CsPbBr₃ based perovskite solar cells have attracted an increasing attention owing to their high stability in ambient. The conduction band offset (CBO) between electron transportation layer and light absorb layer has important effects on the photovoltaic performance of perovskite solar cells. For the typical device configuration of FTO/TiO₂/CsPbBr₃/Carbon, the CBO value reaches to ~0.94 eV, which is too high to get efficient electron extraction. It is important to optimize the CBO so as to enhance the photovoltaic performance of the solar cells. In this work, we reduce the CBO value from 0.94 eV to 0.81 eV in the typical device configuration of FTO/TiO₂/CsPbBr₃/Carbon by using Sr²⁺ to modify the TiO₂ layer. The Sr-modified TiO₂ layer facilitates efficient extraction of electrons from CsPbBr₃ to electron transportation layer. Meanwhile, the Sr-modified TiO₂ layer suppresses the charge recombination rate in the perovskite solar cells. As a result, the power conversion efficiency of solar cells is enhanced from 5.92% to 7.22% by simply introducing a Sr-modified TiO₂ layer.