Optimizing charge transport and band-offset in silicon heterojunction solar cells: impact of TiO2 contact deposition temperature

Abstract Carrier selective contacts are a primary requirement for fabricating silicon heterojunction solar cells (SHSCs). TiO 2 is a prominent carrier selective contact in SHSCs owing to its excellent optoelectronic features such as suitable band offset, work function, and cost-effectiveness. Herein, we fabricated simple SHSCs in an Al/TiO 2 / p -Si/Ti/Au device configuration. Ultrathin 3 nm TiO 2 layers were deposited onto a p -type silicon substrate using the atomic layer deposition method. The deposition temperature of TiO 2 layers varied from 100 °C to 250 °C. X-ray photoelectron spectroscopic studies suggest that deposition temperature highly affects the chemical states of TiO 2 and reduces the formation of defective state densities at the Fermi energy. The optical band gap values of TiO 2 layers are also altered from 3.13 eV to 3.27 eV when the deposition temperature increases. The work function tuning from −5.13 eV to −4.83 eV has also been observed in TiO 2 layers, suggesting the variation in Fermi level tuning, which arises due to changes in carrier concentrations at higher temperatures. Several device parameters, such as ideality factor, trap density, reverse saturation current density, barrier height, etc, have been quantified to comprehend the effects of deposition temperature on photovoltaic device performance. The results suggest that the deposition temperature significantly influences the charge transport and device performance. At an optimum temperature, a significant reduction in charge carrier recombination and trap state density has been observed, which helps to improve power conversion efficiency.