TiO2/CH3NH3PbI3-based photovoltaic devices were fabricated by a spin-coating method using a mixture solution of niobium(V) ethoxide, and the effects of niobium (Nb) addition to TiO2 layers were investigated. The lattice distance and energy gap of the TiO2 were almost same after Nb addition. The elemental mapping and sheet resistance measurements indicated a wide distribution of Nb and Ti, and a decrease in sheet resistance by Nb addition. The external quantum efficiency and internal quantum efficiency increased by Nb addition to compact TiO2 and mesoporous TiO2 layers, which resulted in an increase in the current density and conversion efficiency of the cell.