Ternary strategy: An analogue as third component reduces the energy loss and improves the efficiency of polymer solar cells

Ternary strategy is a convenient and effective method to boost the performance of polymer solar cells(PSCs).Utilizing a ternary strategy to trade-off between the energy loss and the efficiency of devices however requires further exploration.Here,through the hydroxyl(-OH)and acetoxy(-OCOMe)substitution atβ-position of the IC terminal group,we developed two new synthetic acceptors,BTIC-OH-βand BTICOCOMe-β,which were designed to confine the morphology aggregation.Introduction of an analogue as the third component provides a simple but efficient way to further balance the short current density(Jsc)and open-circuit voltage(Voc),leading to a champion efficiency based on PBDB-T:PBDB-TF:BTIC-OCOMe-β,effectively as high as 12.45%.The results were examined mainly in terms of the morphology characterization,electroluminescence external quantum efficiency(EQEEL),steady-state photoluminescence(PL)and transient technology.It suggested fine-tuning of the morphology by ratio modulation,reduction of the energy loss,construction of a promising pathway for charge transfer in the ternary system and enhancing the carrier extraction.In this way,a ternary strategy with an analogue donor could provide more routes to higher-quality solar cells.

Enhancing photostability and power conversion efficiency of organic solar cells by a “sunscreen” ternary strategy

The field has witnessed the rapid growth in the power conversion efficiency(PCE)of organic solar cells(OSCs)over the past decade,reaching the threshold for practical commercialization.However,a major issue remains that OSC lifetimes are seriously limited by the ultraviolet(UV)-induced photodegradation.Here,inspired by the superior photostability of car paint under sunlight and ambient air,a“sunscreen”molecule,2-(2-hydroxy-5-tert-octylphenyl)benzotriazole(UV329),is used to construct the PM6:Y6 ternary device.The addition of UV329 mainly enhances the ordered stacking of PM6 and increases the light utilization of blend films with the improved crystallization and appropriate phase separation.Accordingly,the ternary device exhibits stronger light response and obviously higher and more balanced carrier mobilities,contributing to higher short-circuit current density,fill factor and PCE.Similar PCE boost is also verified in PM6:BTP-e C9 and PM6:L8-BO systems.The photodegradation of PM6 dominates the photo-degradation process of PM6:Y6 systems,while the UV329 can effectively suppress such degradation,and thus the ternary device can retain nearly 90%of the initial PCE under continuous illumination for 120 min.Moreover,ternary devices also preserve better thermal stability and shelf-life with the enhanced PCE.This work provides a simple yet effective strategy for simultaneously improving PCE and photostability of OSCs.

Suppressing trap states and energy loss by optimizing vertical phase distribution through ternary strategy in organic solar cells

Suppressing the trap-state density and the energy loss via ternary strategy was demonstrated.Favorable vertical phase distribution with donors(acceptors)accumulated(depleted)at the interface of active layer and charge extraction layer can be obtained by introducing appropriate amount of polymer acceptor N2200 into the systems of PBDB-T:IT-M and PBDB-TF:Y6.In addition,N2200 is gradiently distributed in the vertical direction in the ternary blend film.Various measurements were carried out to study the effects of N2200 on the binary systems.It was found that the optimized morphology especially in vertical direction can significantly decrease the trap state density of the binary blend films,which is beneficial for the charge transport and collection.All these features enable an obvious decrease in charge recombination in both PBDB-T:IT-M and PBDB-TF:Y6 based organic solar cells(OSCs),and power conversion efficiencies(PCEs)of 12.5%and 16.42%were obtained for the ternary OSCs,respectively.This work indicates that it is an effective method to suppress the trap state density and thus improve the device performance through ternary strategy.

Realizing high-performance organic solar cells through precise control of HOMO driving force based on ternary alloy strategy

A good deal of studies have proven that effective exciton dissociation and fast hole transport can operate efficiently in non-fullerene organic photovoltaics(OPVs)despite nearly zero driving force.Even so,whether such a phenomenon is universal and how small the driving force can realize the best photovoltaic performance still require a thorough understanding.Herein,despite the zero driving force based on PM6:F8IC system,a maximum short-circuit current(J_(sc))of 23.0 mA/cm^(2) and high power conversion efficiency(PCE)of 12.2%can still be achieved.Due to the continuously adjustable energy levels can be realized in organic semiconducting alloys including F8IC:IT-4F and F8IC:Y6,the suitable third components can play the role of energy level regulator.Therefore,the HOMO energy level offset(DEHOMO(D A))from zero to 0.07 and 0.06 eV is accomplished in the optimized IT-4F and Y6 ternary devices.Consequently,both ternary devices achieved substantially increased PCE of 13.8%and Jsc of 24.4 and 25.2 mA/cm^(2),respectively.Besides,pseudo-planar heterojunction(PPHJ)devices based on alloyed acceptors through sequential spin-coating method further improve the photovoltaic performance.Our work puts forward the concept of energy level regulator and prove that the ternary alloy strategy has unique advantages and huge research potential in continuously adjusting the driving force.

