Tuning the structural and electronic properties of halide perovskite material is an effective method to promote its device performance. Increasing the grain size can decrease grain boundaries and further reduce defects. Regulating the band structure will improve the separation and extraction efficiency of carriers. In this work, high-quality CsPbBr films with increased crystallinity, better preferential orientation and improved carrier dynamics are achieved, using partial wetting transparent monolayer graphene as an interlayer. It is demonstrated that graphene can partially shield the surface potential field of the substrates, resulting in a changed preferred orientation of the CsPbBr. The reduced interaction between the substrates and the perovskite effectively decreases the diffusion barrier of adatoms, increasing the grain size and crystallinity. Besides, the presence of graphene also tunes the band structure of the perovskite with increased p-type doping, which changes the band offset at perovskite substrate interface. An improved charge extraction can be achieved on perovskite/G/ITO interface due to increased band offset while a reduced charge extraction is observed on perovskite/G/Au interface. As a result, the corresponding photodetector with graphene demonstrates better performance than that without graphene. Our study will provide more ideas for tuning the perovskite structure and energy bands to achieve better device performance.