Tin-selenide for thermoelectric and opto-electronic applications

With recent advancement in technology miniaturing device is required to open the aspect of the thin film research area. Materials can be used to detect the presence of the photons and to convert the photon's energy into electrical energy also. Detection of photons opens a new door to the applications like optical communication, weather forecasting, automatic sensors in defense sectors, spectroscopy, imaging in the medical field, etc. As far as concerned with the conversion of the photons, it strikes to mind that the material can be applied in solar cells. As renewable energy resources are timely needed, solar energy is one of the cheapest resources to be harnessed. Harnessing solar energy requires efficient materials (having a suitable band gap range corresponding to the photon energy) that can convert solar energy (photons) into electrical energy. It is one side of the coin, as whatever energy is consumed in daily life based on non-renewable source engines is wasted in heat. This wastage makes an economic loss and increases the rate of depletion of natural resources. On other hand, 87 % of the energy of the world comes from fossil fuels. Out of that 70% of the energy is wasted mainly in the form of heat. This fact has forced scientists to focus on improving the sustainability of the harnessed energy which may extend the reserve depletion time of the natural resources as well. By converting waste heat into useful energy, one might substantially reduce the demand for energy in the world. Thermoelectric materials can be deployed for this purpose. Meanwhile metal chalcogenides are most recently focused material among the researchers due to their optimum band gap, high absorption coefficient. Easy tunability of band gap, less covalent nature of bond due to low electronegativity makes metal chalcogenides a better choice of thermoelectric and opto-electronic material. The aim of this research is to explore the thermoelectric and optoelectronic (viz. photoconductive and photovoltaic performance of SnSe film aspect using an industrially viable technique thermal evaporation. In this work pure polycrystalline SnSe is synthesized by solid state reaction and as obtained crushed powder is used to deposit film on different substrates. Chapter 1 introduces the background, motivations, literature survey and objectives of the research in this thesis. The research scopes of the thesis are defined. The identified research gaps are presented, and research questions are raised. The expected research outcomes/deliverables are demonstrated. Chapter 2 illustrates the methodology of the research being carried out on the SnSe. The methods adopted for the synthesis and deposition of SnSe and characterizations of the SnSe film, and optoelectronic and thermoelectric parameters are illustrated. Chapter 3 is based on the four published works on the photoconductive (PC) application of SnSe. Photoconductive properties of the SnSe film on the glass substrate, open air annealing effect on the PC performance of SnSe with different time and temperature, and finally PC performance of the SnSe/Sb2Se3 heterostructure for self-powered and flexible device are presented. Chapter 4 is based on the two published works on photovoltaic (PV) application of SnSe. Theoretical approach is presented for the high-efficient SnSe bases solar cell with CdS as an absorber layer. In the second part the photovoltaic performance of an annealed SnSe is presented to naturally grow in a solar cell structure. Experimental and theoretical approaches are presented for the annealed device. Chapter 5 tries to solve the problems faced by SnSe in thermoelectric applications. A protective coating of Si suggested by Li et al. is used to protect the SnSe and to prevent the possible degrading of the performance of the device at higher temperatures. Also, a published work on the thermoelectric performance of the SnSe and Bi composite made by the thermal evaporation method is presented. Chapter 6 concludes the thesis and suggests the future direction of the research in the thesis.