Perovskite compounds have attracted much attention because of their photovoltaic properties. As research of perovskite soar cells (PSCs) has progressed over the last eight years, necessity of stability improvement has emerged due to low stability of three-dimensional (3D) perovskite compounds, which are widely applied as the light absorber of PSCs. Recently, quasi two-dimensional (2D) perovskite compounds, whose general formula is (RNH3)2Bn-1PbX3n+1, is regarded as one of the promising PSCs materials to solve this problem. Actually some groups reported applications of quasi 2D perovskites to photovoltaic devices with enhanced stability. It is notable that only methylamine cation (MA) has been used as the B site cation in such devices. To the best of our knowledge, there have been no reports of quasi 2D perovskite compounds in which the B site cation is formamidine cation (FA) or Cs+, although FAMX3 and CsMX3 are common compounds in this field. Here, we report properties and appliations of these compounds. Quasi 2D perovskite compounds, which consist of hexlyamine (HA) iodide, lead iodide, and MAI, FAI, and CsI as a B site cation, were fabricated by spin-coat method as films. These films were investigated by 2D XRD measurements to confirm the quasi 2D perovskite structures. A diffraction peak at 3.8° originated from the d-spacing value of 23 Å was only observed in HA2FAPb2I7 (HAFAPbI). This value is equal to the interlayer distance of quasi 2D perovskite structure. This indicates the formation of quasi 2D perovskite layered structure at the film surface and crystalline growth partly perpendicular to the film. This perpendicular crystalline growth is well-suited to photovoltaic applications, because it allows charges to migrate within the perovskite layers without disturbance. Each sample was applied to mesoscopic cells. Photovoltaic properties of HAFAPbI was superior to other homologous samples because of unique crystalline growth, which suit to charge transportation.

Introduction of formamidine and Cs cation to quasi two-dimensional perovskites

254th National Meeting (2017)

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