Heteroatom substitution-induced asymmetric A–D–A type non-fullerene acceptor for efficient organic solar cells

Research on asymmetric A–D–A structured non-fullerene acceptors has lagged far behind the development of symmetric counterpart.In this contribution,by simply replacing one sulfur atom in indacenodithiophene unit with a selenium atom,an asymmetric building block Se PT and a corresponding asymmetric non-fullerene acceptor Se PT-IN have been developed.Asymmetric Se PT-IN achieved a high efficiency of 10.20% in organic solar cells when blended with PBT1-C,much higher than that of symmetric TPT-IN counterpart(8.91%).Our results demonstrated an effective heteroatom substitution strategy to develop asymmetric A–D–A structured non-fullerene acceptors.

Enhancing Photovoltaic Performance of Nonfused-Ring Electron Acceptors via Asymmetric End-Group Engineering and Noncovalently Conformational Locks

By employing the asymmetric end-group engineering,an asymmetric nonfused-ring electron acceptor(NFREA)was designed and synthesized.Compared with the symmetric analogs(NoCA-17 and NoCA-18),NoCA-19 possesses broader light absorption range,more coplanarπ-conjugated backbone,and appropriate crystallinity according to the experimental and theoretical results.The organic solar cells based on J52:NoCA-19 exhibited a power conversion efficiency as high as 12.26%,which is much higher than those of J52:NoCA-17(9.50%)and J52:NoCA-18(11.77%),mainly due to more efficient exciton dissociation,better and balanced charge mobility,suppressed recombination loss,shorter charge extraction time,longer charge carrier lifetimes,and more favorable blend film morphology.These findings demonstrate the great potential of asymmetric end-group engineering in exploring low-cost and high-performance NFREAs.

Insight into the efficiency-stability-cost balanced organic solar cell based on a polymerized nonfused-ring electron acceptor

Organic solar cells(OSCs)have attracted extensive attention from both academia and industry in recent years due to their remarkable improvement in power conversion efficiency(PCE).However,the Golden Triangle(the balance of efficiency-stability-cost)required for large-scale industrialization of OSCs still remains a great challenge.Here,a new nonfused-ring electron acceptor(NFREA)BF and its polymerized counterpart PBF were designed and synthesized,and their photovoltaic performance,storage stability and material cost were systematically investigated.When blended with a widely-used polymer donor PBDB-T,the PBFbased all-polymer solar cell(all-PSC)displayed a record high PCE of 12.61%for polymerized NFREAs(PNFREAs)with an excellent stability(95.2%of initial PCE after 800 h storage),superior to the BF counterpart.Impressively,PBF-based allPSC possesses the highest industrial figure-of-merit(i-FOM)value of 0.309 based on an efficiency-stability-cost evaluation,in comparison to several representative OSC systems(such as PM6:Y6 and PBDB-T:PZ1).This work provides an insight into the balance of efficiency,stability,and cost,and also indicates that the PNFREAs are promising materials toward the commercial application of OSCs.

Combination of S…N and S…Cl Noncovalently Conformational Locks for Constructing High-Planarity and Low-Cost Nonfused-Ring Electron Acceptors

Comprehensive Summary By employing thiazole and 4-chlorothiazole as the A′units,two A-D-A′-D-A type nonfused-ring electron acceptors(NFREAs)Tz-H and Tz-Cl were designed and synthesized.Replacing thiazole in Tz-H with 4-chlorothiazole can not only remarkably shorten the synthetic route through C—H direct arylation but also enhance molecular planarity with the simultaneous incorporation of S…N and S…Cl noncovalently conformational locks(NoCLs).The photovoltaic devices based on PM6:Tz-Cl exhibited a power conversion efficiency as high as 11.10%,much higher than that of PM6:Tz-H(6.41%),mainly due to more efficient exciton dissociation,better and more balanced carrier mobility,less charge recombination,and more favorable morphology.These findings demonstrate the great potential of NoCLs in achieving low-cost and high-performance NFREAs.

High-Efficiency and Low-Energy-Loss Organic Solar Cells Enabled by Tuning Conformations of Dimeric Electron Acceptors

Dimeric fused-ring electron acceptors(DFREAs)have attracted much attention due to the combined advantages of their monomeric and polymeric acceptors,including a well-defined molecular structure,excellent repeatability,and stable morphology.However,the additionally introduced single-bonds during dimerization may result in a twisted backbone of DFREAs,which is detrimental to intermolecular packing and charge transport.Herein,three DFREAs are designed and synthesized,in which DFREA conformations were systematically tuned via adjusting the intensities of intramolecular noncovalent interactions(INIs)to achieve high-performance organic solar cells(OSCs).Theoretical and experimental results show that the gradual introduction of S…F INIs can continuously improve molecular planarity and rigidity,resulting in reduced reorganization energies,ordered packing mode,and enhanced crystallization of DFREAs.Benefiting from the incorporation of fourfold S…F INIs,DYF-TF-based binary OSCs show a record high efficiency of 18.26%with an extremely low energy loss(0.493 eV)for DFREAbased OSCs.In addition,DYF-TF-based OSCs exhibited good long-term stability with a T_(80%)lifetime of 2681 h,and the power conversion efficiency of the DYF-TF-based ternary device is further enhanced to 18.73%.This contribution demonstrates the great potential of the INIs strategy in achieving excellent DFREAs materials.

