Near-infrared non-fused electron acceptors for efficient organic photovoltaics

Developing narrow-bandgap organic semiconductors is important to facilitate the advancement of organic photovoltaics(OPVs). Herein, two near-infrared non-fused ring acceptors(NIR NFRAs), PTBFTT-F and PTBFTT-Cl have been developed with A-π_A-π_D-D-π_D-π_A-A non-fused structures. It is revealed that the introduction of electron deficient π-bridge(π_A) and multiple intramolecular noncovalent interactions effectively retained the structural planarity and intramolecular charge transfer of NFRAs, extending strong NIR photon absorption up to 950 nm. Further, the chlorinated acceptor, with the enlarged π-surface compared to the fluorinated counterpart, promoted not only molecular stacking in solid, but also the desirable photochemical stability in ambient, which are helpful to thereby improve the exciton and charge dynamics for the corresponding OPVs. Overall, this work provides valuable insights into the design of NIR organic semiconductors.

Enhancing efficiency and stability of organic solar cells through a simplified four-step synthesis of fully non-fused ring electron acceptor

Design and synthesis of superior cost-effective non-fullerene acceptors(NFAs)are still big challenges for facilitating the commercialization of organic solar cells(OSCs),yet to be realized.Herein,two medium bandgap fully non-fused ring electron acceptors(NFREAs,medium bandgap,i,e.,1,3-1,8 eV),namely PTR-2Cl and PTR-4Cl are synthesized with only four steps by using intramolecular noncovalent interaction central core,structured alkyl side chain orientation linking units and flanking with different electron-withdrawing end group.Among them,PTR-4C1 exhibits increased average electrostatic potential(ESP)difference with polymer donor,enhanced crystallinity and compactπ-πstacking compared with the control molecule PTR-2CI.As a result,the PTR-4Cl-based OSC achieved an impressive power conversion efficiency(PCE)of 14.72%,with a much higher open-circuit voltage(V_(OC))of 0.953 V and significantly improved fill factor(FF)of 0.758,demonstrating one of the best acceptor material in the top-performing fully NFREA-based OSCs with both high PCE and V_(OC).Notably,PTR-4Cl-based cells maintain a good T_80lifetime of its initial PCE after over 936 h under a continuous thermal annealing treatment and over1300 h T_(80)lifetime without encapsulation.This work provides a cost-effective design strategy for NFREAs on obtaining high V_(OC),efficient exciton dissociation,and ordered molecular packing and thus high-efficiency and stable OSCs.

Regioregular Non-Fused Polymerized Small Molecular Acceptors Enabling Efficient All-Polymer Solar Cells

Comprehensive Summary The regioregularity induced by the isomers of the end-groups has been widely recognized as a key factor that determines the photovoltaic properties of polymerized small molecular acceptors(PSMAs)in all-polymer solar cells(all-PSCs).However,the influence of regioregularity on the photovoltaic properties of non-fused PSMAs has not been explored yet.In this contribution,two regioregular non-fused PSMAs,PFBTz-T-γand PFBTz-T-δ,were synthesized for the first time by using the monomers with isomeric pure end-groups.Compared with PFBTz-T-δ,PFBTz-T-γhas more compact and more ordered packing in solid state,which results in a more red-shifted optical absorption and a higher electron mobility.More remarkably,PFBTz-T-γand PFBTz-T-δexhibited huge difference in photovoltaic performance in all-PSCs,which offered the power conversion efficiencies(PCEs)of 9.72%and 0.52%,respectively.Further studies have unveiled that the higher PCE of PFBTz-T-γis due to more efficient exciton dissociation,higher and more balanced electron/hole mobility,and less charge recombination as a result of favorable morphology of the blend film.This work demonstrates that the development of regioregular non-fused PSMAs by tuning the polymerization sites is an effective strategy for obtaining high-efficiency all-PSCs.

Low-cost organic photovoltaic materials with great application potentials enabled by developing isomerized non-fused ring acceptors

