Optimizing Active Layer Materials Synthesis Methods To Construct High-performance Organic Photovoltaic Devices

With the continuous growth of global energy demand and the urgent need for renewable energy,organic solar cells,as an emerging solar energy conversion technology,have outstanding advantages such as simple structure,light weight,low cost,and large-area preparation,especially light,thin,and flexible properties are difficult to possess in inorganic solar cells,which have attracted widespread attention and research from academia and the market.However,the current structural innovation of donor/acceptor units has highlighted development bottlenecks.Complex and cumbersome molecular construction not only has high development costs,but also has great uncertainty in target performance,making the development of high-performance donor/acceptors increasingly difficult.Therefore,avoiding the extremely difficult and uncertain molecular reconstruction and using simple methods to further improve device performance based on the existing active layer based on high-performance polymer materials has gradually become a research focus.This thesis further optimizes simple and efficient ternary copolymerization,ternary blending and designs block copolymer strategies in order to optimize light absorption,film morphology,and molecular energy levels.We designed and synthesized terpolymers and the third component of the oligomer based on PM6,and block copolymers with Y series structure as the acceptor unit as the active layer materials.It aims to further improve device efficiency and stability on the basis of highperformance donor and acceptor materials,and obtain efficient and stable OSCs.The specific research content is as follows:(1)Through a simple ternary copolymerization strategy,a series of polymer donors were designed and synthesized(PM6,PM6-Si Cl-10%,PM6-Si Cl-15%,and PM6-Si Cl-20%).By introducing Si and Cl functionalized benzodithiophene(BDTSi Cl)into a polymer PM6 matrix with F functionalized benzodithiophene(BDT-2F)by random copolymerization.BDT-Si Cl has the same skeleton as BDT-2F,but only differs in functional atoms on the side chain.The structural similarity of the two building blocks not only can minimize the disturbance of the molecular orderly packing caused by random copolymerization,but also can enhance the face-on orientation of the active layer to facilitate charge transport.Moreover,the alkylsilyl and chlorine atom enable the terpolymers to have a lower HOMO level and broadened light absorption compared to PM6.As a result,the terpolymer-based OSCs achieve the best efficiency of 16.22% with a small energy loss of 0.50 e V,yielding overall improved device parameters compared to PM6-based devices.In addition,thanks to the covalent bond linkage the third unit,the terpolymer-based device has a higher thermal stability than its corresponding ternary OSC.(2)Although ternary organic solar cells(OSCs)have unique advantages in improving device performance,the morphology assembly in the ternary-phase would be more uncertain or complex than that in the binary-phase.Here,we propose a new concept of oligomer-assisted photoactive layers for high-performance OSCs.It combines the advantages of ternary and binary systems,and uses the structural similarity and performance complementarity between oligomers and host polymers to regulate the performance of the active layer.A series of oligomers based on PM6 host polymers were designed and synthesized: dimer DA,trimer ADA,DAD and tetramer DADA,and were added to the active layer as the third component.Studies have shown that blending these oligomers with PM6 can effectively reduce the HOMO energy level,enhance light absorption,and form an alloy phase with PM6,inducing the active layer to form stronger π-π stacking.By adding oligomers,PM6:Y6 devices,PM6:BTP-e C9 devices and PM6/Y6 pseudo-planar heterojunction devices achieved device efficiencies of 17.33%,18.32% and 17.13% respectively,and device stability was also improved.These results indicate that the oligomer-assisted photoactive layer strategy is an effective way to achieve efficient and stable organic solar cells.(3)Single-component organic solar cells(SCOSCs)based on conjugated block copolymers(CBCs)by covalently bonding a polymer donor and polymer acceptor become more and more appealing due to the formation of a favorable and stable morphology.Unfortunately,a deep understanding of the effect of the assembly behavior caused by the sequence structure of CBCs on the device performance is still missing.Herein,from the aspect of manipulating the sequence length and distribution regularity of CBCs,we synthesized a series of new CBCs,namely D18(20)-b-PYIT,D18(40)-b-PYIT and D18(60)-b-PYIT by two-pot polymerization,and D18(40)-bPYIT(r)by traditional one-pot method.It is observed that precise manipulation of sequence length and distribution regularity of the polymer blocks fine-tunes the selfassembly of the CBCs,optimizes film morphology,improves optoelectronic properties,and reduces energy loss,leading to simultaneously improved efficiency and stability.Among these CBCs,the D18(40)-b-PYIT-based device achieves a high efficiency of 13.4% with enhanced stability.More importantly,the film-forming kinetics reveals that compared to the corresponding binary blend,CBC with the regular sequence distribution and suitable sequence length can suppress excessive self-aggregation while shorten film-forming time by BC method,enabling a facile filmforming process with good mechanical property.Eventually,impressive efficiencies of 11.62% and 10.73% are achieved in the large-area rigid and flexible devices based on D18(40)-b-PYIT,respectively.(4)Single-component organic solar cells(SCOSCs)with covalently bonding donor and acceptor are becoming increasingly attractive because of their superior stability over traditional multicomponent blend organic solar cells(OSCs).Nevertheless,the efficiency of SCOSCs is far behind the state-of-the-art multicomponent OSCs.Herein,by combination of the advantages of three-component and single-component devices,this work reports an innovative three-in-one strategy to boost the performance of SCOSCs.In this three-in-one strategy,three independent components(PM6,D18,and PYIT)are covalently linked together to create a new single-component active layer based on ternary conjugated block copolymer(TCBC)PM6-D18-b-PYIT by a facile polymerization.Precisely manipulating the component ratios in the polymer chains of PM6-D18-b-PYIT is able to broaden light utilization,promote charge dynamics,optimize,and stabilize film morphology,contributing to the simultaneously enhanced efficiency and stability of the SCOSCs.Ultimately,the PM6-D18-b-PYIT-based device exhibits a power conversion efficiency(PCE)of14.89%,which is the highest efficiency of the reported SCOSCs.Thanks to the aggregation restriction of each component and chain entanglement in the three-in-one system,the PM6-D18-b-PYIT-based SCOSC displays significantly higher stability than the corresponding two-component(PM6-D18:PYIT)and three-component(PM6:D18:PYIT).These results demonstrate that the three-in-one strategy is facile and promising for developing SCOSCs with superior efficiency and stability.