To explore the lead-free key scientific issue in perovskite,double perovskite based on AgBi and CuBi was naturally selected as a competitive candidate due to its fascinating functional features,such as self-powered circularly polarized light detection,X-ray detection,photoluminescence and so on.How-ever,the most challenging point is to simulate the structure and function of traditional lead-based perovskite in new double perovskite.At the same time,there are few suitable double perovskite sys-tems with optical and electrical potential.The above two points greatly limit the competitiveness of double perovskite.In order to solve this problem,firstly,by analyzing and comparing previous studies,we used 2,2-dimethylpropan-1-aminium(abbreviated as 2,2-DPA)as the organic template to assemble materials.Solid-to-solid phase transition materials(2,2-DPA)3Bi2I9 1 and(2,2-DPA)3Pb2I7 2 were con-structed.Along the path of lead-free and two-dimensional maintenance,we successfully synthesized(2,2-DPA)4AgBiI8 H2O 3 and(2,2-DPA)4CuBiI8 H2O 4.As two typical semiconductors,3 and 4 with narrower optical band gaps of 1.98 and 1.76 eV show obvious photo-response when the xenon lamp with intensity of 20 mW/cm2 is on or off,implying that they may be applied to light-harvesting and light-detecting de-vices.By referring to the phase transition mechanism of 1 and 2,3 may be caused by ordered-disordered transition of the organic part,which was proven to be the first solid-to-solid phase transition material with<100>-oriented layered double perovskites with n=1 by systematic characterization methods af-ter dehydration for all we know.We believed that this work can provide meaningful guidance for the development of lead-free double perovskites.