The use of Soluble Metal-Polyselenide Complexes as Precursors to Binary and Ternary Solid Metal Selenides
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THE USE OF SOLUBLE METAL-POLYSELENIDE COMPLEXES AS PRECURSORS TO BINARY AND TERNARY SOLID METAL SELENIDES S. Dhingra and M. G. Kanatzidis* Department of Chemistry and Center for FundamentalMaterials Research, Michigan State University, EastLansing MI 48824 USA
ABSTRACT The use of several soluble metal polychalcogenides to prepare solid state materials is presented. Thermal gravimetric analysis (TGA) data, under inert atmosphere, of the molecular compounds (Ph4P)2[Cd(Se4)2], (Ph4P)4[Cu2Sel4], (Ph4P)2[Cu4SeI2], (Ph4P)4[1n 2 Se21 ] and (Et4N) 3[M3 Se15], (M=In, TI), show that the corresponding binary solid state compounds are formed as single phases at temperatures as low as 530 (C. We have grown films of CdSe, Cu2. xSe, f0-In2Se3, TISe and CuInSe2 using these complexes as precursors. The films were prepared by pyrolysis of green precursor films, cast from DMF solutions. CuInSe2 was prepared by co-thermolysis of Cu/Sex and In/Sex complexes. The chemical, X-ray, spectroscopic and electron microscopic characterization of these molecular precursor-derived films as well as their charge transport characterization is reported.
INTRODUCTION Compared to the extensive investigations into the chemistry of molecular precursor materials for the synthesis of metal oxide ceramics and semiconductors, little work has been carried out in the area of chalcogenide solid state materials, particularly involving the heavier chalcogens. Of the molecular chalcogenides, sulfides are the most studied. The work on sulfides has concentrated on volatile species primarily for metal-organic chemical vapor deposition (MOCVD) work (e.g synthesis of ZnS and CdS). 1 The volatility of molecular metalchalcogenides decreases rapidly from S to Te. The task of producing stable volatile M/Q (Q=Se,Te) compounds for MOCVD is extremely difficult. On the contrary it considerably easier to synthesize pure non-volatile complexes of metal-chalcogenides, and thus it would be highly desirable if methods were developed to fabricate chalcogenide films of comparable quality to those obtained by MOCVD. The molecular chalcogenide chemistry we have been developing in our laboratory, places us in an advantageous position to explore the possibilities for the synthesis and film fabrication of solid state binary or ternary sulfides, selenides and tellurides from the corresponding molecular complexes. Solid state chalcogenides enjoy such practical applications as IR detection and imaging 2 , electroluminescent devices 2 ,3 , optoelectronics 4 , solar cells 5 and high energy density rechargeable batteries. 6 Todate, most of these materials are made at temperatures greater than 700 OC. Here we report our preliminary results on the use of soluble metal/polyselenides as precursors to prepare films of important solid state binary and ternary selenides. EXPERIMENTAL SECTION The precursor polyselenide complexes were prepared as described previously. 7 ,8 The Xray powder diffraction patterns of all materials were recorded with a Phillips XRG-3000 computer controlled powder diffractom
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