Experimental and theoretical study of the synthesis of N-doped TiO2 by N ion implantation of TiO2 thin films

Highlights: • Reactive magnetron sputtering combined with ion implantation for crystalline TiO₂:N. • TRIDYN code for explaining the structural modifications induced by ion implantation. • Low Doses are required to avoid significant structural damages. • Ion penetration depth tuned by the accelerating voltage and the irradiation angle. Since major limitations of the Dye-Sensitized Solar Cells (DSSCs) efficiency are assumed to come from (i) the low resistivity of the generally used TiO₂ (ρ = 1 Ω·cm) and (ii) the undesired electron-hole recombination at the semiconductor/dye-electrolyte interfaces, the development of N-doped TiO₂ semiconductor (TiO₂:N) has attracted considerable interest. However, the synthesis of this material still remains a challenge as it is difficult to monitor (i) the doping level and (ii) the position of the nitrogen atoms into the titanium oxide lattice. In this context, the combination of Reactive Magnetron Sputtering (RMS) and Ion implantation (II) recently allowed to finely control the nitrogen chemistry of N-doped TiO₂ materials. However, the structural properties, such as the crystalline constitution and morphology of the implanted materials are of crucial interest for the intended application. Therefore, we performed a parametric study of the ion beam parameters on the physical and chemical properties of TiO₂:N in the aim of charge transport application in DSSCs and the results were supplemented by a simulation tool (i.e. TRIDYN software), allowing to distinguish this work from the others. Briefly, we observed that the sputtering of the ion implanted layer prevails with low accelerating voltages while the ion implantation process and its intrinsic effects are observed for high accelerating voltage conditions. We also demonstrated that the sputtering effect issue can be quite easily avoided for low dose conditions.