Study of thermoelectric properties of metal selenide based compounds

Abstract

This thesis aims to study thermoelectric (TE) power factor of thermally evaporated Ag2Se films near room temperature. Another objective of this work is Power factor enhancement and its stability in wide range of working temperature using a very conventional method of heat treatment. Chapter 1 includes basis of thermoelectricity and parameters on which thermoelectric performance depends. Thermoelectric materials have been classified into 3 categories on basis of their performance at different working temperatures: High temperature, mid temperature and low temperature TE materials. Recent literature review of some of the materials along with Ag2Se has been included. Chapter 2 involves sample preparation and heat treatment method to enhance TE performance. Film deposition set up, characterization techniques have been briefly explained. Apparatus of Van der pauw Hall measurement method and electrical characterization have been elucidated. Chapter 3 aims to enhance TE power factor of Ag2Se films. This is done by annealing the film in vacuum which improves film microstructure. Room temperature power factor of as-deposited and annealed Ag2Se films are compared. Annealing temperature of 210 °C has been optimized. Annealing at this temperature leads to preferential grain orientation of (013). Annealing duration of 1-1.5 hr at 210 °C has been found to yield best results. Main problem with pristine Ag2Se films is that, its power factor does not sustain at high working temperature of 90 °C. This issue is solved in Chapter 4 where three types of cations (Bi, Sb and Sn) are thermally diffused into the Ag2Se matrix independently. All the interdiffused films exhibit preferential grain orientation of (002) and (013). Power factor of all the cation diffused samples sustains below working temperature of 90 °C. Sn diffusion has also revealed comparable results and may act as substitute of Bi. Chapter 5 is devoted to summary and conclusions of the work presented in this thesis. newline