Research On Photoactive Cathode Interlayer Materials For Nonfullerene Organic Solar Cells

In recent years,with the rapid development of non-fullerene acceptors materials,the power conversion efficiency of organic solar cells has been improved rapidly.However,the current cathode interlayer is still using the traditional cathode interlayer materials developed for fullerene materials,and there is no systematic study on the interface engineering according to the characteristic of non-fullerene system.In the process of rapid development,scientists gradually realized the significance of manufacturing and stability of the devices,which is challenging for commercialization in the future.The cathode interlayer materials have crucial effect on the stability of devices and high transporting properties will also promote better performance.Therefore,in order to develop new highly efficient interlayer materials system and further promote the application of organic photovoltaic,it is urgent to develop new cathode interlayer materials in this field.In this thesis,the above problems of organic solar cells have been systematically studied.To solve the key problems of classical cathode modification materials,such as low conductivity,we developed a novel photoactive materials Zn O:HO-PBI by doping the dye molecules perylene bisimide(PBI)into metal oxide(Zn O)thin film,which improved the conductivity of interlayer by successful photoinduced electron transfer.The uniform doping distribution of organic dyes in bulk of Zn O thin film is the key to achieve photoconductivity at a low concentration of dopant.Herein,we design the PBI structure by introducing hydroxylation in the bay position of perylene,and deprotonation effect helps form the chelating coordination between Zn and dye molecules.The organic-inorganic hybrid Zn O:HO-PBI photoconductive cathode interlayer was used in inverted organic solar cells and electron collection and electron transporting of devices were improved,which leads to power conversion efficiency of 15.9%.Due to the low crystallization temperature of sol-gel derived Zn O thin films,the Zn O will have many structural residual electron defects and high temperature(>250°C)is needed to improve the crystalline and reduce the density of defects,which limit the application on flexible devices and modules.To solve the low temperature processing problem of Zn O,we introduced several carboxyl groups into molecules(PBI-COOH),which easily forms coordination bonds with Zn atom at room temperature.The dye molecules were dissolved in the precursor solution for the preparation of Zn O and formed coordination with Zn atom in solution and then the solution was further used to fabricate hybrid thin films.The results show that the hybrid interlayer with high photoconductivity can be obtained under 130°C,which meets the required for flexible plastic substrates.Owing to photoinduced electron transfer effect,the electron mobility of Zn O:PBI-COOH films reach 9.50×10^-4 cm² V^-1 s^-1,and conductivity is significantly improved compared with that of pure Zn O films under illumination.The flexible solar cells were fabricated by using the low temperature processed method,with power conversion efficiency reached 9.63%.Non-fullerene acceptors are easy to be photo-oxidized and decomposed in air ambient and typical amino-containing cathode interlayer materials will accelerate the degradation of acceptors,which is the origin of poor device stability.Herein,a novel cathode interlayer did not contain amines or ammonium salts was developed by introducing phenol groups which can easily form biradicals under luminescence.The two di-tert-butyl phenol substituents with antioxidant function at bay position of perylene improved the solubility of molecules(PBI-2P)in methanol,moreover,the intramolecular push-pull structure enhance the stability of phenolic biradicals by open-shell structure.Compared with typical materials with amino-functional groups(PEIE),the blends of PBI-2P and Y6 have excellent stability under light conditions in air and light conditions.In addition,devices comprised PBI-2P interlayer reached efficiency value of 17.20%,which also showed better devices stability compared with PEIE-based devices.Furthermore,an ionic perylene imide(PBI-P)with near-infrared(NIR)absorption was formed by the organic base n-type ionic doping.The n-doped PBI-P molecule formed anions at the phenol hydroxyl groups,and then NIR-induced anion-?electron transfer between the anion and the perylene imide skeleton was formed,which generates strong absorption at around 1200nm.In addition,this kind of ionic doped thin film can be stable in the air.Moreover,the photocurrent response of the ionic NIR photoconductive layer is demonstrated by the organic field effect transistor(OFET),and we successfully employ it as cathode interlayer in conventional organic solar cells,which provides a new idea for the novel photoconductive materials.In conclusion,this thesis focused on the scientific problems on non-fullerene organic solar cells and developed interlayer based on perylene bisimide system with good thermal&light stability,photoactive,ionic coordination,radical properties,etc.A series of novel photoactive cathode interlayer materials were studied to solve the significant point of low conductivity,and explored the stability of non-fullerene photovoltaic from the perspective of cathode modification,which provides new idea and thinking in this research area.