Inorganic　perovskites　with　cesium　(Cs+)　as　the　cation　have　great　potential　as　photovoltaic　materials　if　their　phase　purity　and　stability　can　be　addressed.　Herein,　a　series　of　inorganic　perovskites　is　studied,　and　it　is　found　that　the　power　conversion　efficiency　of　solar　cells　with　compositions　CsPbI1.8Br1.2,　CsPbI2.0Br1.0,　and　CsPbI2.2Br0.8　exhibits　a　high　dependence　on　the　initial　annealing　step　that　is　found　to　significantly　affect　the　crystallization　and　texture　behavior　of　the　final　perovskite　film.　At　its　optimized　annealing　temperature,　CsPbI1.8Br1.2　exhibits　a　pure　orthorhombic　phase　and　only　one　crystal　orientation　of　the　(110)　plane.　Consequently,　this　allows　for　the　best　efficiency　of　up　to　14.6%　and　the　longest　operational　lifetime,　TS80,　of　≈300　h,　averaged　of　over　six　solar　cells,　during　the　maximum　power　point　tracking　measurement　under　continuous　light　illumination　and　nitrogen　atmosphere.　This　work　provides　essential　progress　on　the　enhancement　of　photovoltaic　performance　and　stability　of　CsPbI3　−　xBrx　perovskite　solar　cells.　©　2020　The　Authors.　Published　by　WILEY-VCH　Verlag　GmbH　&　Co.　KGaA,　Weinheim