Investigation On The Application Of Organic Ammonium Salt Based Two-dimensional Perovskite Materials In Flexible Perovskite Solar Cells

The light-weight and flexibility of organic-inorganic perovskite materials provided the prerequisites of researches on flexible perovskite solar cells（f-PSCs）.To data,the power conversion efficiency（PCE）of f-PSCs has exceeded 23%.However,the three-dimensional（3D）perovskite films in flexible devices still suffered from poor mechanical properties,internal defect density and insufficient internal carrier separation efficiency,which seriously limited the development of f-PSCs.To solve the above problems,perovskite thin films with both mechanical strength and excellent photovoltaic properties were obtained by introducing two-dimensional（2D）perovskite into 3D perovskite thin films,the main research contents and results were as followed:（1）Ruddlesden-Popper type 2D perovskite（4-Py A）₂Pb I₄ was synthesized based on the organic ammonium salt 4-pyridinylmethylammonium Iodide（4-Py AI）and used as seeds layer to optimize the crystallization process of perovskite layers.The 2D perovskite,which entered the grain boundary of 3D perovskite after annealing and acted as a"tape",reduced the total tensile stress of perovskite layer by reducing the stiffness of the perovskite layer and releasing the internal residual stresses.The characterization showed that the flexibility of the 2D/3D perovskite layer was improved.On the other hand,the highly-oriented 2D perovskite（4-Py A）₂Pb I₄ as seeds significantly enhanced the（100）lattice plane of 2D/3D perovskite,reducing the internal defects of the perovskite layer.As a result,high efficiencies of 21.97%were obtained for the f-PSCs,and the f-PSCs maintained 90%of the initial PCE after 2500 times bending.（2）The problem of insufficient excitons separation ability in flexible devices could be solved by doping ferroelectric materials in the perovskite layer.The 2D perovskite（3-Py A）₂Pb I₄ with ferroelectricity was successfully synthesized by changing the position of the methylammonium cation attached to the pyridine ring.We added 2D perovskite directly into the 3D perovskite precursor solution to accomplish the doping of 3D perovskite.The introduction of ferroelectric 2D perovskite enhanced the built-in electric field,improved the efficiency of exciton separation,and suppressed the nonradiative complexation in the device.According to the characterization of the perovskite films,the 2D perovskite optimized the 3D perovskite crystallization process,forming perovskite films with more uniform grain distribution.As a result,an impressive PCE over 23%has been achieved by the f-PSCs with outstanding ambient stability.Moreover,the piezoelectric 2D perovskite intrigued a decreased hole transport barriers under tensile stress.