Enhancing　the　lifetime　of　perovskite　solar　cells　(PSCs)　is　one　of　the　essential　challenges　for　their　industrialization.　Although　the　external　encapsulation　protects　the　perovskite　device　from　the　erosion　of　moisture　and　oxygen　under　various　harsh　conditions.　However,　the　perovskite　devices　still　undergo　static　and　dynamic　thermal　stress　during　thermal　and　thermal　cycling　aging,　respectively,　resulting　in　irreversible　damage　to　the　morphology,　component,　and　phase　of　stacked　materials.　Herein,　the　viscoelastic　polymer　polyvinyl　butyral　(PVB)　material　is　designed　onto　the　surface　of　perovskite　films　to　form　flexible　interface　encapsulation.　After　PVB　interface　encapsulation,　the　surface　modulus　of　perovskite　films　decreases　by　nearly　50%,　and　the　interface　stress　range　under　the　dynamic　temperature　field　(-40　to　85　degrees　C)　drops　from　-42.5　to　64.8　MPa　to　-14.8　to　5.0　MPa.　Besides,　PVB　forms　chemical　interactions　with　FA+　cations　and　Pb2+,　and　the　macroscopic　residual　stress　is　regulated　and　defects　are　reduced　of　the　PVB　encapsulated　perovskite　film.　As　a　result,　the　optimized　device＇s　efficiency　increases　from　22.21%　to　23.11%.　Additionally,　after　1500　h　of　thermal　treatment　(85　degrees　C),　1000　h　of　damp　heat　test　(85　degrees　C　&　85%　RH),　and　250　cycles　of　thermal　cycling　test　(-40　to　85　degrees　C),　the　devices　maintain　92.6%,　85.8%,　and　96.1%　of　their　initial　efficiencies,　respectively.　Viscoelastic　PVB　material　is　innovatively　designed　to　form　a　flexible　interface　encapsulation.　The　Surface　modulus　and　interface　stress　concentration　zone　are　effectively　alleviated.　The　stability　breakthroughs　in　IEC　61215　(thermal　treatment　at　85　degrees　C,　damp　heat　test　(85　degrees　C　&　85%　RH),　thermal　cycling　test　(-40　to　85　degrees　C))　has　achieved　through　the　systemic　encapsulation　by　combining　internal　and　external　encapsulation.　image