A multi-dimensional conductive heterojunction structure, composited by TiO₂, SnO₂, and Ti₃C₂T_X MXene, is facilely designed and applied as electron transport layer in efficient and stable planar perovskite solar cells. Based on an oxygen vacancy scramble effect, the zero-dimensional anatase TiO₂ quantum dots, surrounding on two-dimensional conductive Ti₃C₂T_X sheets, are in situ rooted on three-dimensional SnO₂ nanoparticles, constructing nanoscale TiO₂/SnO₂ heterojunctions. The fabrication is implemented in a controlled low-temperature anneal method in air and then in N₂ atmospheres. With the optimal MXene content, the optical property, the crystallinity of perovskite layer, and internal interfaces are all facilitated, contributing more amount of carrier with effective and rapid transferring in device. The champion power conversion efficiency of resultant perovskite solar cells achieves 19.14%, yet that of counterpart is just 16.83%. In addition, it can also maintain almost 85% of its initial performance for more than 45 days in 30–40% humidity air; comparatively, the counterpart declines to just below 75% of its initial performance.