General Method To Define the Type of Carrier Transport Materials for Perovskite Solar Cells via Kelvin Probes Microscopy

Various kinds of semiconductor materials, organic and inorganic, served effectively as electrons or holes transport materials for perovskite solar cells (PSCs). However, their direct function has rarely been reported other than examining their effect in the final photovoltaic devices. In this work, a general and facile method was employed to determine to a point the type of carriers transferred by both SnO2 and NiO popular charge transport materials in PSCs via scanning Kelvin probes microscopy. The sign of the increment of the surface potential voltage measured tells directly whether electrons or holes were extracted by these carrier transport materials while its mapping can also provide the extraction difference between grain interiors and grain boundaries. Both MAPbI(3) and CsFAMA triple cation perovskites were involved in the test with the same conclusion. Along with time-resolved photoluminescence, the extraction rate of each kind of material can be distinguished. This work definitely offers us a general and effective method to distinguish the carrier transport ability of either electrons or holes transport materials with indisputable clarification of carrier types and further to screen out optimal carrier transport materials for perovskite solar cells and more.