New Routes to Binary and Ternary Semiconductors Potentially Important for Solar Cells and Thermoelectric Power Generation

Abstract

Metal sulfides comprise an important class of semiconducting materials and have potential uses in electronic, optical and optoelectronic applications, owing to their excellent physical and chemical properties. Binary antimony and bismuth sulfides, as well as their ternary sulfide counterparts, are highly useful in the wide range of applications, most notably, in solar cells and thermoelectrics. These semiconducting materials offer earth-abundant, low toxic and cheap alternatives for device fabrications, instead of commonly used highly toxic metals (such as Cd or Pb) or expensive scarce elements (such as Te, In). Several synthetic approaches are available for the preparation of these materials, however, the main issues are the formation of well-controlled products, in terms of stoichiometry, uniformity and crystallinity, as well as identification of the suitable precursor system required for their controlled synthesis. The use of sulfur-based single source precursors is often beneficial due to the presence of preformed bonds between metal and the sulfur atom, which allows better control over stoichiometry and phase. In this study, xanthate complexes of antimony(III), bismuth(III), indium(III), copper(II) and zinc(II) of the form M(S2COEt)n, as well as dithiocarbamate complexes of antimony(III) and copper(II) of the form M(S2CNEt2)n were synthesized, characterized and employed as molecular precursors for the preparation of binary, ternary and quaternary metal sulfide materials. This work is divided into six chapters, in which the first chapter provides a brief summary of the chalcogenide-based semiconducting materials and the different approaches for the synthesis of metal chalcogenide thin films and nanoparticles. This chapter also provides a comprehensive literature review of all the single source precursors used until the present for the preparation of antimony and bismuth chalcogenides, as well as their ternary chalcogenide materials. The second chapter describes the formation of ternary Bi2-2xSb2xS3 (0 ≤ x ≤ 1) solid solution in entire range with excellent stoichiometric control via solventless thermolysis using Bi(III) and Sb(III) ethylxanthates as molecular precursors. Structural analysis indicates the successful incorporation of antimony as a solid solution into the parent bismuth sulfide. Thin films were also deposited on glass substrates using spin coating and a fine band gap tuning was observed. In third chapter, the incorporation of indium into Bi2S3 and Sb2S3 via reactive melts routes were investigated. Sb(III), Bi(III) and In(III) complexes of ethylxanthates have been utilised as molecular precursors for the synthesis of M2-2xIn2xS3 (where M = Bi or Sb) in entire range with excellent stoichiometric control. In addition to the solventless synthesis, spin coating method was also used for the deposition of M2-2xIn2xS3 thin films and the effect of the chemical composition on band gap tuning was investigated. The fourth chapter describes the synthesis of phase-pure samples of two distinct phases of Cu-Sb-S, chalcostibite (CuSbS2) and tetrahedrite (Cu12Sb4S13), by the decomposition of mixture of Cu(II) and Sb(III) complexes of ethylxanthates. By tuning the molar ratio of copper and antimony xanthates, a single-phase of both chalcostibite and tetrahedrite were obtained. We have also explored the use of the Zn(II) and Bi(III) ethylxanthates for the formation of Zn-doped tetrahedrites Cu12-xZnxSb4S13 and Bi-doped tetrahedrites Cu12Sb4-xBixS13. Thin films were also deposited on glass substrates using dr-blade method and the effect of Zn and Bi doping on band gap energies was investigated. In fifth chapter, the deposition of ternary copper antimony sulfide thin films, by AACVD using Cu(II) and Sb(III) diethyldithiocarbamate complexes, was attempted with the aim to improve the chemical composition and quality of the deposited phase. Optimization of the synthetic conditions is needed in order to obtain single-phase ternary

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Paul O'Brien (Supervisor) & David Lewis (Supervisor)