Mixed halide perovskite is essential to construct highly efficient tandem solar cells, whereas halide segregation is a main issue hindering their device efficiency for this kind of perovskite materials. Herein, we modify the solvents for the mixed halide precursor solution to suppress halide segregation during fabrication process. An alternative solvent, N-Methyl pyrrolidone (NMP), is used to replace commonly used solvent, dimethyl sulfoxide (DMSO). It is shown that the halide segregation and the resultant carrier recombination are notably suppressed. The improvements brought by NMP may correlate with its moderate Lewis base property, which modifies the crystallization process of the mixed halide perovskite film. Consequently, the device performance is greatly improved by using NMP. The device efficiency is increased from less than 10% for DMSO solvent to approach 14% for NMP solvent. This work provides a facile way to improve the device efficiency, which also highlights on the importance of the solvents on halide segregation.