• Sanjay Tiwari

      Articles written in Bulletin of Materials Science

    • Influence of surface treatments on CdSe thin films in photoelectro-chemical solar energy conversion

      Shikha Mishra Sanjay Tiwari B P Chandra

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      Photovoltaic performance of semiconductor-liquid junction solar cell using electro-codeposited thin filmn-CdSe is found to improve significantly by proper surface treatments. The solid state parameters of annealed films are calculated and compared with those of unannealed film-based cells. Chemical etching is found to improve short circuit current and fill factor whereas photoelectrochemical etching technique improves the stability of photoanode in polysulphide electrolyte. Annealing promotes incipient fusion of small crystallites, thus reducing the grain boundaries which are known to act as recombination centres for minority carriers and trapping centre for majority carriers. The conversion efficiency and stability are found to improve by chemical etching of the semiconductor layer because chemical etching pins Fermi level of CdSe photoanode and promotes exchange current density.

    • Photoluminescence of gold-doped (Zn, Cd)S mixed phosphors

      Sanjay Tiwari Shikha Mishra B P Chandra

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      (Zn, Cd)S: Au, Cl mixed phosphors were prepared in nitrogen atmosphere with various concentrations of impurities. Photoluminescence (PL) spectra were obtained. The peak of the PL spectrum shifts towards longer-wavelength values with increasing replacement of zinc by cadmium in the host lattice. The PL efficiency was found to decrease with increasing. CdS content whereas lattice constants increased with increasing CdS concentration.

    • Preparation and characterization of gold doped (Zn, Cd)S mixed phosphors for mechano-optical transducers

      Sanjay Tiwari Shikha Tiwari B K Sahu B P Chandra

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      When mechanically excited, initially the ML intensity increases, attains a maximum value and then decreases with time. The total ML intensityIT initially increases with the impact velocityVo of piston and attains a saturation value for higher values ofVo and follows the relationIT=IToexp(−Vc/Vo) whereITo andVc are constants. The ML intensity is maximum for 20% CdS contents in the (Zn, Cd)S phosphors due to increase in hardness which may in turn increase the fracture stress and subsequently the piezoelectric field strength. The wavelength corresponding to the peak of both the ML and PL spectra shift towards longer wavelength with increasing CdS contents. Some models are discussed and it is concluded that the impulsive deformation of these phosphors may be due to piezoelectrification of newly created surfaces. The similarity of ML spectra with EL and PL spectra suggests that although the excitation processes are different, emission process is governed by the states of similar nature.

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