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.

Efficient ternary organic solar cells with high absorption coefficient DIB-SQ as the third component

A series of organic solar cells(OSCs)are prepared with PTB7:PC71 BM as the host materials and DIB-SQ as the third component.The power conversion efficienty(PCE)of OSCs can be improved from 6.79%to 7.92%by incorporating 6 wt%DIB-SQ into donors,resulting from the enhanced short circuit current density(J_(SC))and fill factor(FF).The increased JSCof the optimized ternary OSCs should be attributed to the enhanced photon harvesting of teranry active layer by incorporating DIB-SQ.Meanwhile,FF of the optimized ternary OSCs should be due to the optimied phase separation.The open circuit voltage(V_(OC))of tenray OSCs can be maintained at a constant of 0.75 V,indicating that all photogenerated holes willl be transported along the channels formed by PTB7.

Ternary organic solar cells offer 14% power conversion efficiency

Organic solar cells （OSCs） have advantages like light-weight, flexibility, colorfulness and solution processability [1 ]. The active layer of OSCs generally contains two organic semiconductors： an electron donor and an electron acceptor. The donor and acceptor make nanoscale phase separation to allow efficient exciton dissociation and also form a three-dimensional （3D） passage to rapidly transfer free charge carriers to respective electrodes.

P-doped all-small-molecule organic solar cells with power conversion efficiency of 17.73%

All-small organic solar cells(ASM OSCs)inherit the advantages of the distinct merits of small molecules,such as well-defined structures and less batch-to-batch variation.In comparison with the rapid development of polymer-based OSCs,more efforts are needed to devote to improving the performance of ASM OSCs to close the performance gap between ASM and polymer-based OSCs.Herein,a well-known p-dopant named fluoro-7,7,8,8-tetracyano-p-quinodimethane(FTCNQ)was introduced to a highefficiency system of HD-1:BTP-e C9,and a high power conversion efficiency(PCE)of 17.15%was achieved due to the improved electrical properties as well as better morphology of the active layer,supported by the observed higher fill factor(FF)of 79.45%and suppressed non-radiative recombination loss.Furthermore,combining with the further morphology optimization from solvent additive of 1-iodonaphthalene(IN)in the blend film,the HD-1:BTP-e C9-based device with the synergistic effects of both FTCNQ and IN demonstrates a remarkable PCE of 17.73%(certified as 17.49%),representing the best result of binary ASM OSCs to date.

Semitransparent organic solar cells with high light utilization efficiency and color rendering index

Semitransparent organic solar cells(ST-OSCs)have garnered considerable attention as promising renewable energy technology for integrating photovoltaics into buildings.However,there is a trade-off between power conversion efficiency(PCE)and average visible transmittance(AVT),which hinders the achievement of a high light utilization efficiency(LUE).In this study,we propose a valuable method to address this challenge by replacing the transparent top electrode,Ag,with a 20 nm layer of Au.The ST-OSCs based on the 20 nm Au electrode demonstrate superior exciton extraction,more efficient charge collection,and higher color-rendering index(CRI)due to their smoother surface,higher conductivity,and enhanced visible light transmittance,resulting in a significantly higher PCE of 13.67%and an enhanced AVT of 30.17%,contributing to a high LUE of 4.15%.Additionally,optically transparent dielectric layers,applied on the front and back sides of the ST-OSCs to further boost performance,delivered an impressive LUE of 4.93%,with PCE and AVT values reaching 14.44%and 34.12%,respectively.Notably,the champion ST-OSCs also exhibited a favorable CRI value of 93.37.These achievements represent the bestperforming ST-OSCs to date with both high LUE and CRI and hold significant implications for the prospective commercialization of ST-OSCs.

Side-chain symmetry-breaking strategy on porphyrin donors enables high-efficiency binary all-small-molecule organic solar cells

Side-chain symmetry-breaking strategy plays an important role in developing photovoltaic materials for high-efficiency all-small-molecule organic solar cells(ASM OSCs).However,the power conversion efficiencies(PCEs)of ASM OSCs still lag behind their polymer-based counterparts,which can be attributed to the difficulties in achieving favorable morphology.Herein,two asymmetric porphyrin-based donors named DAPor-DPP and DDPor-DPP were synthesized,presenting stronger intermolecular interaction and closer molecular stacking compared to the symmetric ZnP-TEH.The DAPor-DPP:6TIC blend afforded a favorablemorphologywith nanoscale phase separation and more ordered molecular packing,thus achievingmore efficient charge transportation and suppressed charge recombination.Consequently,the DAPor-DPP:6TIC-based device exhibited superior photovoltaic parameters,yielding a champion PCE of 16.62%higher than that of the DDPor-DPP-based device(14.96%).To our knowledge,16.62%can be ranked as one of the highest PCE values among the binary ASM OSC filed.Thiswork provides a prospective approach to address the challenge ofASM OSCs in improving film morphology and further achieving high efficiency via side-chain symmetry-breaking strategy,exhibiting great potential in constructing efficient ASM OSCs.

