Excellent passivation properties of hydrogenated amorphous silicon oxide (a-SiOx:H) prepared by very high frequency plasma-enhanced chemical vapor deposition (VHF PECVD) at a low substrate temperature (170 °C) on crystalline and polycrystalline silicon (Si) wafers are reported. Films were characterized by ellipsometry, Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible (UV–vis) spectrophotometry, and dark-conductivity and photoconductivity measurements. A comparison of the results with those for different passivation layers such as hydrogenated amorphous silicon carbon nitride (a-SiCxNy:H), hydrogenated amorphous silicon nitride (a-SiNx:H), and hydrogenated amorphous silicon (a-Si:H) reveals their superiority as an excellent passivation layer for p-type crystalline Si as well as polycrystalline Si. A maximum effective lifetime of 400 µs was measured for 1–10 Ω cm, 380-µm-thick p-type c-Si using a micro-photocurrent decay (µ-PCD) system. Fixed charge density (Qf) was estimated by high-frequency (1 MHz) capacitance–voltage measurement using a metal–insulator–silicon structure (CV-MIS). The effect of annealing temperature on surface passivation in a nitrogen atmosphere was also studied.
Intrinsic hydrogenated amorphous silicon oxide (i-a-SiO:H) films deposited by very high frequency plasma-enhanced chemical vapor deposition (60 MHz VHF-PECVD) at a low substrate temperature of approximately 200 C were used as a front buffer layer in p-type hydrogenated microcrystalline silicon oxide/n-type crystalline silicon (p-mc-SiO:H/n-c-Si) heterojunction solar cells. We found that the oxygen concentration in the i-a-SiO:H buffer layer strongly affected the solar cell performance and that the short wavelength response in quantum efficiency (QE) was improved by oxygen addition. Employing a p-mc-SiO:H/i-a-SiO:H/n-Si [Czochralski (CZ), 200 mm, (100)]/i-a-Si:H/n-a-Si:H/Ag/Al configuration, we achieved an efficiency of 17.9% with V oc of 671 mV.
Wide-gap, high-conductivity p-type hydrogenated microcrystalline silicon oxide (p-mc-SiO:H) films deposited by very high frequency plasma-enhanced chemical vapor deposition (60 MHz VHF-PECVD) at a low substrate temperature of approximately [200 C] were used as window layers in n-type crystalline silicon (n-c-Si) heterojunction (HJ) solar cells. We investigated the effect of p-mc-SiO:H window layer thickness on HJ solar cells by changing deposition time and silane (SiH 4 ) flow rate. The effects of carbon dioxide flow rate on the p-mc-SiO:H window and i-a-SiO:H buffer layer were also studied. Employing a p-mc-SiO:H/i-a-SiO:H/n-c-Si [Czochralski (CZ), 200 mm, (100)]/ i-a-Si:H/n-a-Si:H configuration, we achieved an efficiency of 17.8% (active area efficiency) with an open-circuit voltage (V oc ) of 665 mV. The solar cells showed a spectral response of about 0.83 at a wavelength of 400 nm, which is higher than that of conventional HJ solar cells with amorphous silicon window layers.
Wide gap, highly conducting n-type hydrogenated microcrystalline silicon oxide (μc-SiO : H) films were prepared by very high frequency plasma enhanced chemical vapour deposition at a very low substrate temperature (170 °C) as an alternative to amorphous silicon (a-Si : H) for use as an emitter layer of heterojunction solar cells. The optoelectronic properties of n-μc-SiO : H films prepared for the emitter layer are dark conductivity = 0.51 S cm−1 at 20 nm thin film, activation energy = 23 meV and E04 = 2.3 eV. Czochralski-grown 380 µm thick p-type ⟨1 0 0⟩ oriented polished silicon wafers with a resistivity of 1–10 Ω cm were used for the fabrication of heterojunction solar cells. Photovoltaic parameters of the device were found to be Voc = 620 mV, Jsc = 32.1 mA cm−2, FF = 0.77, η = 15.32% (active area efficiency).
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