The Study Of Electronic Structures And Chemical Reactions At Metal/perovskite Interfaces

Perovskite solar cells(PSCs)have attracted considerable interests and attention,due to the advantages of high power conversion efficiency,low cost and flexible preparation.Therefore,PSCs have become a research focus in the field of solar cells.Currently,the maximum power conversion efficiency of PSCs has reached 23%,already comparable to some inorganic solar cells.But stability issues of PSCs are still unsolved,which limit its commercial applications.In PSCs,metal electrodes are the important component,and commonly used to collect charge carriers from the active layer.However,it is found that ion migration and chemical reactions occur at metal/perovskite interfaces,which affect the stability of devices significantly.Therefore,a thorough investigation of metal/perovskite interfaces properties is helpful for understanding the degradation mechanism of device performance,which could provide an abundant theoretical guidance for high-stability PSCs fabrication.Based on the above research background,by using surface-sensitive photoemission spectroscopy,we investigate the metal/perovskite interface properties,including interface electronic structures and interface chemical reactions.The results of this dissertation are as follows:(1)The chemical reactions and ion migration at Ag/CH3NH3PbI3 interfaces are investigated by in-situ X-ray photoelectron spectroscopy(XPS)and synchrotron radiation photoemission spectroscopy(SRPES).It is found that during the deposition of Ag onto CH3NH3PbI3 surface,Ag atoms could react with CH3NH3PbI3 layers,leading to the decomposition of CH3NH3PbI3 as well as the formation of PbI2,AgI and metallic Pb species.Upon Ag deposition,the intensities of C 1s and N 1s spectra gradually decrease,but the intensity of I 3d increases anomalously,which provides direct experimental evidences for the migration of iodide ions from CH3NH3PbI3 subsurface to Ag electrode.Moreover,the energy level alignment at Ag/CH3NH3PbI3 interfaces is investigated by ultraviolet photoelectron spectroscopy(UPS).It is foung that the contact of Ag electrode and perovskite layers induces a downward interfacial dipole at Ag/CH3NH3PbI3 interfaces,which may further facilitate iodide ion migration from perovskite layers to Ag electrode,resulting in the decomposition of perovskite layers and the corrosion of Ag electrode.(2)The chemical reactions and ion migration at Al/CH3NH3PbI3 interfaces are investigated by in-situ XPS and SRPES.It is found that during the deposition of Al onto CH3NH3PbI3 surface,A1 atoms could react with CH3NH3PbI3 layers strongly,leading to the decomposition of CH3NH3PbI3 as well as the formation of AlI3,C-N-Al complex and metallic Pb species.In order to obtain surface sensitive information,we scan the N 1 s spectra by changing the detection angles.It is shown that the N 1 s signal collected at grazing emission is much stronger than that at the normal emission,suggesting that the reaction intensity decreases as the depth increases.Upon Al deposition,the intensities of C 1s and Pb 4f spectra gradually decrease,but the intensity of I 3d increases anomalously,which provides direct experimental evidences for the migration of iodide ions from CH3NH3PbI3 subsurface to A1 electrode.Moreover,the energy level alignment at Al/CH3NH3PbI3 interfaces is investigated by UPS.It is foung that the contact of A1 electrode and perovskite layers induces the downward band bending and interfacial dipole at Al/CH3NH3PbI3 interfaces,which may further facilitate iodide ion migration from perovskite layers to Al electrode,resulting in the decomposition of perovskite layers and the corrosion of Al electrode.(3)The chemical reactions and ion migration at Ca/CH3NH3PbI3 interfaces are investigated by in-situ XPS and SRPES.It is found that during the deposition of Ca onto CH3NH3PbI3 surface,Ca atoms could react with CH3NH3PbI3 layers strongly,leading to the decomposition of CH3NH3PbI3 as well as the formation of CaI2 and metallic Pb species.Upon Ca deposition,the intensities of C Is,N 1s and Pb 4f spectra gradually decrease,but the intensity of I 3d increases anomalously,which provides direct experimental evidences for the migration of iodide ions from CH3NH3PbI3 subsurface to Ca electrode.Moreover,the energy level alignment at Ca/CH3NH3PbI3 interfaces is investigated by UPS.It is foung that the contact of Ca electrode and perovskite layers induces the downward band bending and interfacial dipole at Ca/CH3NH3Pbl3 interfaces,which may further facilitate iodide ion migration from perovskite layers to Ca electrode,resulting in the decomposition of perovskite layers and the corrosion of Ca electrode.