Trialkylsilyl-thiophene-conjugated acceptor for efficient organic solar cells compatible with spin-coating and blade-coating technologies

Sidechain engineering as an efficient and convenient strategy has been widely used to optimize molecular structure of photovoltaic materials for boosting power conversion efficiency(PCE)of organic solar cells(OSCs).Herein,a new Y-series acceptor named Y-Th Si with trialkylsilyl-substituted thiophene as conjugated sidechain is developed.Compared with its parental Y6 with multiple intermolecular interactions,Y-Th Si has a unitary molecular packing due to the additional steric hindrance from twodimensional(2D)-conjugated trialkylsilyl-thiophene.Therefore,Y-Th Si shows an obviously blue-shifted absorption with an onset of~850 nm but significantly up-shifted lowest unoccupied molecular orbital energy level.For the PM6:Y-Th Si pair,the spin-coating OSCs achieve a decent PCE of 14.56%with an impressively high photovoltage(V_(OC))of 0.936 V.Inspired by its high V_(OC)and narrow absorption,Y-Th Si is introduced into near-infrared absorbing binary PM6:BTP-eC9 host to construct ternary OSCs.Thanks to the complementary absorption,optimized morphology,and minimized energy loss properties,the PM6:BTP-e C9:Y-Th Si-based OSCs offer a higher PCE of 18.34%.Moreover,our developed strategy can overcome the commonly existed PCE drop when the blade-coating towards large-scale printing is used instead.Therefore,a comparable PCE of 18.34%is achieved,which is one of the best values for the blade-coating OSCs so far.

Exploiting the donor-acceptor-additive interaction’s morphological effect on the performance of organic solar cells

Organic solar cells(OSCs)have demonstrated over 19%power conversion efficiency(PCE)with the help of material innovation and device optimization.Co-working with newly designed materials,traditional solvent additives,1-chloronaphthalene(CN),and 1,8-diodooctane(DIO)are still powerful in morphology modulation towards satisfying efficiencies.Here,we chose recently reported high-performance polymer donors(PM6&D18-Fu)and small molecular acceptors(Y6&L8-BO)as active layer materials and processed them by different conditions(CN or DIO or none).Based on corresponding 12 groups of device results,and their film morphology characterizations(both ex-situ and in-situ ones),the property-performance relationships are revealed case by case.It is thereby supposed to be taken as a successful attempt to demonstrate the importance and complexity of donor-acceptoradditive interaction,since the device performance and physics analyses are also tightly combined with morphology variation.Furthermore,ternary blend construction for PCE improvement provides an approaching 19%level and showcases the potential of understanding-guided-optimization(UGO)in the future of OSCs.

Breaking 12% efficiency in flexible organic solar cells by using a composite electrode

The performance of flexible organic solar cells(OSCs)significantly relies on the quality of transparent flexible electrode.Here,we used silver nanowires(AgNWs)with various weight ratios to dope high-conductive poly(3,4-ethylenedioxythiophene):polystyrene sulfonate(PH1000)to optimize the optical and electronic properties of PH1000 film.A high-quality flexible composite electrode PET/Ag-mesh/PH1000:AgNWs-20 with smooth surface,a low sheet resistance of 6Ω/sq and a high transmittance of 86%at 550-nm wavelength was obtained by doping 20 wt%AgNWs to PH1000(PH1000:AgNWs-20).The flexible OSCs based on the PET/Ag-mesh/PH1000:AgNWs-20 electrode delivered a power conversion efficiency(PCE)of12.07%with an open circuit voltage(Voc)of 0.826 V,a short-circuit current density(Jsc)of 20.90 m A/cm2and a fill factor(FF)of69.87%,which is the highest reported PCE for the flexible indium-tin oxide(ITO)-free OSCs.This work demonstrated that the flexible composite electrodes of PET/Ag-mesh/PH1000:AgNWs are promising alternatives for the conventional PET/ITO electrode,and open a new avenue for developing high-performance flexible transparent electrode for optoelectronic devices.

