[21a-B12-1~8] 16.3 Bulk, thin-film and other silicon-based solar cells

▼ [21a-B12-5] Investigation of correlation between the conductivity increasing of SiN_x thin films by UV light and potential induced degradation

〇(D)Dong Chung Nguyen¹, Yasuaki Ishikawa¹, Sachiko Jonai^1,2, Kyotaro Nakamura³, Atsushi Masuda², Yukiharu Uraoka¹ (1.NAIST, 2.AIST, 3.TTI)

Keywords:PID, Silicon photovoltaics, Silicon nitride

Irradiating UV light on p-type crystalline Si (c-Si) solar cells during potential induced degradation (PID) tests can delay the degradation of the solar cell performances. A highly conductive silicon nitride (SiN_x) layer has a significant influence on the PID resistance of p-type c-Si solar cells, suggesting an investigation of the change of the SiN_x properties under UV light irradiation is necessary. This work studied conductivity change in SiN_x thin films under the UV light irradiation. Three SiN_x thin film samples with different refractive indexes (n) were prepared by plasma-enhanced chemical vapor deposition (PE-CVD) method. Band-gap of SiN_x thin films estimated based on the absorption edge method is 3.56 eV (348 nm), 3.18 eV (390 nm) and 2.97 eV (418 nm) corresponding to refractive indexes of 1.95, 2.12, and 2.20 estimated at 600-nm wavelength, respectively. The conductivity of the SiN_x thin films was measured by a two-probe measurement in a vacuum chamber with a pressure of 2.3 x 10^-2 Pa with several conditions: an applied voltage of 40 V, light irradiation of similar photon flux of 9.26 x 10¹⁴ photon/cm²s at the wavelengths of 300 nm, 370 nm, 390 nm, 460 nm and 500 nm. Increasing of conductivity and photosensitivity of SiN_x thin films under light irradiation depend on their refractive indexes and are limited by their band-gap. These results are in good agreement with previous results using SiN_x thin films prepared by catalytic chemical vapor deposition method reported by our group. We presume that these increasing of photosensitivity by UV light irradiation is responsible for PID delay effect.