United States Patent (19) 11 Patent Number: 6,126,740 Schulz Et Al
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USOO6126740A United States Patent (19) 11 Patent Number: 6,126,740 Schulz et al. (45) Date of Patent: *Oct. 3, 2000 54 SOLUTION SYNTHESIS OF MIXED-METAL OTHER PUBLICATIONS CHALCOGENDENANOPARTICLES AND SPRAY DEPOSITION OF PRECURSOR “Preparation of Colloidal Semiconductor Solutions of MoS FILMS and WSea via Sonication,” M. Gutierrez, et al., Ultrasonics, vol. 27, (1989), pp. 259-261. (75) Inventors: Douglas L. Schulz, Denver; Calvin J. “Characterization of Solution-Synthesized CdTe and Curtis, Lakewood; David S. Ginley, HgTe.” M. Mullenborn, et al., Applied PhysicSA, (1993), pp. Evergreen, all of Colo. 317-321. “Quantum Size Effects in Zinc Oxide Nanoclusters Synthe 73) Assignee: Midwest Research Institute, Kansas sized by Reactive Sublimation.” Jackie Y. Ying, et al., City, Mo. Materials Research Society Symposium Proceedings, vol. Notice: This patent is Subject to a terminal dis 286, (1993), pp. 73–79. claimer. “Nanoparticle Precursor Route to Low-Temperature Spray Deposition of CdTe Thin Films,” Martin Pehnt, et al., Applied Phys. Lett., vol. 76, (1995), pp. 2176-2178. “Nanocrystalline Solutions of Precursor Solutions to the Appl. No.: 09/014,326 Spray Deposition of CdTe Thin Films,” Martin Pehnt, et al., Filed: Jan. 27, 1998 Mater. Res. Soc., (1995), pp. 461–467. “Solution Synthesis and Photoluminescence Studies of Related U.S. Application Data Small Crystallites of Cadmium Telluride,” Robert F. Jarvis, Continuation-in-part of application No. 08/536,348, Sep. 29, Jr., et al., Materials Research Society Symposium Proceed 1995, Pat. No. 5,711,803. ings, vol. 272, (1992), pp. 229-234. “Characterization of Solution-Synthesized CdTe and Int. Cl. ...................................................... C30B 1/02 HgTe.” M. Mullenborn, et al., Applied PhysicSA, (1993), pp. U.S. Cl. ....................... 117/4; 117/7; 117/9; 117/956; 317-321. 252/62.3 ZT; 252/62.3 GA “Photoluminescence in Spray-Pyrolyzed CdTe.” Bernard J. Field of Search ............................... 117/4, 7, 9,956; Feldman, Applied Physics Letter, vol. 9, (1981), pp. 252/62.3 ZT, 62.3 GA 703-705. References Cited Primary Examiner Robert Kunemund U.S. PATENT DOCUMENTS Attorney, Agent, or Firm-Ken Richardson; Paul J. White 4,225,408 9/1980 Barlow et al. ...................... 204/181 N 57 ABSTRACT 5,028,274 7/1991 Basol et al. ............................. 136/264 5,215,631 6/1993 Westfall ........... ... 204/64 R A colloidal Suspension comprising metal chalcogenide 5,262,357 11/1993 Alivisatos et al. ... 437/233 nanoparticles and a volatile capping agent. The colloidal 5,356,839 10/1994 Tuttle et al. .. ... 437/225 Suspension is made by reacting a metal Salt with a chalco 5,363,798 11/1994 Yoder ........................................ 117/89 genide Salt in an organic Solvent to precipitate a metal 5,436.204 7/1995 Albin et al. ... 437/225 chalcogenide, recovering the metal chalcogenide, and 5,441897 8/1995 Noufi et al. ................................. 437/5 admixing the metal chalcogenide with a volatile capping 5,470,910 11/1995 Spanhel et al. .. ... 524/785 agent. The colloidal Suspension is spray deposited onto a 5,491,114 2/1996 Goldstein ............. ... 437/233 5,537,000 7/1996 Alivisatos et al. ... ... 313/506 Substrate to produce a Semiconductor precursor film which 5,559,057 9/1996 Goldstein ............. ... 437/228 is Substantially free of impurities. 5,576,248 11/1996 Goldstein ..... ... 437/225 5,711,803 1/1998 Pehnt et al. ................................. 117/4 43 Claims, 2 Drawing Sheets U.S. Patent Oct. 3, 2000 Sheet 1 of 2 6,126,740 FIGURE U.S. Patent Oct. 3, 2000 Sheet 2 of 2 6,126,740 6,126,740 1 2 SOLUTION SYNTHESIS OF MIXED-METAL While the growth of single crystal CuInSea has been CHALCOGENDENANOPARTICLES AND studied, Such as in U.S. Pat. No. 4,652,332, issued to T. SPRAY DEPOSITION OF PRECURSOR Ciszek, the use of polycrystalline thin films is really more FILMS practical. Sputter depositing a ternary Single phase CuInSea layer, including the ability to determine the properties of the CROSS-REFERENCE TO OTHER thin film, Such as multilayer Structures, by varying the APPLICATIONS Sputter process parameters, is described in U.S. Pat. No. 4,818,357, issued to Case et al. However, the two fabrication This patent application is a continuation-in-part of U.S. methods of choice are: (1) Physical vapor deposition of the patent application Ser. No. 08/536,348, filed Sep.29, 1995, constituent elements, exemplified by the process disclosed and entitled “Preparation of a Semiconductor Thin Film,” in U.S. Pat. No. 5,141,564, issued to Chen et al., which is now U.S. Pat. No. 5,711,803. U.S. patent application Ser. generally used as a research tool; and (2) The Selenization of No. 08/535,981, filed Sep. 29, 1995. and entitled “Semicon Cu/In metal precursors by either HSe gas or Se vapor. The ductor Nanoparticle Colloids' is a copending application. Selenization technology generally exemplified