A Study Of The Electronic Structure At The CuPc/CsPbI₂Br Interface

While the environmental pollution and the depletion of fossil energy becomes more and more serious,humans are paying more and more attention to the development and utilization of various types of clean energy.The use of solar energy can be fully pollution-free with almost infinite reserves;therefore,the efficient use of solar energy becomes more and more important.While mankind has a long history of using solar energy,silicon solar cells nowadays have already been commercialized and entered people's daily lives.To convert solar energy into electricity more efficiently,reaches are also devoted to developing other solar cells,including dye-sensitized solar cells,copper indium gallium selenium solar cells,organic thin film solar cells,gallium arsenide germanium solar cells,and cadmium telluride solar cells.Due to the high light absorption coefficient,adjustable band gap,long carrier diffusion distance,and bipolar carrier transporting properties of organic–inorganic perovskites,the power conversion efficiency of perovskite solar cells in the past ten years has increased from 3.8%in 2009to current over 25%.Moreover,perovskite solar cells have the advantages of abundant raw materials,low costs,and simple manufacturing processes.Thus,they have widespread interests among photovoltaic community,making them a promising star in the photovoltaics.The interfacial electronic structures in the perovskite solar cells are vital in determining their performance.In contrast to the organic–inorganic perovskites,there has been few reports about the study of the interfacial structure of all-inorganic perovskites,even though they are more structurally stable.Herein,Cs Pb I₂Br perovskite thin films were firstly fabricated by one-step spin-coating on FTO.With the help of scanning electron microscope(SEM)and grazing incidence X-ray diffraction(GIXRD),the fabrication process has been optimized leading to the successful fabricated high quality Cs Pb I₂Br films.Then,in situ X-ray photoelectron spectroscopy(XPS)and ultraviolet photoelectron spectroscopy(UPS)measurements were carried out during the deposition of copper phthalocyanine(Cu Pc)to reveal the electronic structure at the Cs Pb I₂Br/Cu Pc interface.The present results show that no band bending was resolved at the Cs Pb I₂Br side whereas that there is?0.23 e V upward band bending as well as a dipole of?0.08 e V identified at the molecular side.The hole injection barrier as indicated by the energy Cs Pb I₂Br valance band maximum(VBM)to Cu Pc highest occupied molecular orbital(HOMO)was estimated to be?0.26 e V favoring hole extraction from Cs Pb I₂Br to Cu Pc.However,the electron blocking barrier of?0.04 e V as indicated by the offset between Cs Pb I₂Br conduction band minimum(CBM)and Cu Pc lowest unoccupied molecular orbital(LUMO)is too small to efficiently block electron transfer.Therefore,the present experimental study implies that Cu Pc may not be a promising hole transport material for high-performance solar cells using Cs Pb I₂Br as active layer.