Impact of Bi doping on CdTe thin films: Thermal annealing evolution of physical properties for solar cell absorber layer applications

摘要

To mitigate probability of instability and device degradation associated with traditional Cu doping and to tune required band gap as well as to reduce open circuit voltage loss to solar cell device, a study on evolution to the physical properties of Bi-doped CdTe films is reported. Thin films of CdTe:Bi 2% alloy are developed employing electron-beam deposition followed by air annealing. Structural studies reveal that films have preferred crystal growth along (111) plane and with annealing, films turned out to be polycrystalline. Absorbance of films is found to be affected with annealing where 450 degrees C annealed films show maximum absorbance. The current-voltage measurements show linear relationship reveal to ohmic contacts between the films and transparent conducing oxide substrate and conductivity is observed to be varied with annealing. The atomic force microscopy study indicates an increase in surface roughness with annealing (except for 300 degrees C). Our findings warrant that the optimized physical properties of CdTe:Bi 2% films annealed at 450 degrees C may play important role to enhance the solar cell device performance concerned.