20.8 mA/cm' -0.2 -0.1 0.0 O.1 0.2 0.3 0.4 Potential (V) FIG. 9 US 2013/00371 11 A1 Feb. 14, 2013 PROCESS FOR PREPARATION OF chalcogen by using hydrazine. See, for example, U.S. Pat. No. ELEMENTAL CHALCOGEN SOLUTIONS 4,122,030 issued to Smith et al., entitled “Formation of Col AND METHOD OF EMPLOYING SAD loidal Dispersions of Selenium by the Locus Control SOLUTIONS IN PREPARATION OF Method, U.S. Pat. No. 6,379,585 B1 issued to Vecht et al., KESTERITE FILMS entitled “Preparation of Sulphides and Selenides. U.S. Pat. No. 7,094,651 B2, issued to Mitzi et al., entitled “Hydrazine FIELD OF THE INVENTION Free Solution Deposition of Chalcogenide Films. U.S. Patent Application Publication No. 2009/0145482 A1, filed 0001. The present invention relates to techniques for pre by Mitzi et al., entitled “Photovoltaic Device with Solution paring chalcogen-containing Solutions using an environmen Processed Chalcogenide Absorber Layer” and U.S. Pat. No. tally benign borane-based reducing agent and solvents under 6,875,661 B2. Colloidal and pure-solution elemental chalco ambient conditions, as well as application of these solutions gen liquids have also been prepared directly from elemental in a liquid-based method for deposition of inorganic films chalcogen by using organic ligands, such as trioctylphos having copper (Cu), Zinc (Zn), tin (Sn), and at least one of phine oxide (TOPO), oleylamine and oleic acid. See, for sulfur (S) and selenium (Se) and more particularly, to tech example, C. B. Murray, D. J. Norris, and M. G. Bawendi, niques for deposition of kesterite-type Cu-Zn-Sn—(Se.S) “Synthesis and Characterization of Nearly Monodisperse materials and improved photovoltaic devices based on these CdE (E-S, Se, Te) Semiconductor Nanocrystallites. J. Am. films. Chem. Soc., 115, 8706-8715 (1993), M. V. Kovalenko, M. Scheele, D.V.Talapin, "Colloidal Nanocrystals with Molecu BACKGROUND OF THE INVENTION lar Metal Chalcogenide Surface Ligands. Science, 324, 0002 Thin-film chalcogenide-based solar cells provide a 1417-1420 (2009) and Q. Guo, G. M. Ford, W. Yang, B. C. promising pathway to cost parity between photovoltaic and Walker, E. A. Stach, H. W. Hillhouse, R. Agrawal, “Fabrica conventional energy sources. However, in order to keep pro tion of 7.2% Efficient CZTSSe Solar Cells Using CZTS duction costs down for thin-film chalcogenide-based Solar Nanocrystals,” J. Am. Chem. Soc., 132, 17384-17386 (2010). cell production and thus make this technology a viable alter 0006. However, hydrazine is an explosive and highly toxic native for conventional energy sources, the ability to deposit solvent, which must be used under carefully controlled con the chalcogenide-based absorber layers for the solar cells ditions (generally in an inert atmosphere Such as nitrogen or using liquid-based approaches is important. argon). Organic ligand molecules may also be toxic and dif 0003. A liquid-based approach exists which enables the ficult to remove from the resulting film, which may cause a deposition of kesterite Cu-Zn Sn—S Seabsorber layer problem in applications such as thin-film electronics (e.g., films. This liquid-based approach employs Zn-based nano impurities in the final film). particles and a hydrazine-based solution that contains Cu, Sn, 0007 An organoselenium approach introduces elemental and at least one of S and Se. See, for example, U.S. Patent Selenium through complicated and toxic organic chemical Application Publication No. 2011/0094557 A1 filed by Mitzi methodologies. In addition, the costs of Such reagents are et al., entitled “Method of Forming Semiconductor Film and quite high, which prevents their further application in large Photovoltaic Device Including the Film. (hereinafter “U.S. scale manufacturing. See, for example, D. Liotta, “New Orga Patent Application Publication No. 2011/0094557 A1), U.S. noselenium Methodology.” Acc. Chem. Res., 17, 28-34 Patent Application Publication No. 2011/0097496 A1, filed (1984) and A. J. Mukherjee, S. S. Zade, H. B. Singh, R. B. by Mitzi et al., entitled “Aqueous-Based Method of Forming Sunoj, “Organoselenium Chemistry: Role of Intramolecular Semiconductor Film and Photovoltaic Device Including the Interactions.” Chem. Rev., 110, 4357-4416 (2010). Film” (hereinafter “U.S. Patent Application Publication No. 0008. Other approaches use Se/NaBH or Se/NaS to 2011/0097496A1) and T. Todorov, K. Reuter, D. B. Mitzi, obtain a chalcogen solution. See, for example, D. L. Klay “High-Efficiency Solar Cell With Earth-Abundant Liquid man, T. S. Griffin, "Reaction of Selenium with Sodium Boro Processed Absorber.” Adv. Mater. 22, E156-E159 (2010). hydride in Protic Solvents. A Facile Method for the Introduc With this approach, thin-film solar cells with over 10% effi tion of Selenium into Organic Molecules' J. Am. Chem. Soc., ciency have been achieved, which are performance metrics 95, 197-199 (1973) (hereinafter “Klayman) (uses that have not yet been met using vacuum-based or any other Se/NaBH) and E. D. Kolb, R. A. Laudise, “The Solubility of processing techniques. Trigonal Se in NaS Solutions and the Hydrothermal Growth 0004 An analogous approach has been described for the of Se” J. Crystal Growth, 8, 191-196 (1971) (uses Se/NaS). preparation of high mobility metal chalcogenide films for These processes, however, introduce metal (i.e., Na) impuri thin-film transistor applications, which employs completely ties that may cause problems for electronics fabrications. dissolved metal chalcogenides with excess chalcogen Additionally, due to the inorganic nature of Sodium borohy included in the solution. See, for example, U.S. Pat. No. dride (NaBH), it is not easy to dissolve NaBH into some 6,875,661B2 issued to D. Mitzi, entitled “Solution Deposi solvents. For example, NaBH is insoluble in ethers and tet tion of Chalcogenide Films’ (hereinafter “U.S. Pat. No. rahydrofuran. Also due to the strong reactivity of borohydride 6,875,661 B2). In each of the above liquid-based techniques, (BHA), in cases involving solvents such as water and metha the ability to incorporate an excess amount of at least one of nol, NaBH will adversely react with the solvent. S and Se into the liquid is an important component of the 0009. In U.S. Pat.