Anti-reflection porous SiO2 thin film deposited using reactive high-power impulse magnetron sputtering at high working pressure for use in a-Si:H solar cells

Porous SiO2 thin films with low reflectance and high transmittance were obtained using reactive high power impulse magnetron sputtering (HIPIMS) at a high working pressure of 6.67 Pa (50 mTorr). The average transmittance (450-600 nm) of the SiO2 thin films was 94.45%. In comparison, SiO2 thin films deposited at a low working pressure of 0.27 Pa (2 mTorr) showed an average transmittance of 91.26%. The improvement in the transmittance was attributed to the lower refractive index resulting from the porous structure of the SiO2 thin films. To examine the effect of the anti-reflection SiO2 coating, an a-Si:H solar cell was produced on fluorine-doped tin oxide (FTO) glass. The initial energy conversion efficiency for cells using the anti-reflection, SiO2-coated FTO glass was 11.75%, higher than the 10.75% for the sample using the bare FTO glass. The increase in the short-circuit current density (Jsc) due to the decreased light reflectance was the largest contributor to the increase in the a-Si:H solar cell efficiency.