Nb-Doping TiO₂ Electron Transporting Layer for Efficient Perovskite Solar Cells

For improvement of the electron transporting and charge separation in the interface of TiO2 and perovskite, the smooth and compact Nb-doping TiO2 electron transporting layer was successfully prepared by a hydrolysis–pyrolysis method using an acidic titanium isopropoxide solution in isopropanol and niobium chloride (NbCl5) as the niobium source. The planar perovskite solar cells with the undoped TiO2 electron transporting layer gave a photoelectric conversion efficiency (PCE) of 14.56%, while the planar perovskite solar cells with the 2.5% Nb-doping TiO2 electron transporting layer obtained a PCE of 15.97%. When the TiO2 nanorod array was introduced between the 2.5% Nb-doping TiO2 electron transporting layer and the perovskite thin film, the corresponding perovskite solar cells achieved a PCE of 18.88% under illumination of simulated AM 1.5 sunlight (100 mA cm–2).