19.3% Efficiency ternary organic solar cells enabled by the alkyl side-chain effect of guest non-fullerene acceptors

The effect of side-chain engineering of conjugated molecules on the morphology and device performance in binary organic solar cells has been widely investigated. However, this relationship has hardly been studied in the guest components of ternary organic solar cells. In this study, a family of non-fullerene guest acceptors, namely XY-3, XY-5 and XY-7, with hydrogen substituent,straight and branched alkyl chains on the bithiophene units, respectively, were designed and synthesized to understand their effects on aggregation properties and device performance. The straight and branched alkyl chains on the bithiophene units result in sightly blue-shifted absorption compared to the hydrogen substituent and the XY-7 demonstrates the most appropriate phase separation scale and the most balanced charge transport. Consequently, the OSCs based on D18:e C9:XY-7 achieve a high shortcircuit current density(JSC) and fill factor(FF), while maintaining the enhancement of the open-circuit voltage(VOC) achieving an efficiency of 19.32%, exceeding those of D18:e C9, D18:e C9:XY-3, D18:e C9:XY-5(PCE:18.28%, 19.04%, 18.75%, respectively). These results highlight that the side-chain engineering of Y series non-fullerene acceptors as the guest acceptors has great potential in optimizing morphology properties and promoting photovoltaic performance.

Reducing the voltage loss of Y-series acceptor based organic solar cells via ternary/quaternary strategies

In recent years, with the emergence of non-fullerene fused-ring acceptors, power conversion efficiencies (PCEs) of organic solar cells (OSCs) have exceeded 19%.However, compared to inorganic or perovskite photovoltaic cells, a higher voltage loss has become one of the key factors limiting further improvement in the PCEs of OSCs.The ternary/quaternary strategy has been identified as a feasible and effective way to obtain high-efficiency OSCs.In this review, a brief outline is given of the key roles that guest materials played in reducing voltage losses in solar cell devices and a brief look at the future material design and the design of ternary/quaternary systems.

14.46% Efficiency small molecule organic photovoltaics enabled by the well trade-off between phase separation and photon harvesting

Small molecule organic photovoltaics(SMPVs) were prepared by utilizing liquid crystalline donor material BTR-Cl and two similar optical bandgap non-fullerene acceptor materials BTP-BO-4 F and Y6.The BTPBO-4 F and Y6 have the similar optical bandgap and different absorption coefficients.The corresponding binary SMPVs exhibit different short circuit current density(/sc)(20.38 vs.23.24 mA cm^(-2)),and fill factor(FF)(70.77% vs.67.21%).A 14.46% power conversion efficiency(PCE) is acquired in ternary SMPVs with 30 wt% Y6,companied with a JSC of 24.17 mA cm^(-2) a FF of 68.78% and an open circuit voltage(Voc) of 0.87 V.The improvement on PCE of ternary SMPVs should originate from the well trade-off between phase separation and photon harvesting of ternary active layers by incorporating 30 wt% Y6 in acceptors.This work may deliver insight onto the improved performance of SMPVs by superposing the superiorities of binary SMPVs with similar optical bandgap acceptors into one ternary cell.

Synergetic Alkoxy Side-Chain and Chlorine-Contained End Group Strategy toward High Performance Ultra-Narrow Bandgap Small Molecule Acceptors

Ultra-narrow bandgap(ultra-NBG)small molecule acceptors(SMAs)show great potential in organic solar cells(OSCs)due to the extended near-infrared(NIR)absorption.In this work,a synergetic alkoxy side-chain and chlorine-contained end group strategy is employed to achieve A-DA'D-A type ultra-NBG SMAs by introducing alkoxy chains with oxygen atom at the second position into the thiopheneβposition as well as replacing the F atoms with Cl atoms in the end group.As a result,the heptacyclic BZO-4F shows a redshifted absorption onset(960 nm)compared with Y11(932 nm)without oxygen atoms in the side chains.Then,the fluorinated end groups are substituted with the chlorinated ones to synthesize BZO-4Cl.The absorption onset of BZO-4Cl is further redshifted to 990 nm,corresponding to an optical ultra-NBG of 1.25 eV.When blending with the polymer donor PBDB-T,the binary devices based on PBDB-T:BZO-4F and PBDB-T:BZO-4Cl deliver power conversion efficiencies(PCEs)over 12%.Furthermore,ternary devices with the addition of BZ4F-O-1 into PBDB-T:BZO-4Cl system achieve the optimal PCE of 15.51%.This work proposes a synergetic alkoxy side-chain and chlorine-contained end group strategy to achieve A-DA'D-A type ultra-NBG SMAs,which is important for future molecular design.

