An evolution to Cu concentration on ZnTe thin films: functionality as interface layer to CdTe solar cells

The ZnTe thin films are typically employed as back contact interface layer in between CdTe absorber and metal electrode in superstrate device architecture for reducing open circuit voltage loss and enhancing device performance. Copper (Cu) is considered as a vital dopant for catalyzing recrystallization and facilitating inter-diffusion between CdTe and ZnTe layers. Hence, the present research work deals with evolution of Cu doping concentration to the physical properties of ZnTe:Cu films in view of interface layer applications to CdTe solar cells wherein Cu content is taken as 1%, 3%, and 5%. The polycrystalline ZnTe:Cu thin films with thickness 200 nm were developed via resistive heating based thermal evaporation method on glass and ITO substrates followed by annealing in air ambient at 300 degrees C temperature for 1 h. The structural investigation revealed to (103) orientation as dominant reflection corresponding to zinc blende cubic phased structure where crystallite size is improved within range 36-53 nm. The optical energy band gap of the prepared ZnTe:Cu layers is attained within 2.34-2.57 eV range with varying Cu concentration and PL spectra depicted presence of two peaks centered at 351 nm and 451 nm wherein ZnTe:Cu 5% films showed better PL intensity. The I-V characteristics disclosed establishment of Ohmic contacts between the films surface and TCO layers concerned. The AFM micrographs of ZnTe:Cu films depicted hill-like topographies where hill height and intensity are enhanced for the ZnTe:Cu 5% films. The findings explicitly demonstrated that concentration of Cu dopant has radically persuaded physical properties and the ZnTe:Cu 5% films may be implicated as back contact interface layer to the device architecture concerned.