Wide-spectrum Mg and Ga co-doped ZnO TCO thin films for solar cells grown via magnetron sputtering with H2 introduction

Wide-spectrum Mg and Ga co-doped ZnO transparent conductive oxide (TCO) thin films are deposited via magnetron sputtering at various H2 flow rates on glass substrates. The structural, electrical, and optical properties of MGZO thin films are investigated with different H2 flow rates. The experiment results show that the MGZO thin films are polycrystalline with a hexagonal wurtzite structure exhibiting a preferred (0 0 2) crystal plane orientation. The carrier concentration remarkably increases from 5.15 × 1019 cm−3 to 2.12 × 1020 cm−3 with increasing the H2 flow rate from 0 sccm to 4.0 sccm and then decreases when further increasing the H2 flow rate. The glass/MGZO thin film deposited at the H2 flow rate of 4.0 sccm exhibits the lowest resistivity of 1.96 × 10−3 Ω cm (film thickness d ∼ 548 nm) and an average transmittance (Ta) of 80.5% in the wavelength range from 340 nm to 1100 nm. Optical measurements indicate that the optical band gap (Eg) of MGZO thin films varies from 3.45 eV to 3.78 eV with adjusting H2 flow rate from 0 sccm to 12.0 sccm. The obtained MGZO thin films with an appropriate thickness are preliminarily applied in p-i-n type hydrogenated amorphous silicon (a-Si:H) thin film solar cells. The a-Si:H solar cell with MGZO layer presents higher quantum efficiency in the short wavelength region than that with GZO layer, resulting from widened optical band gap.