The substitutional B-interstitial O-related defects induced under an illumination, specific to B-doped Czochralski-grown silicon (Cz-Si), results in a solar cell efficiency loss of up to 3%. For a fundamental interpretation, the relationship between the solar cell performance and the minority-carrier lifetime degradation, and influence of the illumination conditions were investigated. A simulation of the cell performance degradation clearly represented that the degradation was explained as a result of the carrier diffusion length degradation. From a spectroscopic illumination investigation, the degradation was found to be independent of the stress-light wavelength. A blue light illumination on a solar cell resulted in the red response degradation, suggesting that the injected carriers activated the defect in the bulk. However, the correlation between carrier injection level and the cell performance decay time was nonlinear. The observed decay times were almost independent of the illumination intensity in the range of 1 to 100 mW/cm2. This trend appeared more significantly on cells with a higher base resistivity. From the experimental results, the role of excess carriers in the defect activation was discussed.

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The rapid initial degradation of Czochralski-grown silicon (Cz-Si) solar cell performance has been investigated. The initial rapid degradation occurs at the beginning of the degradation process and is followed by a second slower degradation. The surface effect due to interface state degradation between the passivation layer and the Si substrate was investigated on several kinds of Cz-and float zone Si (FZ-Si) wafers. Carrier lifetime degradation induced by an illumination for 30 s was observed on every Cz-Si wafer, but no degradation was observed on FZ-Si wafers. Moreover, only the decrease of IR response of a cell was observed as a result of the initial degradation. The results suggest that the degradation occurs in the bulk. The magnitude and decay time of the degradation appear to depend on the wafer resistivity. Defects very similar to boron-oxygen complexes specific to Cz-Si were considered to be responsible. The distinctly small activation energy of 0.19 eV was obtained for the initial degradation, which suggests a fundamentally different defect reaction process. The activation energy of 1.6 eV for the defect annihilation process was obtained for both defects as well.

Recent research on light degradation of crystalline Si materials and solar cells is reviewed. The first paper on the issue was published in 1973 when efficiency of solar cells using 1 Ω cm, B‐doped CZ wafers degraded under illumination and recovered by annealing at a low temperature of around 200°C. In the 1990's, several studies have been performed to investigate the mechanism of the light degradation and also to provide practical solutions to suppress the degradation. Numerous experiments have been carried out regarding the effects of impurities including B, Ga, P, O and processing parameters such as oxidation temperature. To suppress the degradation, reducing the concentration of B and O or substituting boron by gallium as dopant was found to be effective. These findings are in agreement with a model attributing the lifetime degradation to oxygen and boron. Copyright © 2000 John Wiley & Sons, Ltd.

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Lifetime stability of gallium‐doped multicrystalline silicon wafers has been evaluated under illumination. Quality and stability of the Ga‐doped multicrystalline silicon wafers were intensively studied by means of quasi‐steady‐state photocondcutance lifetime measurement. Results show that as‐grown Ga‐doped multicrystalline silicon wafers have high lifetimes, and no significant degradation was observed under illumination. The Ga‐doped multicrystalline silicon wafers are a promising material for future photovoltaics. Copyright © 2003 John Wiley & Sons, Ltd.

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