Benefitting from low cost and simple synthesis,simple structured non-fused ring acceptors(NFRAs)and polymer donors are crucial for the application of organic solar cells(OSCs).Herein,two isomerized NFRAs,namely 4T-FCl FCl and 4T-2F2Cl,are designed with end-group engineering,which modulates the electrostatic potential distributions and crystallinity of acceptors,and accordingly,the A/A and D/A intermolecular interactions.The OSC based on 4T-2F2Cl with strong D/A interactions shows a record-high efficiency of 16.31%in blending with a low-cost polymer donor PTQ10,which shapes obviously improved bulkheterojunction(BHJ)networks blade-coated by non-halogenated solvent o-xylene,and thus significantly diminishes nonradiative recombination loss.A higher industrial figure of merit(i-FOM)of 0.46 for PTQ10:4T-2F2Cl in comparison with PTQ10:4T-FCl FCl(i-FOM=0.29)is demonstrated owing to its superior device efficiency and operational stability.Note that the i-FOM of PTQ10:4T-2F2Cl is the highest value for OSCs reported so far.This work deepens the synergistic effect of the A/A and D/A interactions on achieving desired bulk heterojunction morphology and demonstrates a printable photovoltaic system for low-cost,high-efficiency,stable,and eco-friendly OSCs.

Latest progress on fully non-fused electron acceptors for high-performance organic solar cells

Benefitting from the development of non-fullerene acceptors(NFAs),remarkable advances have been achieved with the power conversion efficiency(PCE)exceeding 19%over the last few years.However,the major achievement comes from fused ring electron acceptors(FREAs)with complex structures,leading to high cost.Hence,it is urgent to design new materials to resolve the cost issues concerning basic commercial requirements of organic solar cells.Recently,great progress has been made in fully non-fused ring electron acceptors(NFREAs)with only single-aromatic ring in the electron-donating core,which might achieve a fine balance between the efficiency and cost,thus accelerating the commercial application of organic solar cells.Therefore,this article summarizes the recent advances of fully NFREAs with efficiency over 10%,which may provide a guidance for developing the cost-effective solar cells.

Carbazolebis(thiadiazole)-core based non-fused ring electron acceptors for efficient organic solar cells

Non-fused ring electron acceptors(NFREAs)have a broad application prospect in the commercialization of organic solar cells(OSCs)due to the advantages of simple synthesis and low cost.The selection of intermediate block cores of non-fused frameworks and the establishment of the relationship between molecular structure and device performance are crucial for the realization of high-performance OSCs.Herein,two A-D-A’-D-A type NFREAs namely CBTBO-4F and CBTBO-4Cl,constructed with a novel electron-deficient block unit N-(2-butyloctyl)-carbazole[3,4-c:5,6-c]bis[1,2,5]thiadiazole(CBT)and bridging unit 4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b’]dithiophene(DTC)coupling with different terminals(IC-2F/2Cl),were designed and synthesized.The two NFREAs feature broad and strong photoresponse from 500 nm to 900 nm due to the strong intramolecular charge transfer characteristics.Compared with CBTBO-4F,CBTBO-4Cl shows better molecular planarity,stronger crystallinity,more ordered molecular stacking,larger van der Waals surface,lower energy level and better active layer morphology,contributing to much better charge separation and transport behaviors in its based devices.As a result,the CBTBO-4Cl based device obtains a higher power conversion efficiency of 10.18%with an open-circuit voltage of 0.80 V and a short-circuit current density of 21.20 mA/cm^(2).These results not only demonstrate the great potential of CBT,a new building block of the benzothiazole family,in the construction of high-performance organic conjugated semiconductors,but also suggest that the terminal chlorination is an effective strategy to improve device performance.

An asymmetric non-fused electron-deficient building block for low-cost polymer acceptor in all-polymer solar cells

The development of polymerized fused-ring small molecule acceptors(FRA-PAs) has boosted the performance of all-polymer solar cells(all-PSCs).However,these FRA-PAs suffer from lengthy synthesis steps and high production costs due to the high degree of synthetic complexity for fused-ring small molecule acceptors(FRAs).Furthermore,most FRA-PAs exhibit strong batch-to-batch variation,limiting further industrial applications.Herein,we designed and synthesized asymmetric non-fused electron-deficient building block TIC-Br with a simple structure(only three synthetic steps),showing a planar configuration,excellent electron affinity,and large dipole moment.A simple polymer acceptor PTIB was further developed by polymerization of TIC-Br and sensitized fluorinated-thienyl benzodithiophene(BDT-TF-Sn).PTIB exhibits a broad absorption from 300 to 800 nm,a suitable lowest unoccupied molecular orbital(LUMO) energy level of-3.86 e V,and moderate electron mobility(1.02×10^(-4)cm^(2)V^(-1)s^(-1)).When matched with PM6,the device achieved the best PCE of 10.11%with a high V_(OC) of 0.97 V,which is one of the highest among those reported all-PSCs.More importantly,PTIB exhibits a lower synthetic complexity index(SC=35.0%)and higher figure-of-merit values(FOM=29.0%) than all the reported high-performance PAs.The polymer also exhibits excellent batch-to-batch reproducibility and great potential for scale-up fabrication.This study indicates that TIC-Br is a promising building block for constructing low-cost polymer acceptors for large-scale applications in all-PSCs.

