Improvement of a-Si solar cell properties by using SnO2:F TCO films coated with an ultra-thin TiO2 layer prepared by APCVD

TiO₂-overcoated SnO₂:F transparent conductive oxide films were prepared by atmospheric pressure chemical vapor deposition (APCVD) and an effect of TiO₂ layer thickness on a-Si solar cell properties was investigated. The optical properties and the structure of the TiO₂ films were evaluated by spectroscopic ellipsometry and X-ray difractometry. a-Si thin film solar cells were fabricated on the SnO₂:F films over-coated with TiO₂ films of various thicknesses (1.0, 1.5 and 2.0 nm) and I–V characteristics of these cells were measured under 1 sun (100 mW/cm² AM-1.5) illumination. It was found that the TiO₂ film deposited by APCVD has a refractive index of 2.4 at 550 nm and anatase crystal structure. The conversion efficiency of the a-Si solar cell fabricated on the 2.0 nm TiO₂-overcoated SnO₂:F film increased by 3%, which is mainly attributed to an increase in open circuit voltage (V_oc) of 30 mV.