Dithienocarbazole- and benzothiadiazole-based donor-acceptor conjugated polymers for bulk heterojunction polymer solar cells

Donor-acceptor(D-A)-conjugated polymers P(BT-C1)and P(BT-C2),with dithieno[2,3-b;7,6-b]carbazole(C1)or dithieno[3,2-b;6,7-b]carbazole(C2)as D-unit and benzothiadiazole(BT)as A-unit,were synthesized.The optical bandgaps of the polymers are similar(1.84 and 1.88 e V,respectively).The structures of donor units noticeably influence the energy levels and backbone curvature of the polymers.P(BT-C1)shows a large backbone curvature;its highest occupied molecular orbital(HOMO)energy level is 5.18 e V,whereas P(BT-C2)displays a pseudo-straight backbone and has a HOMO energy level of 5.37 e V.The hole mobilities of the polymers without thermal annealing are 1.9×10 3 and 2.7×10 3 cm2 V 1 s 1 for P(BT-C1)and P(BT-C2),respectively,as measured by organic thin-film transistors(OTFTs).Polymer solar cells using P(BT-C1)and P(BT-C2)as the donor and phenyl-C71-butyric acid methyl ester(PC71BM)as the acceptor were fabricated.Power conversion efficiencies(PCEs)of 4.9%and 5.0%were achieved for P(BT-C1)and P(BT-C2),respectively.The devices based on P(BT-C2)exhibited a higher Voc due to the deeper HOMO level of the polymer,which led to a slightly higher PCE.     

Rylene diimide and dithienocyanovinylene copolymers for polymer solar cells

Two polymers containing(E)-2,3-bis(thiophen-2-yl)acrylonitrile(CNTVT) as a donor unit, perylene diimide(PDI) or naphthalene diimide(NDI) as an acceptor unit, are synthesized by the Stille coupling copolymerization, and used as the electron acceptors in the solution-processed organic solar cells(OSCs). Both polymers exhibit broad absorption in the region of 300–850 nm. The LUMO energy levels of the resulted polymers are ca. –3.93 eV and the HOMO energy levels are –5.97 and –5.83 eV. In the binary blend OSCs with PTB7-Th as a donor, PDI polymer yields the power conversion efficiency(PCE) of up to 1.74%, while NDI polymer yields PCE of up to 3.80%.     

Side-chain engineering of high-efficiency conjugated polymer photovoltaic materials

In recent years,conjugated polymers have attracted great attention in the application as photovoltaic donor materials in polymer solar cells(PSCs).Broad absorption,lower-energy bandgap,higher hole mobility,relatively lower HOMO energy levels,and higher solubility are important for the conjugated polymer donor materials to achieve high photovoltaic performance.Side-chain engineering plays a very important role in optimizing the physicochemical properties of the conjugated polymers.In this article,we review recent progress on the side-chain engineering of conjugated polymer donor materials,including the optimization of flexible side-chains for balancing solubility and intermolecular packing(aggregation),electron-withdrawing substituents for lowering HOMO energy levels,and two-dimension(2D)-conjugated polymers with conjugated side-chains for broadening absorption and enhancing hole mobility.After the molecular structural optimization by side-chain engineering,the2D-conjugated polymers based on benzodithiophene units demonstrated the best photovoltaic performance,with powerconversion efficiency higher than 9%.     

Synthesis of two-dimensional π-conjugated polymers pendent with benzothiadiazole and naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole moieties for polymer solar cells

Four new 2D donor–acceptor conjugated polymers were designed and synthesized.These new polymers comprised fluorenealt-triphenylamine or carbazole-alt-triphenylamine as the backbones,and pendants with 2,1,3-benzothiadiazole(BT)or naphtho[1,2-c:5,6-c]bis[1,2,5]thiadiazole(NT)in a triphenylamine unit as the side groups.By changing the acceptor BT for a stronger electron-withdrawing unit of NT moiety in the side chain,the energy levels,absorption spectra,band gaps,and charge-transport abilities of the resultant polymers could be effectively tuned.Bulk heterojunction solar cells with these polymers as the electron donors and(6,6)-phenyl-C71-butyric acid methyl ester as the electron acceptor exhibited high open-circuit voltage(more than 0.8 e V).The power conversion efficiency can be improved from 1.37%to 3.52%by replacing the BT with an NT moiety,which indicates that introducing NT as the side-chain building block can be an effective strategy to construct efficient 2D conjugated polymers for PSCs.     

