Normal (n-i-p) perovskite solar cells (PSCs) have received increasing attention due to their advantages such as high conversion efficiency and good stability. Tin dioxide is an ideal electron transport layer material for normal perovskite solar cells. Among various available electron transport layers, tin dioxide stands out because of its excellent stability, low density of defect states, and appropriate energy levels. The interface defects between tin dioxide and perovskite are the key factors restricting the improvement of the conversion efficiency in perovskite solar cells. Therefore, a method of fabricating normal perovskite solar cells based on the buried interface modification strategy is proposed in this work. By doping methylammonium bromide into tin dioxide to form a buried interface, the interface defects between tin dioxide and perovskite are reduced, the electron mobility of tin dioxide is enhanced, and the growth of high-quality perovskite materials is promoted. The conversion efficiency of the normal perovskite solar cells reaches 23.12%, providing an effective strategy for fabricating high-efficiency normal perovskite solar cells.