Evaluating the Correlation Between Temperature Induced Hydrogen Loss and Surface Recombination Velocity in Passivation Degradation of c-Si/i.a-Si:H Solar Cells

• Noah Jones, Material Science, University of Delaware

• Ujjwal Das, Institute of Energy Conversion & Department of Materials Science & Engineering, University of Delaware
• Margaret Zeile, Institute of Energy Conversion & Department of Chemistry and Biochemistry, University of Delaware
• Tasnim Mouri, Institute of Energy Conversion & Department of Materials Science & Engineering, University of Delaware

Crystalline silicon (c-Si) solar cells are the predominant type of photovoltaic cells used in commercial applications. Despite their widespread use, c-Si cells exhibit significant surface defects causing surface recombination. To mitigate this issue, intrinsic amorphous silicon (i.a-Si:H) layers are deposited onto c-Si wafers to passivate the c-Si/i.a-Si:H interface. This study investigates the passivation of c-Si with i.a-Si:H, focusing on the effect of temperature-induced hydrogen loss on surface recombination at the c-Si/i.a-Si:H interface. Four c-Si/i.a-Si:H samples were prepared, with two samples having a 10 nm i.a-Si:H layer and the other two a 50 nm i.a-Si:H layer. Characterization techniques employed include Fourier Transform Infrared (FTIR) spectroscopy and Quasi-Steady-State Photoconductance (QSSPC) to understand the relationship between hydrogen loss and increase of surface recombination velocity. The passivation remained stable up to temperatures ≈ 250°C for the 10 nm layer samples and ≈350°C for the 50 nm layer samples. The activation energy for hydrogen loss was approximately 0.3 eV for the 10 nm layer (150 to 425°C) and 0.6 eV for the 50 nm layer (150 to 425°C), with the thinner layer exhibiting a lower activation energy due to its reduced thickness. Surface recombination velocity showed activation energies of around 1.5 eV for the 10 nm layer and 3.0 eV for the 50 nm layer, indicating a factor of five difference in activation energy between hydrogen loss and surface recombination. These findings suggest that while hydrogen loss initiates passivation degradation, other factors, such as oxygen’s impact on the i.a-Si:H structure or other impurities, may play a significant role in higher rate of passivation loss than hydrogen loss.