Figure 9 TTe in the wavelength range of 400-2300 nm for IHfO:H films annealed at different temperatures.
As the annealing temperature increases, both the transmission and reflection spectra change significantly due to the change in refractive index caused by the rise in crystallinity (Figure S3).37 In order to eliminate the effect of reflection on transmission, the effective total transmittance (TTe) spectra are used instead of the transmission spectra to evaluate the optical properties of the IHfO:H films annealed at different temperatures,38 as shown in Figure 9. TTe is defined as \(\text{TTe}=\frac{T}{(1-R)}\), where T is the transmittance and R is the reflectance. When the annealing temperature is below or equal to 150 °C, the TTe of the IHfO:H films remains almost unchanged in the visible region while slightly increases in the NIR region. After the annealing temperature increases to 200 °C, the average TTe of the IHfO:H films increases from 88.54 % to 91.16 % in the visible region which can be related to better crystallization with less defects.39 Meanwhile, the average TTe significantly increased from 77.14 % to 95.61 % in the NIR region. According to the Drude model, FCA is proportional to carrier concentration.34 Thereby, the IHfO:H films annealed at temperature above 200 °C behave higher transmittance as they have lower carrier concentration as shown in Figure 7.
Overall, the post-annealing treatment shows a significant impact on the crystallinity, the electrical properties, and the optical transmission of the IHfO:H films. Considering the above opto-electronic characteristics comprehensively, the appropriate annealing temperature is about 200 °C which is within the temperature tolerance range of the SHJ solar cells.
3.3 Application of the IHfO:H films on SHJ solar cells