On KCN treatment effects on optical properties of Si-based bilayers

In this paper we report results from optical transmittance spectroscopy complemented with data from Raman scattering measurements to determine optical properties of two series of silicon based bilayers deposited by PECVD on glass substrate (intrinsic a-Si:H/p-type a-SiC:H and n-type mc-Si:H/intrinsic a-Si:H). These samples represent segments of common p-i-n thin film amorphous silicon solar cells with intrinsic hydrogenated silicon (a-Si:H) as the solar absorber. The members of the series differ by the KCN treatment conditions. Dispersive and absorptive optical properties – refractive indices, absorption coefficients and optical band gaps were determined from transmittance spectra. Each bilayer was considered as one effective thin film the optical properties of which can be regarded as effective optical properties of the bilayer structure. After KCN treatments refractive indices were modified probably due to the structural changes of bilayers. Moreover the effect of the solvent used in KCN solutions was recognized. Optical band gaps calculated either by the Tauc procedure or determined as iso-absorption levels were found to be only slightly KCN treatment dependent.