Unaxisymmetric Non-Fused Electron Acceptors for Efficient Polymer Solar Cells

To develop photovoltaics embracing the both features of high performance and low cost has drawn attentions of researchers,yet representing the significant challenges.In this work,two non-fused ring acceptors(NFRAs),namely p-PTIC4Cl and t-PTIC4Cl,were developed via a short synthetic route.By tethering unaxisymmetric aromatic chains to thienyl bridge of NFRAs,we revealed that the tuning of aromatic chains allows modulating the self-assembly and stacking of NFRAs in solid,hence influencing their optoelectronic and photovoltaic properties.As results,p-PTIC4Cl,consisting of 3-hexylbenzene with large axial angle to backbone,can achieve superior PCE of 11.30%than that of t-PTIC4Cl with 2-hexylthiophene chains(PCE of 6.49%),when pairing with polymer donor PBDB-TF.Despite of the only subtle structural difference,the p-PTIC4Cl based blend films possess better exciton dissociation and charge transfer rates,as well as photostability,to those of t-PTIC4Cl based blends.

Design and Synthesis of N-Alkylaniline-Substituted Low Band-Gap Electron Acceptors for Photovoltaic Application

A novel electron donating unit,namely N-octyl-N-phenyl-thiophene(OPT),was designed in preparing electron acceptors with non-fused ring chemical structures.By introducing different functional atoms/groups into the para-position of phenyl in the OPT units,three non-fused ring acceptors(NFREAs),C8-2F,FC8-2F and MeC8-2F,were synthesized.The absorption spectrum of the three acceptors can be extended to about 950 nm with band-gaps of 1.28—1.32 eV due to the strong electron donating ability of OPT.The frontier molecular orbital distribution of OPT based molecules obtained by quantum chemistry calculation results reveals that their energy alignment can be finely tuned to meet different requirements.Moreover,by changing the substituents on the OPT units,their Flory-Huggins interaction parameter(χ)with the donor will be greatly influenced and different phase separation behavior can be accomplished.After blended with PBDB-TF,the FC8-2F-based cell yields short circuit current density(J_(sc))of 23.21 mA·cm^(-2),fill factor(FF)of 72.11%and the highest power conversion efficiency(PCE)of 12.42%.This work provides a new pathway for molecular design of new NFREAs,and demonstrates the application potential of OPT unit in realizing low band-gap photovoltaic materials.

Formability of Ti-1023 Alloys Fabricated by Direct Laser Deposition

Formability of direct laser deposited Ti-1023 alloys was revealed through investigating the pore defects,microstructure and tensile properties.The results show that gas pores and local non-fusion are two typical defects in the Ti-1023 alloy deposits.Gas pores are spherical and exist randomly in the deposited layers.Non-fusion defects present irregular and lie in adjacent layer-layer and pass-pass boundaries.The layer boundary effects are gradually weakening from the bottom to the top of the single pass deposits.The microstructure of the single pass deposits and multiple pass built block consists of equiaxed grains.Moreover,the tensile properties of as-deposited Ti-1023 alloys are equal to the as-forged tensile corresponding values.Through optimizing the laser rapid forming parameters,the non-fusion defects can be eliminated and the dense Ti-1023 parts are obtained.

通过侧链工程提高A-D-A'-D-A型非稠环电子受体的光伏性能

非稠环电子受体(NFREA)具有合成简单和结构修饰灵活的特点,是制备高性能低成本有机太阳电池(OSCs)的理想材料.本工作以不同侧链修饰的二氟苯并三氮唑(ffBTz)作为弱缺电子核(A’),分别设计合成了三种A-D-A’-D-A型NFREA,即ffBTz-BO、ffBTz-EH和ffBTz-C4.其中,ffBTz-EH,由于其合适的侧链长度,在分子结晶度和分子堆积优势取向之间取得了平衡,从而获得了更高的电荷迁移率.并且得益于高效的电荷传输和最合适的相分离形貌,基于ffBTz-EH的OSC获得12.96%的最高能量转换效率,这也是A-D-A’-D-A型NFREA获得的最高效率之一.本研究表明,A’核心上的烷基侧链在调节分子结晶度、活性层形貌和进一步调控器件性能方面起着至关重要的作用,这为未来设计高效低成本的A-D-A’-D-A型非稠环电子受体提供了思路.