Development of metal chalcogenide precursors for use in chemical vapour deposition (CVD) and colloidal nano particle synthesis

Non-oxide group IV metal chalcogenides have attracted considerable attention due to prospective applications in materials chemistry. These materials have been reported to have applications in sensors and laser materials, thin film polarizers, thermoelectric devices (e.g. Joseph Heremans and colleagues have shown PbTe is a potential material for high temperature thermoelectric energy generation), photoelectrochemical (PEC) solar cells (e.g. SnSe used to suppress photo corrosion of PEC), thin film photo voltaics (e.g. Copper Zinc Tin Selenide/Sulphide) as well as cathode materials for lithium ion batteries due to the anisotropic crystal structures. One governing property of the materials is that they act as semiconductors with medium and small band gaps (0.10 – 1.50 eV).
The low band gap properties of PbSe have been utilised in the construction of a fission-sensitized solar cell (FSSC), which have the theoretical potential to exceed the Shockley–Queisser limit for a single heterojunction solar cell. Bruno Ehrler and colleagues have demonstrated by constructing a Pentacene/PbSe nanocrystal interface the singlet to triplet fission in high band gap pentacene can be detected via the PbSe interface. There is a lot of optimism surrounding FSSC and there is considerable focus on nano-crystal size, morphology and monodispersity of the metal chalcogenide nano crystals in order to improve FSSC device performance and optimise their band gap. Therefore the design of precursors for these materials is paramount.
The poster will present our latest development in the synthesis and characterisation of a range of novel tin chalcogenide complexes that are potential precursors in the production of thin films via CVD. We have also shown that the precursors can be used for the synthesis of nanoparticle with various morphologies and optoelectronic properties.
We have made a range of tin chalcogenide complexes, one group of organometallic compounds we synthesised exploited the insertion reaction of R-carbodiimide into bis-dimethylamide tin(II) to produce a number of confined Tin(II) complexes (where R= di-cyclohexyl,-isopropyl and -4-methylphenyl), with an available lone pair of electron orbitals for further reactions with chalcogenide compounds to form Sn(IV)chalcogenide complexes (Figure 1).
With relevant structural, physical data, such as melting points and thermogravimetric analysis and deposition studies, we have developed promising novel precursors for aerosol assisted CVD to produce thin films of SnTe, SnSe, SnS and SnO with various stoichiometric ratios (1:1, 1:2 and 1:4).
In addition I have synthesised and characterised a range of tin chalcogenide nano crystals (Figure 2). We investigated the effects of various synthesis parameters and types precursors used during nano crystal synthesis, which will make contributions to the popular research of nanoengineering materials. In addition we hope to test the optoelectric properties of the nano particles by constructing and using an open circuit Au lithographed device (with 1m wide closed circuit channels), from which we can determine the induced photocurrent. In addition we will present the reflectance spectra to indirectly determine the variation in band gaps of the various particles.
We also aim to present the improved synthesis method and recent structural characterisation of selenoisocyanate compounds, which have interesting reactivity with group IV metals (Figure 3). We have shown as they are isoelectric to CO2 they can act as metal insertion ligands. In addition, due to the relatively weak C=Se bonding these compounds also act as selenium oxidising agents by providing a monomeric sources of selenium, to metal centres. Furthermore, we demonstrated that selenoisocyanates have desirable physical properties, acting as soluble sources of selenium, where volatile isocyanides can be reused or readily evacuated, which is an improvement from using selenium powder and phosphine base selenium precursors.