Effect of furan π-bridge on the photovoltaic performance of D-A copolymers based on bi(alkylthio-thienyl)benzodithiophene and fluorobenzotriazole

The medium band gap donor-acceptor(D-A) copolymer J61 based on bi(alkylthio-thienyl)benzodithiophene as donor unit and fluorobenzotriazole as acceptor unit and thiophene as π-bridge has demonstrated excellent photovoltaic performance as donor material in nonfullerene polymer solar cells(PSCs) with narrow bandgap n-type organic semiconductor ITIC as acceptor.For studying the effect of π-bridges on the photovoltaic performance of the D-A copolymers,here we synthesized a new D-A copolymer J61-F based on the same donor and acceptor units as J61 but with furan π-bridges instead of thiophene.J61-F possesses a deeper the highest occupied molecular orbital(HOMO) level at-5.45 eV in comparison with that(-5.32 eV) of J61.The non-fullerene PSCs based on J61-F:ITIC exhibited a maximum power conversion efficiency(PCE) of 8.24%with a higher open-circuit voltage(V_(oc)) of 0.95 V,which is benefitted from the lower-lying HOMO energy level of J61-F donor material.The results indicate that main chain engineering by changing π-bridges is another effective way to tune the electronic energy levels of the conjugated D-A copolymers for the application as donor materials in non-fullerene PSCs.     

Synergistic effect of fluorination on both donor and acceptor materials for high performance non-fullerene polymer solar cells with 13.5% efficiency

A high performance polymer solar cells(PSCs) based on polymer donor PM6 containing fluorinated thienyl benzodithiophene unit and n-type organic semiconductor acceptor IT-4 F containing fluorinated end-groups were developed. In addition to complementary absorption spectra(300–830 nm) with IT-4 F, the PM6 also has a deep HOMO(the highest occupied molecular) level(-5.50 e V), which will lower the open-circuit voltage(V_(oc)) sacrifice and reduce the E_(loss) of the IT-4 F-based PSCs. Moreover, the strong crystallinity of PM6 is beneficial to form favorable blend morphology and hence to suppress recombination. As a result, in comparison with the PSCs based on a non-fluorinated D/A pair of PBDB-T:ITIC with a medium PCE of 11.2%, the PM6:IT-4 Fbased PSCs yielded an impressive PCE of 13.5% due to the synergistic effect of fluorination on both donor and acceptor, which is among the highest values recorded in the literatures for PSCs to date. Furthermore, a PCE of 12.2% was remained with the active layer thickness of up to 285 nm and a high PCE of 11.4% was also obtained with a large device area of 1 cm~2. In addition, the devices also showed good storage, thermal and illumination stabilities with respect to the efficiency. These results indicate that fluorination is an effective strategy to improve the photovoltaic performance of materials, as well as the both fluorinated donor and acceptor pair-PM6:IT-4 F is an ideal candidate for the large scale roll-to-roll production of efficient PSCs in the future.     

Metallated conjugation in small-sized-molecular donors for solution-processed organic solar cells

Four metallated conjugated oligothiophenes,S-1,S-2,S-3 and S-4,with platinum(II)aryleneethynylenes as the electron-rich building block were synthesized to investigate their physicochemical and photovoltaic properties.These small molecules possess fairly low-lying HOMO energy levels which match with the LUMO energy level of the electron acceptor PC70BM([6,6]-phenyl-C71-butyric acid methyl ester).Using the simple process of spin-coating solution fabrication technique,S-1:PC70BM(1:4,w/w)based organic solar cells exhibiting a high Voc of 0.913 V,with a PCE value of 0.88%were developed.In contrast,the OSC device based on S-2:PC70BM(3:7,w/w)displayed a higher PCE of 1.59%with a higher Jsc value of 5.89m A cm–2.The device based on S-4:PC70BM(1:4,w/w)exhibited a PCE value of 1.56%,with a Voc of 0.917 V.     

