Study On Synthesis And Device Performance Of Efficient Organic Small Molecular Donor Materials On The Basis Of "Symmetry Breaking" Strategy

As a new research area in the field of photovoltaic power generation,organic solar cells(OSCs)have shown the strength in low cost,simple structure,solution processable,flexibility and transitsparent compared with traditional silicon solar cells.Being able to used as a supplement to silicon solar cells,OSCs have great application potential in indoor photovoltaic,photovoltaic agriculture,photovoltaic new energy vehicles,etc.However,with the welldefined molecular structure,easy purification and negligible batch-to-batch variations performance,all-small-molecule organic solar cells(ASM-OSCs)have a prospecting future.As an effective molecular structure design method,the "symmetry breaking" strategy can more accurately control the properties of molecular energy levels,molecular stacking and so on.Therefore,this paper mainly uses the "symmetry breaking" strategy to develop a series of small molecule donor materials and fully study their photovoltaic properties.The main research content is as follows:(1)Based on the A-π-D-π-A structure with benzodithiophene(BDT)as the core,two small molecule donor materials named TB and TB-F were designed and synthesized by introducing an asymmetric two-dimensional side chain.Compared with symmetric structures,the use of small molecular donors with asymmetric 2D side chains has significant optimization in terms of crystallinity,molecular filling,blend film morphology and photodynamics.Accrding to the study of morphology and device,TB-F:L8-BO blend film have great penetrating network,higher mobility of charge carrier and favorable ability of electric charge collection.In addition,the joint experimental and theoretical calculations show that the asymmetric donor exhibits stronger molecular interaction between the unilateral phenyl-side chain and the nonfullerene receptor end group,and has better miscibility with L8-BO,thus forming a good flow path for charge transport,and finally achieving 17.0% high efficiency all small molecule organic solar cells(ASM-OSCs).(2)Two novel small molecule donors S-TCp and As-TCp with conjugated symmetric/asymmetric complex cycloamyl hexyl side chains were developed on benzodithiophene(BDT)central units for use in high efficiency all-small molecule organic solar cells(ASM-OSCs).Compared with S-BF,the introduction of heterocyclic amyl hexyl side chains can raise the molecular energy level and slightly reduce the crystallization tendency of As-TCp and S-TCp.This asymmetrically mixed side-chain strategy has a significant impact on molecular interactions,ensuring better molecular assembly and further control of nanoscale bi-continuous interpenetrating networks.Therefore,binary components based on S-TCp and As-TCp exhibit the highest PV performance of 15.77% and 16.46%,respectively,compared with S-BF(14.92%),due to balanced charge transfer,suppressed charge recombination,and favorable phase separation body heterojunction(BHJ)morphology.The introduction of cycloalkyl chains combined with asymmetric 2D side chain strategy is an effective synergistic method to control intermolecular interactions and nanoscale phase separation to achieve high performance ASM-OSCs.