Manipulating Film Formation Kinetics Enables Organic Photovoltaic Cells with 19.5%Efficiency

Organic photovoltaic(OPV)cells have demonstrated remarkable performance in small,spin-coated areas.Nevertheless significant challenges persist in the form of large efficiency losses due to the fact that the ideal morphology cannot be preserved in the transition of small-area cells to large-scale panels.Herein,the ternary strategy of incorporating the third component FTCC-Br into the active layer of PB2:BTP-eC9 is employed to improve absorption response,optimize morphology,and reduce charge recombination,leading to a power conversion efficiency(PCE)of 19.5%(certified as 19.1%by the National Institute of Metrology,China).Moreover,the addition of FTCC-Br can control the aggregation kinetics of the active layer during the film formation process,transferring the optimal morphology to the blade-coated large-area films.Based on the highly efficient ternary bulk heterojunction,the 50 cm^(2) OPVmodules exhibited a PCE of 15.2%with respect to the active area.Importantly,the ternary OPV cells retain 80%of its initial PCE after 4000 h under continuous illumination.Our work demonstrates that the addition of a third component has the potential to improve the efficiency and stability of large-area organic solar cells.

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.

Inner alkyl chain modulation of small molecular acceptors enables molecular packing optimization and efficient organic solar cells

With the generation of Y6,organic solar cells have reached remarkable achievement of over 19%efficiency.Alkyl chain is of importance to modulate intermolecular stacking and possibly enhance optoelectronic properties of small molecule acceptors(SMAs).Three alkyl chains of 2-ethylhexyl,2-butylocyl and 3-ethylheptyl were selected to obtain G6-EH,G6-BO and G6-EHep molecules,respectively.Compared to G6-EH and G6-BO,G6-EHep was found inducing unfavourable large domain size.Furthermore,we discover that 2-butyloctyl effectively inhibits monomolecular and bimolecular recombination,improves molecular packing,generates more balanced carrier mobility and enhances exciton dissociation.The SMA with 2-butyloctyl alkyl chains(G6-BO)shows the best electrical and morphological characteristics,achieving a higher power conversion efficiency(PCE)of 17.06%,with an open circuit voltage of 0.912 V,a short-circuit current of 24.22 m A cm-2and a fill factor of 77.25%.Finally,using the ternary strategy by incorporating the G6-BO acceptor into PM6:BTP-e C9,we achieved a higher PCE of18.13%with enhanced electron transport.

Controllable Exciton Diffusion Length and Ultrafast Charge Generation in Ternary Organic Solar Cells

Charge generation,a critical process in the operation of organic solar cell(OSC),requires thorough investigation in an ultrafast perspective.This work demonstrates that the utilization of alloy model for the non-fullerene acceptor(NFA)component can regulate the crystallization properties of active layer films,which in turn affects exciton diffusion and hole transfer(HT),ultimately influencing the charge generation process.By incorporating BTP-eC7 as a third component,without expanding absorption range or changing molecular energy levels but regulating the ultrafast exciton diffusion and HT processes,the power conversion efficiency(PCE)of the optimized PM6:BTP-eC9:BTP-eC7 based ternary OSC is improved from 17.30%to 17.83%,primarily due to the enhancement of short-circuit current density(JSC).Additionally,the introduction of BTP-eC7 also reduces the trap state density in the photoactive layer which helps to reduce the loss of JSC.This study introduces a novel approach for employing ternary alloy models by incorporating dual acceptors with similar structures,and elucidates the underlying mechanism of charge generation and JSC in ternary OSCs.

Chlorinated Thiazole-Based Low-Cost Polymer Donors for High Efficiency Binary and Ternary Organic Solar Cells

In this work,novel D-A alternating polymers(PJ-1,PJ-2,and PJ-3)with chlorinated benzodithiophene and chlorinated thiazole units were synthesized via gradual chlorination.These polymers could be obtained readily through a few concise synthesis steps.Among them,PJ-1 displayed desirable properties including energy levels,crystallinity,and charge transport capabilities.The binary and ternary organic solar cells(OSCs)fabricated based on PJ-1 displayed significant power conversion efficiency(PCE)of 15.02%and 19.12%,respectively,placing them among the highest reported for ternary OSCs.Notably,the PJ1-based devices also showcased one of the highest figure-of-merit values,indicating their promising potential for future applications.This study offers valuable insights and supports the development of costeffective and high-performance polymer donors for the generation of OSCs.