Research On The Modification Of Cathode Interface Materials In Non-fullerene Organic Solar Cells

In recent years,organic solar cells have attracted extensive attention due to their advantages such as lightweight,good mechanical flexibility and easy large-area printing.Cathode interface is an important part of organic solar cells,and significantly affects the efficiencies of organic solar cells.Water-soluble and alcohol-soluble organic materials are commonly used as cathode interface materials,but some of the groups in these materials,such as amine groups（-NH₂）,have strong chemical reactivity.Those can chemically react with high efficiency non-fullerene acceptors and conducting polymer poly（3,4-ethylenedioxythiophene）:poly（styrene sulfonate）（PEDOT:PSS）.In this thesis,the metal chelation strategy was adopted to inhibit the reactivity of the amine groups,and main results are summarized as follows:（1）Poly（allylamine）（PAA）contains amine groups in the side chain,which can form interfacial dipoles and reduce the work function of the electrode.The amine groups in PAA have strong reducibility,which is easy to react with IT-4F and destroy the chemical structure of non-fullerene acceptors.In this thesis,zinc ions(Zn²⁺)are introduced into PAA solution（denoted as PAA-Zn）,and the interaction between Zn²⁺and-NH₂ weakens the reaction between PAA and non-fullerene acceptors,and the"S"shape in the J-V curve of non-fullerene organic solar cells is eliminated.Based on this method,PAA-Zn has been successfully applied in organic solar cells with PBDB-T:F-M,PM6:IT-4F and PM6:Y6 as active layers.（2）PEDOT:PSS is a conductive polymer,and widely used as an electrode material in printed organic solar cells.However,PEDOT is in an oxidation state,and it is easy to be chemically reduced by cathode interface materials with reducibility,which will change its photoelectric properties.Among the common cathode interface materials,sol-gel Zn O contains ethanolamine molecules,which can easily reduce PEDOT:PSS electrode.Another commonly used interface layer of polyethyleneimine（PEI）,not only contains amine groups,but also is sensitive to film thickness because of its insulating nature.It is difficult to print high-performance low work function polymer electrode based on PEDOT:PSS.In this thesis,zinc ions are introduced into polyethylenimine ethoxylated（PEIE）solution（denoted as PEIE-Zn）,and the coordination between Zn²⁺and amine group（imine group and other groups）weakens the reduction of PEDOT:PSS by PEIE.At the same time,PEIE-Zn also has the advantage of insensitivity to thickness and is suitable for printing on a large scale.Low-work function composite electrode PEDOT:PSS/PEIE-Zn was prepared by blade-coating,and devices were fabricated on the blade-coated PEDOT:PSS/PEIE-Zn electrode.With the active layer of PM6:Y6,the device efficiency was more than 11%.