Dispersive and BEMA investigation on optical properties of photovoltaic thin films

Optical Absorption in Si:H Thin Films: Revisiting the Role of the Refractive Index and the Absorption Coefficient

“…As it can be expected absorption edges of µc-Si:H are obviously shifted to lower photon energies (i.e., higher wavelengths) in comparison to a-Si:H, so µc-Si:H absorbs red and near IR light better. Optical band gaps of these mixed-phase thin films based on several approaches were also reported [19,26].…”

“…To avoid the thicknessdependent deposition of Si:H, the thickness of the films was kept at approximately 400 nm. More details on the deposition conditions are in [19] where also prior studies on samples structure and microstructure were published. XRD, Raman scattering analysis and FTIR spectroscopy show that at dilutions R ≤ 30 the thin films consist of amorphous a-Si:H. At depositions with dilutions R > 30 material transforms to microcrystalline µc-Si:H. Volume fraction ratios of crystalline to amorphous phase p c /p a determined from XRD analysis are in Table 1.…”

“…The ratio of hydrogen bonded in dihydrides to the total bonded hydrogen is the microstructural factor. High values of this factor indicate the porosity of the samples [19] that was determined by the method described in [20].…”

“…Optical transmittance spectra in the wavelength range of (430 ÷ 1100) nm at nearly normal incidence were recorded by a Specord 210 spectrophotometer (Analytic Jena, Jena, Germany) and processed by optimization procedure based on genetic algorithm described in [19] to obtain the wavelength-dependent complex refractive index = + , where the refractive index n and the extinction coefficient k are the real and imaginary parts of . In the used optimization model the thin film was considered homogeneous with parallel smooth interfaces.…”

“…Thin films of a-Si:H, μc-Si:H as well as nanocrystalline Si:H under hydrogen incorporation are often reported as mixed-phase silicon [38,39] whereas the exact phase structure apparently influences the optical properties. The samples under study were also found to be mixed-phase materials containing microvoids inducing sample porosity [19].…”