The peak at approximately 510 cm-1 is originating from Si-QDs. The Gaussian curve is indicated by green dashed line. As the CO2/MMS flow rate ratio increases, the intensity of the peak from Si-QDs becomes weaker compared with the peak from a-Si phase. This indicates that the crystallization of Si-QDs in the silicon-rich layers is prevented by the oxygen-incorporation, and the crystallization temperature of nanocrystalline silicon phase becomes higher [31]. Figure 3 The Raman spectra of the Si-QDSLs with several CO 2 /MMS flow rate ratios. (a) CO2MMS = 0. (b) CO2MMS = 0.3. (c) CO2MMS = 1.5. (d) CO2MMS = 3. The absorption coefficient was estimated from the measurements of transmittance and reflectance. The
absorption
coefficients of the Si-QDSLs with the CO2/MMS flow rate ratios of 0, 0.3, 1.5, and 3.0 are shown in Figure 4. For both Si-QDSLs with the CO2/MMS flow rate ratios of 0 and 0.3, the absorption enhancement was observed selleck chemical below the photon energy of 2.0 eV. selleck compound Moreover, the absorption enhancement becomes weaker as the CO2/MMS flow rate ratio increases. This tendency corresponds to that of the intensity of the peak originating from Si-QDs in the Raman scattering spectrum. Therefore, one can conclude that the absorption enhancement is due to the increment of the nanocrystalline silicon phase. Moreover, the absorption edge was 4SC-202 mw estimated by the Tauc model [32]. The absorption edges of the Si-QDSLs with the CO2/MMS flow rate ratios of 0 and 0.3 were estimated at 1.48 and 1.56 eV, respectively. These values are similar to the optical gap of 5-nm-diameter Si-QDs in an a-SiC matrix measured by photoluminescence spectrum [2]. On the other hand, the absorption edges of the Si-QDSLs with the CO2/MMS flow rate ratios of 1.5 and 3.0 were estimated at approximately 1.70 eV, which corresponds to the optical gap of a-Si. Figure 4 The absorption coefficients of the Si-QDSLs with several CO 2 /MMS flow rate ratios. These
results indicate that the CO2/MMS flow rate ratio should be below approximately 0.3 to form Si-QDs in the silicon-rich layers. According to the [22], the CO2/MMS flow rate ratio should be higher than 0.3 to suppress the crystallization of a-SiC phase in the a-Si1 – x – y C x O y barrier layers and the increment of the dark conductivity for the annealing Montelukast Sodium temperature of 900°C. Although there is a trade-off between the promotion of the crystallization of Si-QDs and the suppression of the crystallization of a-SiC phase, the CO2/MMS flow rate ratio of approximately 0.3 or the oxygen concentration of approximately 25 at.% is one of the optimal conditions. Therefore, the CO2/MMS flow rate ratio of 0.3 is adopted for the solar cell fabrication in this study. I-V characteristics of the fabricated solar cells The cross-sectional TEM images of the fabricated solar cell are shown in Figure 5. Figure 5a shows the image of the whole region of the solar cell.