Two-dimensional　(2D)　RuddLesden-Popper　hybrid　perovskites　(RPHPs)　have　shown　enormous　potentiaL　for　photoelectric　applications　owing　to　their　advantages　of　structural　diversity　and　unique　physical　properties.　Despite　extensive　studies,　the　cage-incorporation　of　secondary　amines　(e.g.,　dimethylamine,　DMA)　to　explore　2D　RPHP5　remains　a　great　challenge.　Herein,　we　present　a　new　member　of　2D　RPHP5,　(BA)(2)　(DMA)Pb2Br7　(1,　BA(+)　=　n-butyLammonium),　for　which　organic　DMA(+)　cations　are　enclosed　in　perovskite　cavities.　The　inorganic　perovskite　sheets　and　organic　BA(+)　spacing　Layers　are　arranged　in　the　alternate　packings,　resembling　a　2D　quantum-well　motif.　This　feature　is　advantageous　for　the　photoconductivity　properties.　Consequently,　the　crystal-based　array　detectors　of　1　exhibit　strong　photodetection　performances,　including　high　detectivity　(2.0　x　10(11)　Jones),　Large　responsivity　(31.1　mA　W-1),　and　fast　response　time　(similar　to　8　mu　s).　Moreover,　its　intrinsic　2D　quantum-well　structure　endows　significant　anisotropy　of　conductivity　and　optical　absorption,　which　account　for　the　strong　polarization　response　with　a　Large　dichroic　ratio　of　similar　to　1.43,　falling　in　the　range　of　other　2D　RPHP5.　These　results　reveal　the　potentiaL　of　1　for　photodetection　and　simultaneously　shed　Light　on　the　research　on　new　candidates　of　2D　RPHP5.