Improvement of photovoltaic properties of benzo[1,2-b:4,5-b′]difuran-conjugated polymer by side-chain modification

The development of polymer solar cells(PSCs)for the donor materials based on benzo[1,2-b:4,5-b′]dithiophene(BDT)has significantly boosted the power conversion efficiency(PCE).However,the PCE of polymer donor materials for benzo[1,2-b:4,5-b′]difuran(BDF)-based lags far behind that of their BDT analogs.To further explore efficient copolymers based on BDF units,a two-dimensional(2D)side-chain strategy was proposed to investigate the atom-changing effects on the copolymer donors for the properties of electron and optical.In this study,we designed and synthesized three new BDF-based copolymer donor materials,named PBDF-C,PBDF-O,and PBDF-S.Owing to the balanced charge transport and favorable phase separation of PBDF-S:Y6,a high PCE of 13.4%,a short-circuit current(J sc)of 25.48 mA cm−2,an open-circuit voltage(V oc)of 0.721 V,and a fill factor(FF)of 72.6%was obtained.This research demonstrates that the BDF building block has great potential for constructing conjugated copolymer donors for high-performance PSCs and that 2D side-chain modification is a facile approach for designing high-performance BDF-based copolymer materials.

Optimal bulk-heterojunction morphology enabled by fibril network strategy for high-performance organic solar cells

A bicontinuous network formed spontaneously upon film preparation is highly desirable for bulk-heterojunction(BHJ) organic solar cells(OSCs). Many donor-acceptor(D-A) type conjugated polymers can self-assemble into polymer fibrils in the solid state and such fibril-assembly can construct the morphological framework by forming a network structure, inducing the formation of ideal BHJ morphology. Our recent works have revealed that the fibril network strategy(FNS) can control the blend morphology in fullerene, non-fullerene and ternary OSCs. It has been shown that the formation of fibril network can optimize phase separation scale and ensure efficient exciton dissociation and charge carriers transport, thus leading to impressive power conversion efficiencies(PCEs) and high fill factor(FF) values. We believe that FNS will provide a promising approach for the optimization of active layer morphology and the improvement of photovoltaic performance, and further promote the commercialization of OSCs.

High-efficiency organic solar cells enabled by an alcohol-washable solid additive

The solvent additive strategy has been widely utilized to boost the power conversion efficiency(PCE)of organic solar cells(OSCs).However,the residual solvent additive in the active layer tends to induce a gradual morphology degradation and further influences the long-term stability of OSCs.Here,a solid additive,1,4-diiodobenzene(DIB),was introduced to fabricate efficient OSCs.We found that the treatment of DIB can lead to optimized morphology to form a bicontinuous network with intensified intermolecular packing in the donor and acceptor phases.Notably,DIB can be easily removed from the active layer via a simple alcohol washing process and no further post-thermal annealing is needed,which is desirable for large-scale manufacturing of OSCs.As a result,high efficiencies of 17.47%for PM6:Y6 and 18.13%(certified as 17.7%)for PM6:BTP-eC9 binary OSCs are achieved,which are among the highest efficiencies reported for binary OSCs thus far.Moreover,OSCs fabricated with DIB also exhibit superior stability compared with the as-cast and traditional solvent additive processed devices.Additionally,DIB was successfully applied in different active layers,manifesting its general applicability.This work provides a feasible approach to enhance both the efficiency and stability of OSCs.

Organic solar cells based on chlorine functionalized benzo[1,2-b:4,5-b′]difuran-benzo[1,2-c:4,5-c′]dithiophene-4,8-dione copolymer with efficiency exceeding 13%

Benzo[1,2-b:4,5-b′]dithiophene(BDT) has been widely used to construct donor-acceptor(D-A) copolymers in organic solar cells(OSCs). However, benzo[1,2-b:4,5-b′]difuran(BDF), an analogue of BDT, has received less attention than BDT. The photovoltaic performance of BDF copolymers has lagged behind that of BDT copolymers. Here, we designed and synthesized two BDF copolymers, PBF1-C and PBF1-C-2Cl. PBF1-C-2Cl, which is composed of BDF and benzo[1,2-c:4,5-c′]dithiophene-4,8-dione connected by a chlorinated thiophene π-bridge, displays a low-lying highest occupied molecular orbital energy level,which helps in yielding a high open-circuit voltage(Voc) in OSCs. As a result, when blended with Y6, PBF1-C-2Cl-based devices showed a high Voc of 0.83 V and a power conversion efficiency(PCE) of 13.10%. To the best of our knowledge, the PCE of 13.10% is among the highest efficiency values for OSCs based on BDF copolymers.