Structural and interfacial properties of large area n-a-Si:H/i-a-Si:H/p-c-Si heterojunction solar cells

Large area (72 cm2) doping inversed HIT solar cells (n-a-Si:H/i-a-Si:H/p-c-Si) were investigated by High Resolution Transmission Electron Microscopy (HR-TEM), Spectroscopic Ellipsometry (SE), Fourier Transform Infrared Attenuated Total Reflection spectroscopy (FTIR-ATR) and current-voltage (I-V) measurement. Mixture of microcrystalline and amorphous phase was identified via HR-TEM picture at the interface of i-a-Si:H/p-c-Si heterojunction. Using multilayer and Effective Medium Approximation (EMA) to the SE data, excellent fit was obtained, describing the evolution of microstructure of a-Si:H deposited at 225 °C on p-c-Si. Cody energy gap with combination of FTIR-ATR analyses were consistent with HRTEM and SE results in terms of mixture of microcrystalline and amorphous phase. Presence of such hetero-interface resulted poor open circuit voltage, Voc, of the fabricated solar cell devices, determined by I-V measurement under 1 sun. Moreover, Voc was also estimated from dark I-V analysis, revealing consistent Voc values. Efficiencies of fabricated cells over complete c-Si wafer (72 cm2) were calculated as 4.7 and 9.2 %. Improvement in efficiency was interpreted due to the back surface cleaning and selecting aluminum/silver alloy as front contact.

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