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Chemical Composition Evolution and Electrical Performance Degradation of TOPCon Solar Cells Under UV Exposure
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DOI：10.1002/pip.70132.png)
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Abstract
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The evolution of the chemical composition and the degradation of the electrical performance of tunnel oxide passivated contact (TOPCon) solar cells under ultraviolet (UV) exposure are analyzed in this paper. Compared to the rear-side structure (SiOx/n+-poly-Si/Al2O3/SiNx) of TOPCon solar cells, the front-side structure (SiNx/Al2O3) exhibits an inferior resistance to UV with a dramatic rise of J0. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and depth profiling X-ray photoelectron spectroscopy (XPS) are used to characterize and to monitor the chemical composition of the front-side structure during UV60 exposure. The free hydrogen concentration in the passivation layers grows during UV illumination, and the breakage of N–H bonds in SiNx layer is found to be the second source of potential hydrogen loss besides the well-known Si–H bonds breaking. Meanwhile, Al–O bonds are also found to be dissociated by UV exposure, accompanying the transformation from Al2O3 to Al–OH and the valence states variation of silicon. The free oxygen diffuses into SiNx/Al2O3 interface and Al2O3/Si interface, with the concentration of oxygen increasing. The XPS spectra also demonstrate that numerous oxygen vacancies form in Al2O3 layer after UV60 illumination, indicating that the film quality is getting damaged. Hydrogen-related degradation and oxygen-related degradation have a joint effect on the deterioration of surface recombination, with the relative decline of 3.46% for Voc after UV60 exposure. In addition, the increase of the front contact resistivity contributes to the relative drop of 2.82% for fill factor. Eventually, a dramatic power conversion efficiency degradation of 6.72% is observed for TOPCon solar cells after UV60 illumination.
Keywords:
chemical composition evolution
electrical performance degradation
TOPCon solar cell
UV exposure
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