摘要： Cesium based inorganic perovskite CsPbI3 solar cells have attracted arising research interests due to its improved thermal stability and reduced ion immigration in comparison with their organic-inorganic counterparts. However, the preferred black perovskite CsPbI3 is thermodynamically unstable at room temperature, and it will spontaneously transform to the undesired non-photoactive yellow phase. The essence of the phase instability is the small size of Cs cation, which is not suitable to support the three-dimensional PbI3- framework. The large lattice strain induced from the ion size mismatch will drive the CsPbI3 lattice structure from three dimensional (3D) perovskite phases to one dimensional (1D) non-perovskite phase. Therefore, the improvement of the lattice symmetry and reduction of the lattice strain are the two directions to dissolve the problem of phase instability. The nanocrystal-induced phase stabilization is one strategy to reduce the lattice strain by increasing the surface area of the crystals in the film, which is normally realized by introducing organic long-chain alkyl amine in the precursor solution. The shortcoming of this method is its negative effect of a large number of grain boundaries on the carrier transport and injection. Currently, the most widely used and effective strategies are the DMAI related methods, including the DMAI additive methods and the HI derived methods. The HI derived methods, normally named HI additive, HI?PbI2 or HPbI3 precursor, are demonstrated inevitably bring the DMA byproduct in the precursor solution from the reaction between HI and DMF. Although there are already several works focused on the elaboration of the final perovskite layer with the pure inorganic phase or still the organic-inorganic composite, the conclusion is still a huge controversy. Therefore, whether the organic DMA cation exists, how much the organic DMA cation in the crystal lattice, the properties of the DMA/Cs mixed perovskite phase and the mechanism of the DMAI-assisted formation of the Cs base perovskite thin film are still unclear. In this work, we tracked the chemical composition, phase and bandgap of the perovskite layer during the thermal treatment. It was found that, with a controlled thermal annealing process, a more thermodynamically stable perovskite of mixed cation DMA0.15Cs0.85PbI3 could form with a certain amount of Cs4PbI6 residue. Unlike other mixed cation perovskite materials, the composition of DMA/Cs mixed perovskite is well fixed instead of a continuous component distribution. Further thermal annealing transformed the film into C(cid:26)(cid:4)(cid:14)(cid:18)/(cid:25)3 and then into D(cid:26)(cid:4)(cid:14)(cid:18)/(cid:25)3. The DMA0.15Cs0.85PbI3 phase exhibits a more symmetrical structure, a narrower bandgap, and superior phase stability than that of C(cid:26)(cid:4)(cid:14)(cid:18)/(cid:25)3. These findings will benefit the in-depth understanding of the properties of inorganic perovskite and their phase stability issue.