Research On Interface Engineering In Improving The Performance Of Perovskite Solar Cells

Organometallic hybrid perovskites have attracted much attention due to the many advantages,such as tunable band gap,high absorption coefficient,bipolar carrier migration,and long carrier life,especially in the field of photovoltaic applications.Within only 10 years,the photoelectric conversion efficiency(PCE)of perovskite solar cells(PSCs)has increased to 25.5%,which is expected to industrialization.Generally,PSCs mainly have two device structures:formal n-i-p structure and inverted p-i-n structure,which are composed of glass substrate,transparent conductive oxide,electron transport layer,perovskite photoelectric conversion layer,hole transport layer and back electrode.The photogenerated carriers of the perovskite layer pass through the grain boundaries and interfaces,and are transferred to the external circuit through the transport layer.However,at the grain boundary and all interfaces,the combination process is in competition with the extraction of photogenerated carriers,which limits the transport of carriers and restricts the photovoltaic performance and stability of PSCs.Therefore,interface engineering is an effective way to achieve better energy level matching,passivate perovskite traps,eliminate photocurrent hysteresis,delay charge recombination and improve the long-term stability of devices.This thesis expounds that improving the photovoltaic performance of PSCs by modifying different interfaces.The results are as followings:(1).Due to the bipolar carrier transport properties of perovskite materials,hole conductor-free PSCs based on carbon electrodes have attracted much attention due to their low cost,long-term stability,simple manufacturing technology and easy industrialization.In these devices,the carbon electrodes not only play as charge transfer channels,but also as hole extracting layers,thus the conductivity and hole mobility are critical for the performance.However,the hole mobility of carbon layers is relatively low.Here,low-temperature carbon layers were incorporated with Cu S nanostructures,in which the hole mobility was improved.After adding 1 wt.%Cu S,the PSCs yielded to the best power conversion efficiency of 11.28%,while the pure carbon electrode based PSCs attained the best power conversion efficiency of 9.36%which is slightly higher than that of the PSCs based on pure carbon counter electrode.This study demonstrates that it is an effective way to improve the hole transport property of carbon counter electrode by combining p-type Cu S with high hole mobility.(2).The inverted p-i-n PSCs have lower production cost,simple preparation process,low-temperature preparation,and weak hysteresis.The main reason for limiting its development is the hole transport layer of inverted PSCs.Ni Ox is a commonly used inorganic hole transport layer.Although it has high hole mobility,wide band gap,suitable valence band maximum(E_VBM),high conduction band minimum,easy synthesis and high stability.However,the hole carrier concentration in Ni Ox is low and the matching degree of the Fermi level and E_VBM still needs to be further improved.Therefore,in this chapter,we transfer the monolayer graphene(MLG)prepared by CVD to the surface of the Ni Ox layer.The energy level structure of the hole transport layer is more matched with MAPb I₃,and the interface between the hole transport layer and the perovskite layer is improved.And MLG serves as the base of MAPb I₃ crystals to improve the morphology of perovskite.Ultimately improve the photoelectric performance of the inverted PSCs.(3).Different organic cations will change the dimensions of perovskite materials.We synthesized one-dimensional(CH₃)₃SPb I₃ nanorods,two-dimensional(PEA)₂Pb I₄ nanosheets and three-dimensional Cs_0.1FA_0.9Pb I₃ thin films.One-dimensional(CH₃)₃SPb I₃ nanorods show ultra-high stability.And the photovoltaic performance is discussed by assembling solar cells.At the same time,we synthesized two-dimensional(PEA)₂Pb I₄ nanosheets and introduced them into the Cs_0.1FA_0.9Pb I₃film.The grain boundaries of Cs_0.1FA_0.9Pb I₃ and the interface between Cs_0.1FA_0.9Pb I₃ and the hole transport layer were effectively optimized,which can successfully prevent?-phase Cs_0.1FA_0.9Pb I₃from transforming into?-phase.Due to the embedded 2D(PEA)₂Pb I₄ nanosheets,a higher quality perovskite film is obtained,with longer carrier lifetime,lower density of trap states and higher stability.The resulting device can achieve 20.27%PCE and high stability.