Inorganic cesium lead triiodide (CsPbI ₃) perovskite films show great prospect due to their high thermal stability and ideal band gap energy. To be used as a photovoltaic absorber, the CsPbI ₃must form the black phase (α-CsPbI ₃). To prepare high-quality CsPbI ₃films with phase stability in air at low temperatures, alkali metal iodides and hydroiodic acid (HI) additives are added into precursor solution. The results show that the quality and the phase stability of CsPbI ₃with alkali metal iodides and HI additives are obviously improved compared with those with only HI additive. The SEM images show that the CsPbI ₃film with 2.5% KI additive becomes more compact than that without KI additive and has no visible pinholes. As the KI additive increases, pinholes start to appear. From the XRD, it can be seen that the crystallinity of perovskite is improved when KI additive increases to 5.0%, while it starts to decrease with KI additive further increasing. The PL intensity of the CsPbI ₃film with 2.5% KI additive is higher than the others’, implying a relatively low non-radiative recombination loss and low defect state in that film. And the CsPbI ₃film with 2.5% KI additive exhibits increased absorption in the visible region, which is beneficial to enhancing the efficiency of perovskite solar cells. Considering the SEM images, crystallinity, PL intensity and light absorption of perovskite, the optimized KI additive is 2.5% in our work. For the CsPbI ₃film with NaI additive, the SEM images show that the films become more compact and have no visible pinholes when NaI additive is 5%. As the NaI additive increases, pinholes appear. The crystallinity of perovskite increases with NaI additive increasing. The PL intensity of the CsPbI ₃film with 5% NaI additive is higher than the others’, implying lower defect states in films. And the CsPbI ₃film with 5% NaI additive exhibits the improved absorption in the visible region. Considering the SEM images, crystallinity, PL intensity and light absorption of perovskite, the optimized NaI additive is 5%. Therefore, adding alkali metal iodides and HI is an effective method to further improve the stability and efficiency of CsPbI ₃perovskite solar cells.