Design,Synthesis And Properties Of Pyrene-Diimide-Based Cathode Interface Materials

Organic solar cells(OSCs)have attracted the attention of many researchers due to their advantages of light weight,solution-processability and large-scale printability.In recent years,the power conversion efficiency(PCE)of organic solar cells has increased rapidly,and the efficiency of single junction devices has exceeded 19%.In device optimization,constructing an efficient organic cathode interface layer(CIL)is one of the important strategies to improve the efficiency and stability of photovoltaic devices.In this paper,we focus on "improving the performance of binary organic solar cell devices".A series of small molecule and polymer cathode interface materials(CIMs)based on pyrene diimide(Py DI)were designed and synthesized.By adjusting the crystallinity,absorption range,frontier orbital energy level,self-doping ability and morphology of Py DI-based cathode interface materials,organic solar cells with high performance were obtained.Furthermore,the relationship between material structure and device performance was studied by investigating the photovoltaic parameters,charge recombination behaviors and film-thickness tolerances of the devices.These results demonstrate that the CIMs with Py DI conjugated framework might become the vigorous competitor in the field of OSCs.The contents are as follows:In the second chapter,pyrene diimide(Py DI)-based cathode interface materials(Py DIN and t-Py DIN)were constructed for the first time.The results show that the two new self-doped cathode interface materials(Py DIN and t-Py DIN)show good electron extraction ability,and their absorption range is 350-500 nm,which can form good complementary with the commonly used active layer materials,thus broadening the absorption range of the device as well as enhancing the photocurrent of the device.In particular,the introduction of tert-butyl group balanced the crystallinity and filmforming properties of the interface materials.The organic solar cell device with tPy DIN as the cathode interface layer and PM6: Y6 as the active layer obtained the highest power conversion efficiency of 16.82%,which is one of the highest PCE based on PM6: Y6 binary system.In the third chapter,we developed highly efficient cathode interface materials t-Py DINO and t-Py DINBr containing tertiary amine oxide and quaternary ammonium bromide functional groups with t-Py DIN as the basic structure.It was found that the ionized CIMs showed higher alcohol solubility and better filmthickness insensitivity.We employed PM6: BTP-e C9 as the active layer,and used tPy DIN,t-Py DINO and t-Py DINBr as the cathode interface layer to construct organic photovoltaic devices.Among them,the efficiency of the binary device with t-Py DIN as the cathode interface layer can reach 18.25%,which is among the highest efficiencies of the current binary devices.In addition,the ionized cathode interface material tPy DINBr has better alcohol solubility,stronger self-doping characteristics and deeper LUMO energy level than t-Py DIN,thus showing good film thickness insensitivity.When the thickness of the interface layer is about 53 nm,the device can maintain more than 84% of the efficiency under the optimal film thickness,which provides us a way for preparing the film-thickness insensitive cathode interface material.In the fourth chapter,pyrene diimide-based ionene polymers(PPy DIN-C3,PPy DIN-C4 and PPy DIN-C6)were prepared to improve the film forming property of the cathode interface materials.With the enhancement of filmforming ability,the film-thickness sensitivity of CIMs and their corresponding device efficiency have also been greatly improved.Inspired by the work in the third chapter,ionization strategy is beneficial for obtaining a film-thickness insensitive cathode interface material.However,due to the poor film-forming properties of small molecules,the morphology of the interface layer formed by t-Py DINBr cannot meet the requirements of interface contact for efficient devices.In this chapter,we prepared ionene polymer cathode interface materials(PPy DIN-C3,PPy DIN-C4 and PPy DINC6)of pyrene diimide.The main chain ionized polymer interface material is completely orthogonal to the active layer and has good film-forming properties,reducing its filmthickness sensitivity.The cathode interface material PPy DIN-C3 was applied to organic solar cell devices with different thicknesses,and its photovoltaic performance was tested.When the film thickness reached 75 nm,the power conversion efficiency of the device could still maintain 85% of the best efficiency,and the open circuit voltage remained almost unchanged.In the fifth chapter,A-A’ type polymerized ionene cathode interface materials(0.75 PPy DIN,0.50 PPy DIN and 0.25 PPy DIN)were prepared to further broaden the spectral absorption range of pyrene diimide-based cathode interface materials and reduce their LUMO energy levels.We prepared A-A’ type polymerized ionene cathode interface materials by Menschuktin reaction between t-Py DIN and NDI unit with bluer absorption and lower LUMO level,and optimized the properties of the interface materials by optimizing the ratio of t-Py DIN and NDI units.The ionene polymer cathode interface materials constructed by t-Py DIN and NDI have the following advantages: 1)The non-conjugated polymerizing method maintains the light absorption range of NDI and t-Py DI,and resulted in cathode interface materials with wider obsorption range;2)The A-A’ type polymerization allows the molecule to simultaneously obtain lower LUMO and HOMO energy levels,which is conducive to electron transport and inhibits hole accumulation.The device based on cathode interface material 0.75 PPy DIN with PM6: Y6 as the active layer obtained a PCE of16.24%.