Effective Ag Doping by He-Ne Laser Exposure to Improve the Electrical and the Optical Properties of CdTe Thin Films for Heterostructured Thin Film Solar Cells

Effective Ag Doping by He-Ne Laser Exposure to Improve the Electrical and the Optical Properties of CdTe Thin Films for Heterostructured Thin Film Solar Cells

The Cadmium telluride (CdTe) thin film solar cell is one of the strongest candidates due to the optimum band gap energy (about 1.4 eV) for solar energy absorption, high light absorption capability and lower cost requirements for solar cell production. However, the maximum efficiency of CdTe thin film solar cell still remains just 16.5% despite its excellent absorption coefficient; i.e., the electrical properties of CdTe thin film, including the resistivity, must be improved to enhance the energy conversion efficiency. Silver (Ag) was doped by helium-neon (He-Ne) laser (632.8 nm) exposure into the sputtering deposited <I>p</I>-type CdTe thin films. The Ag-doped CdTe thin films reduced the resistivity from 2.97 × 10<SUP>4</SUP> Ω-cm to the order of 5.16 × 10<SUP>-2</SUP> Ω-cm. The carrier concentration of CdTe thin films increased to 1.6 × 10<SUP>18</SUP> cm<SUP>-3</SUP> at 15 minutes of exposure time in the He-Ne laser. The average absorbance value of CdTe thin films improved from 1.81 to 3.01 by the doping of Ag due to impurity-scattering. These improved properties would contribute to the efficiency of the photovoltaic effects of the photogenerated charged carriers. The methodology in this study was very simple and effective to dope the multilayered thin film solar cell with a relatively short process time, no wet-process, and selective treatment.

The Cadmium telluride (CdTe) thin film solar cell is one of the strongest candidates due to the optimum band gap energy (about 1.4 eV) for solar energy absorption, high light absorption capability and lower cost requirements for solar cell production. However, the maximum efficiency of CdTe thin film solar cell still remains just 16.5% despite its excellent absorption coefficient; i.e., the electrical properties of CdTe thin film, including the resistivity, must be improved to enhance the energy conversion efficiency. Silver (Ag) was doped by helium-neon (He-Ne) laser (632.8 nm) exposure into the sputtering deposited <I>p</I>-type CdTe thin films. The Ag-doped CdTe thin films reduced the resistivity from 2.97 × 10<SUP>4</SUP> Ω-cm to the order of 5.16 × 10<SUP>-2</SUP> Ω-cm. The carrier concentration of CdTe thin films increased to 1.6 × 10<SUP>18</SUP> cm<SUP>-3</SUP> at 15 minutes of exposure time in the He-Ne laser. The average absorbance value of CdTe thin films improved from 1.81 to 3.01 by the doping of Ag due to impurity-scattering. These improved properties would contribute to the efficiency of the photovoltaic effects of the photogenerated charged carriers. The methodology in this study was very simple and effective to dope the multilayered thin film solar cell with a relatively short process time, no wet-process, and selective treatment.