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

For improvement of the electron transporting and charge separation in the interface of TiO 2 and perovskite, the smooth and compact Nb-doping TiO 2 electron transporting layer was successfully prepared by a hydrolysis–pyrolysis method using an acidic titanium isopropoxide solution in isopropanol and niobium chloride (NbCl 5 ) as the niobium source. The planar perovskite solar cells with the undoped TiO 2 electron transporting layer gave a photoelectric conversion efficiency (PCE) of 14.56%, while the planar perovskite solar cells with the 2.5% Nb-doping TiO 2 electron transporting layer obtained a PCE of 15.97%. When the TiO 2 nanorod array was introduced between the 2.5% Nb-doping TiO 2 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 ).