Over 16.7% efficiency of ternary organic photovoltaics by employing extra PC71BM as morphology regulator

Ternary organic photovoltaics(OPVs)are fabricated with PBDB-T-2 Cl:Y6(1:1.2,wt/wt)as the host system and extra PC71BM as the third component.The PBDB-T-2 Cl:Y6 based binary OPVs exhibit a power conversion efficiency(PCE)of 15.49%with a short circuit current(JSC)of 24.98 mA cm^-2,an open circuit voltage(VOC)of 0.868 V and a fill factor(FF)of 71.42%.A 16.71%PCE is obtained in the optimized ternary OPVs with PBDB-T-2 Cl:Y6:PC71BM(1:1.2:0.2,wt/wt)active layer,resulting from the synchronously improved JSC of 25.44 mA cm^-2,FF of 75.66%and the constant VOCof 0.868 V.The incorporated PC71BM may prefer to mix with Y6 to finely adjust phase separation,domain size and molecular arrangement in ternary active layers,which can be confirmed from the characterization on morphology,2 D grazing incidence small and wide-angle X-ray scattering,as well as Raman mapping.In addition,PC71BM may prefer to mix with Y6 to form efficient electron transport channels,which should be conducive to charge transport and collection in the optimized ternary OPVs.This work provides more insight into the underlying reasons of the third component on performance improvement of ternary OPVs,indicating ternary strategy should be an efficient method to optimize active layers for synchronously improving photon harvesting,exciton dissociation and charge transport,while keeping the simple cell fabrication technology.

Tandem organic solar cells with efficiency over 19% via the careful subcell design and optimization

The series-connected tandem device strategy is an effective approach to promote the efficiency of organic solar cells(OSCs) with broadened absorption range and alleviated thermalization and transmission loss.In this article,two nonfullerene acceptors,FB rThCl and BTP-4Se,with complementary absorptions covering the range from 300 to 1,000 nm were designed and synthesized for the front and rear cell,respectively.The front cell based on D18:FBr-ThCl exhibited a Voc of 1.053 V with high external quantum efficiency(EQE) response values ranging from 300 to 740 nm.The rear cell with a ternary active layer PM6:BTP-4 Se:F-2F was optimized and afforded the Voc of 0.840 V and Jsc of 26.88 mA cm^(-2).Subsequently,the tandem device was constructed with a fully solution-processed interconnected layer of ZnO/PEDOT:PS S/PMA,and demonstrated a power conversion efficiency(PCE) of 19.55% with a Voc of 1.880 V,a Jsc of 13.25 mA cm^(-2) and an FF of 78.47%.

Synergistic effect of solvent and solid additives on morphology optimization for high-performance organic solar cells

Controlling the photoactive layer morphology towards nanoscale bi-continuous donor/acceptor interpenetrating networks is a key issue to build high-performance organic solar cells(OSCs).Due to the distinct properties between donor and acceptor materials,casting an active layer from a single solvent solution usually results in either insufficient or excessive phase separation that reduces the device performance.In comparison to the fullerene acceptors with closed-cage structures,the currently dominant non-fullerene acceptors possess the similar anisotropicπ-πinteractions with p-type organic semiconductor donors,giving rise to the complexity of the morphology regulation.Herein,we employ 4,4′-dimethoxyoctafluorobiphenyl(OFP)with strong crystallinity as a volatile solid additive to optimize the active layer morphology of OSCs.The synergistic effect of 1-chloronaphthalene(CN)and OFP as dual additives shows supreme capability on optimizing the morphology over the conventional additive of CN,which is in favor of improving charge transport and suppressing charge recombination for higher fill factors in various systems.In particular,the PTQ10:m-BTP-C6 Ph-based device processed by the additive showed a remarkable powerconversion efficiency(PCE)of 17.74%,whereas the control device processed by CN additive yielded a relatively lower PCE of16.45%.

Non-Fully Conjugated Photovoltaic Materials with Y-Series Acceptor Backbone for High-Performance Organic Solar Cells

In the last few years,organic solar cells(OSCs)have made significant progress in photovoltaic performance,mainly due to the innovative development of active layer materials,especially Y-series and related derivatives as acceptors which have become the key factor that boosts the power conversion efficiency.Recently,to achieve high-performance OSCs,an emerging molecular design strategy of applying flexible alkyl units as linkers to construct non-fully conjugated acceptors has been developed and addressed great attention.This review highlights the non-fully conjugated photovoltaic materials with Y-series backbone that enable high-performance OSCs.Impressive OSCs have been achieved by some representative non-fully conjugated material systems.The related molecular design strategies are discussed in detail.Finally,a brief summary and future prospect are provided in advancing the non-fully conjugated photovoltaic materials with Y-series backbone towards the brighter future.

