Hydrogen and nitrogen codoping of anatase TiO for efficiency enhancement in organic solar cells.

TiO has high chemical stability, strong catalytic activity and is an electron transport material in organic solar cells. However, the presence of trap states near the band edges of TiO arising from defects at grain boundaries significantly affects the efficiency of organic solar cells. To become an efficient electron transport material for organic photovoltaics and related devices, such as perovskite solar cells and photocatalytic devices, it is important to tailor its band edges via doping. Nitrogen p-type doping has attracted considerable attention in enhancing the photocatalytic efficiency of TiO under visible light irradiation while hydrogen n-type doping increases its electron conductivity. DFT calculations in TiO provide evidence that nitrogen and hydrogen can be incorporated in interstitial sites and possibly form NH, NH and NH defects. The experimental results indicate that NH defects are most likely formed and these defects do not introduce deep level states. Furthermore, we show that the efficiency of P3HT:ICBA-based organic photovoltaic devices is enhanced when using hydrogen-doping and nitrogen/hydrogen codoping of TiO, both boosting the material n-type conductivity, with maximum power conversion efficiency reaching values of 6.51% and 6.58%, respectively, which are much higher than those of the cells with the as-deposited (4.87%) and nitrogen-doped TiO (4.46%).