Synthesis and characterization of In2S3: Na thin films prepared by vacuum thermal evaporation technique for photovoltaic applications

摘要

In2S3 thin films containing different quantities of sodium have been synthesized by coevaporation of sodium and In2S3 powder from separate sources using vacuum thermal evaporation method. Films were deposited on ordinary glass at 240 degrees C. The process of incorporation of sodium was studied as function of at.% Na. Films have been characterised by means of X-ray diffraction, SEM, EDAX and spectrophotometry. X-ray diffraction analysis confirmed the initial amorphous nature of deposited layers and revealed the formation of In2S3 as function of annealing layers containing sodium in nitrogen at 300 degrees C for 2 h. Energy Dispersive X-ray Analysis (EDAX) revealed the composition of the films as a function of the sodium incorporation. Surface Electron Microscopy showed that these films were granular and homogenous. The films have an n-type electrical conductivity and their optical direct band gap can be managed between 2.20 and 2.45 eV by controlling their sodium content. The variation of parameters for as-deposited and annealed films has been studied within x <= 4 at.% solid solution composition. Thin layers with homogeneous surfaces, direct band gap energy (E-g) of about 2.45 eV for 4 at.% Na and 0.9 mu m-thick have been achieved.