Preparation of Cu selenide and CuIn selenide particles with controlled morphology and structureAngshuman Pal , Ionel Halaciuga and Dan V Goia*, Chemistry & Biomolecular Science, Clarkson University *Email: goiadanv@clarkson.edu The interest in the preparation and characterization of semiconductor metal selenides has increased lately due to their potential applications in the fabrication of nanoscale electronic, optical, optelectronic, electrochemical devices1. Copper selenides are particularly important p-type semiconductors that have great potential in solar cells2, optical filters3, and as a supersonic material4. Copper selenides usually exists in form of copper(I) selenides (Cu2Se or Cu2-xSe) or copper(II) selenides (CuSe or Cu3Se2). Large-size, highly crystalline copper selenide particles are typically required for solar cells in order to result in a high mobility-life product5. In this study we describe the synthesis of such anisotropic crystalline stoichiometric CuSe and nonstoichiometric Cu2-xSe in polyols. The influence of the Cu-precursor, temperature, Cu to Se molar ratio and dispersing agent on particle morphology was investigated. The possibility to synthesize copper indium selenide using the same protocol was also explored.

References:1.a) Y. Qin, X. D. Wang, Z. L. Wang, Nature 2008, 451, 809. b) Z. L. Wang, Adv. Mater. 2000, 12, 1295. c) S. Frank, P. Poncharal, Z. L. Wang, W. A. de Heer, Science 1998, 280, 1744. d) X. Duan, Y. Huang, Y. Cui, J. Wang, C. M. Lieber, Nature 2001, 409, 66. e) Y. Cui, Q. Wei, H. Park, C. M. Lieber, Science 2001, 293, 1289. f) D. S. Wang, C. H. Hao, W. Zheng, Q. Peng, T. H. Wang, Z. M. Liao, D. P. Yu, Y. D. Li, Adv. Mater. 2008, 20, 2628. g) Y. W. Tan, X. Y. Xue, Q. Peng, H. Zhao, T. H. Wang, Y. D. Li, Nano Lett. 2007, 7, 3723.2. Hiroto, U. Jpn. Kokai Tokkyo Koho JP01298010, 1989. 3. Toyoji, H.; Hiroshi, Y. Jpn. Kokai Tokkyo Koho JP02173622, 1990.4. Korzhuev, A. A.; Khim, F. Obrab. Mater. 1991, 3, 131.5. V.M. GarcmHa, P.K. Nair, M.T.S. Nair J. Cryst. Growth, 1999, 203, 113.

Evaluation of different copper precursorsRecipe2 g Cu salt (nitrate, sulfate, acetate, carbonate)2 g H2SeO3250 cm3 PolyolReaction temperature: 170 °CReaction time: 2 hoursWash with DI-H2O and Ethanol

Copper precursor Cu [mol/dm3] Se [mol/dm3] Identified crystalline phaseCu(NO3)2·2.5H

2O 3.5 x 10-2 6.2 x 10-2 CuSe (hexagonal)CuSO4·5H2O 3.2 x 10-2 6.2 x 10-2 CuSe2 (orthorhombic)Cu(CH3CO2)2·H2O 4.0 x 10-2 6.2 x 10-2 CuSe (monoclinic)Cu2Se (cubic)Se (rhombohedra)Se6 (rhombohedra)

CuCO3·Cu(OH)2

7.2 x 10-2 6.2 x 10-2 CuSe (hexagonal)Cu7Se4 (cubic)Se (rhombohedra) We found that the CuSe (hexagonal) was formed in the case of Cu(NO3)2. However, noxes were formed as well (safety issues!). The carbonate is an attractive precursor because it does not contain stable counter ions (Cl-, NO3-, SO42-) and therefore results in better dispersed particles.

Effect of different parameters170 °C, 2 h 190 °C, 2 h

190 °C, 2 hCuSe / -CuSe

170 °C, 2 hCuSe / Cu7Se4 / Se

heating time

SEM & XRD

190 °C, 3 h190 °C, 2 h, Argon

Effect of dispersing agentD-Sorbitol PVP

PVA Daxad 11G

Dextran

Arabic gum

Crystalline stoichiometric (CuSe) and nonstoichiometric (Cu2-xSe) copper selenides were obtained with different dispersing agents in polyol. Morphological changes (flakes of 0.5 μm) were observed when polyvinylalcohol (PVA) was used as a dispersing agent at specific concentrations.

Effect of temperature along with PVP as a dispersing agentPVP (55K) 170 °C PVP (55K) 190 °C Cu2-xSe

PVP, 190 °CCuSe / Cu2-xSe

PVP, 170 °CCu2-xSePreparation of copper –indium- selenideRecipe

0.16 g In(NO3)30.45 g CuSe350 cm3 Tetraethylene GlycolReaction temperature: 190 oCReaction time: 14 hoursWash with DI-H2O and EthanolDrying for 6 hours at 85 oC

Cu-K Se-K In-L 38.69 54.15 7.16(Weight %)

Cu-K Se-K In-L32 40 6.96

Calculated valueExperimental valueEDS

Nanorod: d = 52 nm, l = (0.5 to1.8) μm

Effect of PVA concentration

CuSe / Cu2-xSe

PVA (50%)

PVA, 10 % PVA, 50 % PVA, 100 %

TEMXRD

ED

reduction

atmosphere

T & t: Complete conversion to CuSe. Atmosphere: size

Effect of concentration1X Con. ; 600 nm 2X Con. ; 500 nm 3X Con. ; 600 nm

Increased concentration did not cause a significant change in particle size