Enhanced thermopower in (013)-oriented silver selenide films produced by thermal annealing

Abstract

Nanocrystalline thin films of thermoelectric compound Ag2Se (AS) were deposited on the glass substrate kept at room temperature by thermal evaporation technique. Deposited films were annealed in vacuum of 2 × 10–5 mbar at 90 °C, 120 °C, 150 °C, 180 °C and 210 °C for 1 h. A sudden change in crystal orientation from (121) to (013) was observed as annealing temperature was increased to 210 °C. Seebeck coefficient for (013) oriented film was also found to be − 114.6 μV/K at room temperature compared to − 62.3 μV/K for as-deposited film. Formation of silver segregates in the film was observed where variation of size of silver grains on annealing played a crucial role in optimising Seebeck coefficient. Energy filtering effect by silver grains in combination to (013) orientation of silver selenide crystals was inferred as a reason for enhancement of Seebeck coefficient. Room temperature value of power factor was optimised at annealing temperature of 120 °C (AS-120) which was calculated to be 755.0 μW/mK2 and was also found to be comparable to that of film annealed at 210 °C (AS-210) i.e., 705.6 μW/mK2. Unlike AS-120, power factor value of AS-210 was due to considerable value Seebeck coefficient.