초록
Many research groups have studied tandem or multi-junction cells to overcome this low efficiency and degradation. In multi-junction cells, band-gap engineering of each absorb layer is needed to absorb the light at various wavelengths efficiently. Various absorption layers can be formed using multi-junctions, such as hydrogenated amorphous silicon carbide (a-SiC:H), amorphous silicon germanium (a-SiGe:H) and microcrystalline silicon (${\mu}c$-Si:H), etc. Among them, ${\mu}c$-Si:H is the bottom absorber material because it has a low band-gap and does not exhibit light-induced degradation like amorphous silicon. Nevertheless, ${\mu}c$-Si:H requires a much thicker material (>2 mm) to absorb sufficient light due to its smaller light absorption coefficient, highlighting the need for a high growth rate for productivity. ${\mu}c$-SiGe:H has a much higher absorption coefficient than ${\mu}c$-Si:H at the low energy wavelength, meaning that the thickness of the absorption layer can be decreased to less than half that of ${\mu}c$-Si:H. ${\mu}c$-SiGe:H films were prepared using 40 MHz very high frequency PECVD method at 1 Torr. SiH4 and GeH4 were used as a reactive gas and H2 was used as a dilution gas. In this study, the ${\mu}c$-SiGe:H layer for triple solar cells applications was performed to optimize the film properties.