N-layer engineering on the performance of HIT solar cells

• Main Authors: Xiang-Jun Xu, 徐祥鈞
• Other Authors: 江雨龍
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/6a87gh

碩士 === 國立中興大學 === 光電工程研究所 === 106 === In this thesis, n-type hydrogenated amorphous silicon (a-Si:H) films with different band gaps (Eg), activity energy (Ea) and dark conductivity () were fabricated by modulated plasma power, pressure, RPH3 (PH3(1% in H2)/SiH4) and hydrogen dilution RH2 (H2/SiH4) ratio by plasma-enhanced chemical vapor deposition. The n-type a-Si:H films were deposited on p-type single crystalline silicon substrates for single-side heterojunction with intrinsic thin films (HIT) solar cells. The influence of different n-type a-Si:H films on the performance of HIT solar cells were investigated. The conditions of plasma power, pressure, RPH3 and RH2 are controlled at 4 and 12W, 0.5 torr and 1 torr, 3% to 125% and 3 to 20, respectively. The optical properties of the n-type a-Si:H films were analyzed by an ellipsometry to determine the thickness, energy gap, refractive index, extinction coefficient and dielectric constant. Dark current was used to analyze the dark conductivity and activity energy of the films. The n-type film fabricated at 4W low plasma power and 0.5 torr low pressure has higher band gap and activity energy, indicating lower doping concentration. High dark conductivity, refractive index, extinction coefficient and dielectric constant of the film reveals the film has a more-dense structure. The n-type film fabricated at 12 W high plasma power and 1.0 torr high pressure has higher band gap and activity energy, indicating higher doping concentration. Lower dark conductivity, refractive index, extinction coefficient and dielectric constant of the film reveals the film is less-dense structure. The changes of I-V characteristics of heterojunction solar cells are investigated in terms of the thickness of n layer (10 nm~30 nm). Increasing the thickness of the n layer increases the open circuit voltage and the fill factor of the solar cells, thereby improving the efficiency. High plasma power with high pressure and low plasma power with low pressure were used to deposite two types of n-type a-Si:H films of low band gap (1.62 eV) with low dark conductivity (2.35E-03 S/cm) and high band gap (1.68 eV) with high dark conductivity (9.57E-03 S/cm), respectively. Comparison of HIT solar cells with these two types of n-type films, high band gap (1.68 eV) n-type film compared to the low band gap (1.62 eV) n-type film could increase the built-in electric field and to increase the open circuit voltage from 0.376 V to 0.421 V. High dark conductivity (9.57E-03 S/cm) and high-dense structure n-type film compared to the low dark conductivity (2.35E-03 S/cm) and the low-dense structure n-type film could reduce the series resistance of the solar cell and increase the fill factor from 51.23% to 57.41%. The short-circuit current was slightly reduced from 29.92 mA/cm2 to 29.36 mA/cm2. Therefore the solar cells conversion efficiency was increased from 5.78 to 7.10%. Higher band gap and dark conductivity of the n-type hydrogenated amorphous silicon film optimizes the heterojunction solar cell and improves conversion efficiency.