Effect of TiO 2 Antireflection Layer with Various Conductivities and Refractive Indices on Performance of Amorphous Silicon/Amorphous Silicon Germanium Tandem Solar Cells

TiO 2 films were prepared by RF magnetron sputtering with process variations of substrate temperature and oxygen dilution ratio to investigate the effect of the optoelectronic properties of TiO 2 films on antireflection characteristics in solar cells. With an increase in substrate temperature from RT to 350 °C, the conductivity and refractive index of TiO 2 films increased. However, the absorption coefficient also increased. In the case of oxygen-diluted sputtering (0.5–1%), the conductivity and refractive index decreased with the increase in oxygen dilution. On the other hand, the absorption coefficient decreased simultaneously. To evaluate these optoelectronic property variations of TiO 2 films in terms of the antireflection effect in solar cells, amorphous silicon (a-Si:H)/amorphous silicon germanium (a-SiGe:H) tandem solar cells with various optoelectronic properties and thicknesses (20–40 nm) of TiO 2 films were fabricated. The TiO 2 film deposited at 350 °C and 0.5% oxygen dilution showed a high conductivity (∼10 -3 Ω -1 cm -1 ) and refractive index (∼2.56 at 550 nm). The fabricated tandem cell with the TiO 2 antireflection layer showed an efficiency of 11.22%, whereas the reference cell without TiO 2 exhibited an efficiency of 10.97%.