Altering alkyl-chains branching positions for boosting the performance of small-molecule acceptors for highly efficient nonfullerene organic solar cells

The emergence of the latest generation of small-molecule acceptor(SMA)materials,with Y6 as a typical example,accounts for the surge in device performance for organic solar cells(OSCs).This study proposes two new acceptors named Y6-C2 and Y6-C3,from judicious alteration of alkyl-chains branching positions away from the Y6 backbone.Compared to the Y6,the Y6-C2 exhibits similar optical and electrochemical properties,but better molecular packing and enhanced crystallinity.In contrast,the Y6-C3 shows a significant blue-shift absorption in the solid state relative to the Y6 and Y6-C2.The as-cast PM6:Y6-C2-based OSC yields a higher power conversion efficiency(PCE)of 15.89%than those based on the Y6(15.24%)and Y6-C3(13.76%),representing the highest known value for as-cast nonfullerene OSCs.Prominently,the Y6-C2 displays a good compatibility with the PC71BM.Therefore,a ternary OSC device based on PM6:Y6-C2:PC71BM(1.0:1.0:0.2)was produced,and it exhibits an outstanding PCE of 17.06%and an impressive fill factor(FF)of 0.772.Our results improve understanding of the structureproperty relationship for state-of-the-art SMAs and demonstrate that modulating the structure of SMAs via fine-tuning of alkylchains branching positions is an effective method to enhance their performance.

A major step toward efficient and stable single-material organic solar cells

Organic photovoltaics (OPV) can potentially combine low cost, lightness, flexibility and low environmental impact. In less than two decades, the power conversion efficiency(PCE) of OPV cells has increased from 1 to more than 15%thanks to parallel efforts in material design and device technology.

Stable Radical TEMPO Terminated Perylene Bisimide(PBI) Based Small Molecule as Cathode Interlayer for Efficient Organic Solar Cells

By combining stable radical tetramethylpiperidine nitrogen oxide(TEMPO)as end groups and perylene bisimide(PBI)as the core,a small molecular cathode interlayer(CIL)(PBI-TEMPO)was synthesized.Detailed physical-chemical characterizations indicate that PBI-TEMPO can form smooth film,owns low unoccupied molecular orbital(LUMO)level of−3.67 eV and can reduce the work function of silver electrode.When using PBI-TEMPO as CIL in non-fullerene organic solar cells(OSCs),the PM6:BTP-4Cl based OSCs delivered high power conversion efficiencies(PCEs)up to 17.37%,higher than those using commercial PDINO CIL with PCEs of 16.95%.Further device characterizations indicate that PBI-TEMPO can facilitate more efficient exciton dissociation and reduce charge recombination,resulting in enhanced current density and fill factor.Moreover,PBI-TEMPO displays higher thermal stability than PDINO in solution.When PBI-TEMPO and PDINO solution were heated at 150℃ for 2 h and then were used as CIL in solar cells,PBI-TEMPO-based OSCs provided a PCE of 15%,while PDINO-based OSCs only showed a PCE of 10%.These results demonstrate that incorporating TEMPO into conjugated materials is a useful strategy to create new organic semiconductors for application in OSCs.

Organic functional materials based buffer layers for efficient perovskite solar cells

In this review, we highlight the recent development of organic π-functional materials as buffer layers in constructing efficient perovskite solar cells（PVSCs）. By following a brief introduction on the PVSC development, device architecture and material design features, we exemplified the exciting progresses made in field by exploiting organic π-functional materials based hole and electron transport layers（HTLs and ETLs） to enable high-performance PVSCs.

Manipulating Nanowires in Interconnecting Layer for Efficient Tandem Organic Photovoltaics

Owing to the function of manipulating light absorption distribution,tandem organic solar cells containing multiple sub-cells exhibit high power conversion efficiencies.However,there is a substantial challenge in precisely controlling the inter-subcells carrier migration which determines the balance of charge transport across the entire device.The conductivity of"nanowires"-like conducting channel in interconnecting layer between sub-cells should be improved which calls for fine engineering on the morphology of polyelectrolyte in interconnecting layer.Here,we develop a simple method to effectively manipulating the domains of conductive components in commercially available polyelectrolyte PEDOT:PSs.The use of poor solvent could effectively modify the configuration of polystyrene sulfonic acid and thus the space for conductive components.Based on our strategy,the insulated shells wrapping conductive domains are thinned and the efficiencies of tandem organic solar cells are improved.We believe our method might provide guidance for the manufacture of tandem organic solar cells.

Recent progress in organic solar cells(PartⅠmaterial science)

During past several years,the photovoltaic performances of organic solar cells(OSCs)have achieved rapid progress with power conversion efficiencies(PCEs)over 18%,demonstrating a great practical application prospect.The development of material science including conjugated polymer donors,oligomer-like organic molecule donors,fused and nonfused ring acceptors,polymer acceptors,single-component organic solar cells and water/alcohol soluble interface materials are the key research topics in OSC field.Herein,the recent progress of these aspects is systematically summarized.Meanwhile,the current problems and future development are also discussed.

Tuning Aggregation Behavior of Polymer Donor via Molecular-Weight Control for Achieving 17.1%Efficiency Inverted Polymer Solar Cells

Main observation and conclusion Recently,the polymer solar cells(PSCs)based on the PM6 and small molecular acceptor(SMA)Y6 have attracted considerable attention in this community for their outstanding photovoltaic performance.