| Summary: | 碩士 === 國立中興大學 === 電機工程學系所 === 107 === This paper uses plasma-enhanced chemical vapor deposition (PECVD) to adjust the hydrogen dilution ratio RH (H2/SiH4), process pressure (P), RF power (Prf) and pulse-wave conditions (ton/toff) to fabricate intrinsic hydrogenated amorphous silicon film (i-a-Si:H) with different energy gap (Eg), dielectric constant (ε), microstructure parameter (Rs*) and carrier lifetime (τeff). The influence of different intrinsic a-Si:H films on the performance of single- and double-intrinsic HIT solar cells were investigated.
The control ranges of hydrogen dilution ratio, plasma power, process pressure and pulse-wave conditions are 0%~2500%, 5~10W, 0.25~0.9 torr and 1ms/3ms~20ms/5ms respectively. The thickness (T), the refractive index (n), the extinction coefficient (k), and the dielectric constant (ε) of the film were analyzed by an ellipsometer (SE). Fourier transform infrared spectroscopy (FTIR) was used to analyze the microstructure parameters (Rs*). Quasi-static state photoconductivity (QSSPC) analyzes the minority carrier lifetime (τeff). Scanning electron microscopy (SEM) was used to analyze the surface state of single crystal silicon. High resolution transmission electron microscopy (HRTEM) analyzes defects between the film and substrate.
The Layer 1 intrinsic film with different process pressures prepared without hydrogen dilution ratio (RH=0) has a higher carrier lifetime and also has no formation of epitaxial layer (epi-layer) between the substrate and the film from HRTEM, representing that the Layer 1 film has better passivation effect on the n-c-Si substrate, but the Layer 1 film has lower imaginary peak of the dielectric constant (ε2: 22.1), poorer density, and higher microstructure parameters (Rs*: 56.69%), so that the ability to improve the heterojunction solar cell is limited. (Voc: 389mV, Jsc: 29.71mA/cm2, FF: 62.65%, η: 7.24%)
Layer 2 intrinsic films with different hydrogen dilution ratios at high process pressures (0.9 torr) have higher dielectric constant imaginary peaks (ε2: 26.1) and lower microstructure parameters (Rs*: 8.8%), the film has a high density, which can effectively reduce the recombination of the carrier in the film, but from the HRTEM observation, there is a 3~4 nm epitaxial layer between the substrate and the film, resulting in high interface defects between silicon substrate and film. The carrier is easily recombined at the interface, and the heterojunction solar cell cannot be effectively improved. (Voc: 401mV, Jsc: 30.52mA/cm2, FF: 64.25%, η: 7.85%)
Combining the above two films, this thesis uses a double-intrinsic layer method to suppress the formation of epitaxial layers, and has a high-density film to enhance the characteristics of heterojunction solar cells. First depositing a thin layer of Layer 1 on the silicon substrate surface can suppress the growth of the epitaxial layer. Next, depositing the low-defect and high-density Layer 2 can reduce the recombination of the carriers in the films. The method of double-intrinsic layer can reduce the leakage current and promote the shunt resistance, so that improve the performance of HIT solar cells. (Voc: 424mV, Jsc: 30.57mA/cm2, FF: 70.85%, η: 9.17%).
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