Methylammonium lead triiodide (CH3NH3PbI3) is an essential material in prototype perovskite solar cells, and its intrinsic electronic structures have been of great interest. In this study, the clean surface of single crystal samples of CH3NH3PbI3 was elucidated by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), and photoelectron yield spectroscopy (PYS), and was closely compared with as-prepared single crystal surfaces with considerable native impurities. Low-energy UPS and PYS successfully revealed a presence of electronic states exceeding the Fermi level, which are presumably attributed to electrons transferring from the surface impurities into the conduction band of CH3NH3PbI3.
Methylammonium lead triiodide (CH3NH3PbI3) is a fundamental material used for prototypical perovskite solar cells. The electronic properties of the interface between CH3NH3PbI3 and hole transporting materials play a crucial role in the efficient performance of these solar cells. However, the intrinsic characteristics of the interfaces where these materials directly come into contact with each other have not yet been defined since previous studies were performed using polycrystalline thin films of CH3NH3PbI3, which were confirmed to contain a considerable amount of impurities. In this study, x-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy were conducted to determine the interfacial electronic structure between CH3NH3PbI3 and 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) on the clean interface formed on the impurity-free single crystal surface of CH3NH3PbI3. Spontaneous hole injection from CH3NH3PbI3 to spiro-OMeTAD occurred at the direct contact sites between these materials, a phenomenon that was confirmed to be hindered by the presence of impurities at the interface.
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