NH4Cl treatment on electron-beam evaporated CdX (x = Te, Se) thin films for absorber layer applications

Abstract

To augment the performance of Cd-based solar cells, the post-chloride treatment is an imperative processing step. Therefore, in this study, the influence of low-cost non-carcinogenic and ecofriendly NH4Cl thermal activation to the physical properties of electron beam evaporated CdX (X=Te, Se) thin films having thickness 800 nm is reported. The structural studies of NH4Cl activated CdX thin films reveal that both the CdSe and CdTe films exhibited polycrystalline nature with (111) and (211) preferred planes of cubic phase respectively. Also, the maximum grain growth is observed at 320 °C annealing for both types of films. The optical absorbance for CdTe system is found high vis-a-vis to CdSe system in the visible region. The transmittance is found minimum and having a wavy shape for CdSe films. The estimated direct band gap of CdSe and CdTe films (for 320 °C annealed films) is observed close to the standard value i.e. 1.47 eV for CdTe and 1.77 eV for CdSe films. The I-V characteristics are linear for both types of the films with varied conductivity. The surface morphology reveals uniform deposition of films and the elemental analysis assured the deposition of CdSe films as well as Cl-treatment. On the basis of the optimized results like higher crystallinity, suitable morphology, ohmic nature and optimal bandgap, the CdX films processed at 320 °C have potential candidature to use as absorber layer in the fabrication of efficient Cd-based solar cells.