by the pro CONTRACTUAL ORIGIN OF THE INVENTION 15 cesses described in U.S. Pat. No. 4,798,660, issued to Ermer et al., U.S. Pat. No. 4,915,745, issued to Pollack et al., and The United States Government has rights in this invention U.S. Pat. No. 5,045,409, issued to Eberspacher et al., is under Contract No. DE-AC36-83CH10O93 between the U.S. currently favored for manufacturing processes. However, Department of Energy and the National Renewable Energy thin films produced by the Selenization processes usually Laboratory, a Division of Midwest Research Institute. Suffer from macroscopic Spatial nonuniformities that BACKGROUND OF THE INVENTION degrade performance and yield, and reproducible consistent quality from run to run is difficult to obtain and unpredict 1... Field of the Invention able. Therefore, working with Cu(In,Ga)(Se,S) materials The present invention relates generally to preparation of has still been difficult, particularly when Scaling up. colloidal Suspensions of Semiconductor nanoparticles and, 25 U.S. Pat. No. 5,356,839, issued to Tuttle et al., U.S. Pat. more particularly, to preparing Stable colloidal Suspensions No. 5,441,897, issued to Noufi et al., and U.S. Pat. No. of mixed-metal chalcogenide nanoparticles and to the Spray 5,436,204, issued to Albin et al. describe methods for deposition of mixed-metal chalcogenide precursor films. producing high quality Cu(In,Ga)(Se,S) thin films using 2. Description of the Prior Art Vapor-phase recrystallization techniques. The fabrication Photovoltaic devices, used extensively in a myriad of processes described in these patents, each of which is applications, have generated considerable academic and assigned to the assignee of the present application, provide commercial interest in recent years. Photovoltaic devices improved performance and yield, and more reproducible (Solar cells) utilize the specific electronic properties of consistent quality than prior methods. For example, U.S. Semiconductors to convert the visible and near visible light Pat. No. 5,356,839 describes a process for fabricating Cu energy of the Sun into usable electrical energy. This conver 35 (In,Ga)Se films by initially forming a Cu-rich, phase Sion results from the absorption of radiant energy in the Separated compound mixture comprising Cu(In,Ga):CuSe Semiconductor materials which frees Some Valence on a Substrate, then converting the excess CuSe to Cu(In, electrons, thereby generating electron-hole pairs. The energy Ga)Se2 by exposing it to an activity of In and/or Ga, either required to generate electron-hole pairs in a Semiconductor in vapor In and/or Ga form or in solid (In,Ga)Se.. The material is referred to as the band gap energy, which in 40 characteristic of the resulting Cu(In,Ga)Se can be con general is the minimum energy needed to excite an electron trolled by the temperature. Higher temperatures, Such as from the valence band to the conduction band. 500-600° C., result in a nearly stoichiometric Cu(In,Ga) Semiconductor materials comprised of metals and Group Sea, whereas lower temperatures, such as 300-400 C., 16 elements (commonly referred to as chalcogens) are result in a more Cul-poor compound, Such as the Cu(In,Ga) important candidate materials for photovoltaic applications, 45 Se, phase. U.S. Pat. Nos. 5,441.897 and 5,436,204 describe Since many of these compounds (metal chalcogenides) have further modifications of the recrystallization process. optical band gap values well within the terrestrial Solar In addition to Selenium and Sulfur, another chalcogen, Spectra. Mixed-metal chalcogenide Semiconductors, Such as tellurium (Te), has also been used as a component in copper-indium-diselenide (CuInSe2). copper-gallium Semiconductor materials for thin-film Solar cells, usually in diselenide (CuCaSe2), and copper-indium-gallium 50 combination with Group 12 metals Such as cadmium (Cd) diselenide (CuIn , GaSea), all of which are Sometimes and mercury (Hg). One common method for making CdTe generically referred to as Cu(In,Ga)Sea, are of particular thin films is a Spray pyrolysis technique in which aqueous interest for photovoltaic device applications because of their Solutions of cadmium chloride and tellurium oxide are high Solar energy to electrical energy conversion efficien deposited on a Substrate at deposition temperatures between cies. Sulphur (S) can also be, and Sometimes is, Substituted 55 about 425° C. and 500° C. Like the Cu(In,Ga)(SeS). for Selenium, So the compound is Sometimes also referred to compounds, Te-based materials are typically coupled with a even more generically as Cu(In,Ga)(Se,S) to comprise all Second Semiconductor material of different conductivity of those possible combinations. The mixed-metal chalco type, Such as cadmium Sulfide (CdS). genides are typically coupled with a Second Semiconductor While the above-described metal chalcogenide semicon material of different conductivity type to produce a high 60 ductor films provide relatively high conversion efficiencies, efficiency heterojunction photovoltaic cell.