Design,synthesis And Photovoltaic Properties Of Non-fused Ring Small Molecule Acceptors Based On Thiophene Derivatives

In recent years,organic solar cells（OSCs）have made significant progress in photovoltaic performance and shown the potential to be the next generation of commercial solar cells.The active layer for OSCs plays an important role to improve their efficiencies,the development of organic electron-accepting materials is a feasible approach to optimize active layer performance.Compared to traditional fullerene acceptors,non-fullerene acceptors（NFAs）have gained tremendous attention due to their superior performance,including tunable performance,low cost,and high stability.This thesis will focus on the design,synthesis,and their application for OSCs’active layer,the details were shown as following.Firstly,the target compounds of BED with short-side chain of 2-ethylhexane and BHD with long-side chain of 7-momethylpentadecane,were designed and synthesized with BDT12 as the core,CPT30 and Br as end groups,and isooctane or 7-methylpentadecane as the side chains.In the meanwhile,the compound of DBD with"full conformation lock"symmetrical structure was designed and synthesized by using IDT30 as the core,BDT12 as the conjugated bridge,CPT30 as the end group,and isooctane as the side chain.Gaussian16 software was used to perform theoretical simulation on the structure of the target compounds,which was to verify the feasibility of the synthetic targe structure.Then,the corresponding structures of them were identified by ¹H NMR and the specially functional groups were further confirmed by infrared spectroscopy.The absorptive properties of the synthesized products were determined by using UV-Vis spectrophotometry.According to the onset of the absorption boundary,the calculated band gaps of BED and BHD were determined to be～1.77 e V,and that of DBD was～1.55 e V.The electrochemical properties of the synthesized compounds were evaluated based on the measurements of cyclic voltammetry.The corresponding HOMO values of BED/BHD and DBD were found to be～5.46 e V,～5.47e V,and～5.6 e V,respectively,while the LUMO values were～3.69 e V,～3.7 e V,and～4.05 e V,respectively.These results demonstrate that the synthesized products BED,BHD,and DBD have potentials for the exploition on the organic solar cells for acceptors.Notably,the energy levels of BED,BHD,and DBD are similar to those of PM6 and Y6,which have HOMO levels of 5.54、5.62 e V,and LUMO levels of 3.61、4.11 e V.Secondly,the synthesized products BED and BHD were added as the third component as acceptor materials into the PM6:Y6 layer,The fabricated photovoltaic cells have the configuration of ITO/PEDOT:PSS/PM6:Y6 with or without BED and BHD/PDIN/Ag.By introducing the BED and BHD as the third component,it can be seen that the devices with BED/BHD exhibit higher PCEs compared to the control devices without BED and BHD.Noticably,BHD was added into the active layer of PM6:Y6.The device showed the best photovoltaic performance with a short circuit current(J_SC)of 26.79 m A·cm^-2,open circuit voltage(V_OC)of0.845 V,fill factor（FF）of 73.34%,and power conversion efficiency（PCE）of 16.6%.In order to explain the phenomena of improved properties of devices based on BHD,the corresponding characterizations were carried out,including light intensity dependence,dark current density-voltage,current impedance,voltage-current,and external quantum efficiency.The results showed that the promoted exciton dissociation and inhibited charge recombination were observed by introducing BHD into PM6:Y6 as the third component as acceptor.Our results provide a feasible strategy for the development of the third component acceptors with a simple structure and efficient photovoltaic performance.Finally,the photovoltaic devices with the structure of ITO/PEDOT:PSS/PM6:Y6 with or without DBD/PDIN/Ag were constructed by using the synthesized DBD as similar acceptor into PM6:Y6.When the concentration of DBD is～0.25%,it was obvious that the efficiencies was significantly improved.The value of PCE increases from 15.8%to 16.25%with a J_SC of 26.77 m A·cm^-2,a V_OC of 0.853 V,and a FF of 71.15%,respectively.Similarly,the series of measurements were done,including light intensity dependence,dark current density-voltage,current impedance,voltage-current,and external quantum efficiency.Due to the slightly mismatched energy levels of DBD,PM6 and Y6,Fore the addition of DBD,its performance is less that that of BED and BHD.Further optical and electrical tests on devices showed the limited inhibition of charge recombination.However,it could still slightly improve exciton dissociation due to the results of light intensity measurements,which was still helpful to improve the device performance.