Research On Design And Synthesis Of Asymmetric Nonfullerene Acceptors And Their Photovoltaic Properties

With the worsening energy problem,organic solar cells,as an emerging technology,have great potential for renewable energy applications owing to their inherent advantages of light weight,flexibility,solution processability and colorfulness etc,.With the advent of non-fullerenes acceptors（NFAs）and the rapid development of device engineering,OSCs have shown an explosive growth in power conversion efficiency（PCE）,currently exceeding 19%for single-section OSCs.However,compared with inorganic and perovskite solar cells,the energy loss(E_loss)of organic solar cells is relatively large,which becomes one of the key factors limiting further breakthroughs in the photovoltaic performance of OSCs.Currently,the energy loss of most high-performance OSCs is generally higher than 0.55 e V.Therefore,reducing the E_lossto obtain a higher open-circuit voltage(V_oc)without sacrificing the short-circuit current(J_sc)and fill factor（FF）is the key to further improve the PCE of OSCs.In this paper,a new asymmetric non-fullerene acceptor（a-NFAs）was designed and synthesized based on the Y-series molecular skeleton by applying the"dual asymmetric strategy",and a high-performance binary and ternary organic photovoltaic device with low E_losswas prepared,which is a guide for the development of solar cells with low E_lossand high performance.The details of this thesis are as follows:1.A new asymmetric molecule SN-O was synthesized by introducing alkoxy-substituted thienothiophene units based on the backbone of the asymmetric molecule SN,by applying the"dual asymmetric strategy".Benefiting from the synergistic effect of alkoxy-substituted thienothiophene and thieno[3,2-b]pyrrole unit,SN-O shows a significant increase in both HOMO and LUMO energy levels.The higher LUMO energy level facilitates the matching with the polymer donor D18 to obtain higher V_oc,and meanwhile,SN-O maintains a HOMO energy level similar to that of D18,which facilitates enhanced hybridization of the local excited and charge transport states,resulting in low non-radiative energy loss and thus low total energy loss.The binary organic solar cell based on D18:SN-O obtained a high V_ocof 0.925 V and an ultra-low non-radiative energy loss(ΔE_nonrad)of 0.177 e V,which is the lowest value ofΔE_nonradfor the high performance D18:NFAs based system.2.Ternary organic solar cells based on D18:Y6:SN-O were prepared.By introducing the asymmetric molecule SN-O into the D18:Y6 binary blend,the ternary OSC exhibited a fairly high PCE of 18.3%and a lowΔE_nonradof 0.202 e V,which was much better than the D18:Y6 binary component(PCE of 17.3%andΔE_nonradof 0.248e V).The improvement in device performance can be attributed to the more ordered molecular stacking,enhanced crystallinity and fiber-like nanostructures in the ternary blend films,which promote exciton dissociation,charge generation and collection.This work further demonstrates the delicate a-NFAs design can significantly reduce the non-radiative energy loss and control the nanomorphology in blend films,thus significantly improve the performance of OSCs.