Although　perovskite　films　have　excellent　extinction　coefficients,　further　increase　of　the　light-absorbing　capacity　by　increasing　the　thickness　of　the　active　layer　is　always　required　in　perovskite　solar　cells　(PSCs).　However,　to　maintain　the　morphology　quality　of　the　perovskite　layer,　the　film　thickness　is　subject　to　certain　restrictions.　To　increase　the　light　absorbance　without　significantly　inflating　the　perovskite　film　while　keeping　the　high　quality　of　the　perovskite　film,　herein,　we　added　an　aqueous　solution　of　gold　nanorods　(AuNRs)　to　the　perovskite　precursor　solution　via　a　so-called　asynchronous　synergistic　effect　(ASE)　strategy　of　water　and　AuNR.　The　former　improves　the　quality　of　the　perovskite　film　during　the　crystallization　process　to　reduce　defect　density　and　enhance　carrier　mobility.　Simultaneously,　the　latter　increases　the　light　absorption　of　the　perovskite　layer　through　the　localized　surface　plasmon　resonance　(LSPR)　effect　when　the　device　is　exposed　to　light.　We　show　that　the　ASE　strategy　leads　to　an　excellent　power　conversion　efficiency　(PCE)　of　21.73　%　and　outstanding　long-term　stability,　which　can　retain　95　%　of　its　initial　PCE　after　storage　for　three　months　in　an　air　atmosphere.