Highly efficient random terpolymers for photovoltaic applications with enhanced absorption and molecular aggregation

A series of copolymers, based on benzo[1,2-b:4,5-b′]dithiophene(BDT) as the electron donor and 2,1,3-benzothiadiazole(BT)/diketopyrrolo[3,4-c]pyrrole(DPP) as the electron acceptors, were synthesized for highly efficient polymer solar cells. By changing the BT/DPP ratio in the conjugated backbone, the absorption, energy levels, molecular aggregation and carrier mobility could be finely tuned. With increased DPP content, the absorption range was extended to the longer wavelength region with narrower bandgaps. The highest occupied molecular orbital(HOMO) levels were also raised up and the molecular aggregation was enhanced. The balance of these factors would afford a remarkable device performance enhancement. Polymer P3 with BT:DPP = 0.7:0.3(molar ratio) exhibited the highest power conversion efficiency(PCE) of 9.01%, with open circuit voltage(V_(oc)) = 0.73 V, short current density(J_(sc)) = 18.45 m A·cm~(-2), and fill factor(FF) = 66.9%. The PCE value was improved by 48.7% compared to P1 and by 117.6% compared to P7, respectively, indicating a great potential in photovoltaic application.     

Alkoxy substituted benzodithiophene-alt-fluorobenzotriazole copolymer as donor in non-fullerene polymer solar cells

A new benzodithiophene(BDT)-alt-fluorobenzotriazole(FBTA) D-A copolymer J40 was designed and synthesized by introducing 2-octyldodecyloxy side chains on its BDT units, for expanding the family of the BDT- alt-FBTA-based copolymers and investigating the side chain effect on the photovoltaic performance of the polymer in non-fullerene polymer solar cells(PSCs).J40 exhibits complementary absorption spectra and matched electronic energy levels with the n-type organic semiconductor(n-OS)(3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-sindaceno[1,2-b:5,6-b′]dithiophene)(ITIC) acceptor, and was used as polymer donor in the non-fullerene PSCs with ITIC as acceptor. The power conversion efficiency(PCE) of the PSCs based on J40:ITIC(1:1, w/w) with thermal annealing at 120 °C for 10 min reached 6.48% with a higher open-circuit voltage(Voc) of 0.89 V. The high Voc of the PSCs is benefitted from the lower-lying highest occupied molecular orbital(HOMO) energy level of J40. Although the photovoltaic performance of the polymer J40 with alkoxy side chain is lower than that of J60 and J61 with alkylthio-thienyl conjugated side chains, the PCE of6.48% for the J40-based device is still a relatively higher photovoltaic efficiency in the non-fullerene PSCs reported so far. The results indicate that the family of the BDT-alt-FBTA-based D-A copolymers are high performance polymer donor materials for non-fullerene PSCs and the side chain engineering plays an important role in the design of high performance polymer donors in the non-fullerene PSCs.     

Donor-Acceptor Oligomers and Polymers Composed of Benzothiadiazole and 3-Hexylthiophene： Effect of Chain Length and Regioregularity

A series of donor-acceptor oligomer OBTThn （n = 1- 7） and polymer PBTThl and PBTTh2 composed of al- ternative 2,1,3-benzothiadiazole and 3-hexylthiophene have been designed and synthesized for the purpose of in- vestigation on the effect of chain length and side-chain regioregularity on their basic properties and photovoltaic performance. In the OBTThn oligomers and PBTThl polymer, all the hexyl side chains on thienyl units orient to- ward the same direction. Upon elongation of the chain length, the intramolecular charge transfer （ICT） absorption band in solution gradually redshifts from 398 nm for OBTThl to 505 nm for OBTThT, then to 512 nm for PBTThl polymer. Meanwhile, the HOMO energy level increases from -5.45 eV （OBTTh0 to -5.08 eV （OBTThT） and -5.09 eV （PBTThl）, and the LUMO energy level decreases from -3.11 eV （OBTTh0 to -3.30 eV （OBTThT） and -3.33 eV （PBTThl）, thus giving a smaller and smaller energy bandgap for higher oligomers and polymers. Theo- retical calculation suggests straight line-like backbone geometry for this series of oligomers and polymer. On the other hand, polymer PBTTh2 possesses a different side-chain regioregularity, in which every two neighbor hexyl side chains are arranged in different orienting direction. It is theoretically suggested to have curved line-like back- bone geometry. In solution, it shows similar photophysical and electrochemical properties as PBTThl. However in film state, it displays a less redshift in the ICT band as refer to that in solution than PBTThl. In combination with [6,6]-phenyl-C61-butyric acid methyl ester （PC61BM）, these oligomers and polymers were used as donor material to fabricate organic bulk heterojunction solar cells. Again, chain length-dependent device photovoltaic performance was observed. The device based on OBTTh4 showed a power conversion efficiency of 0.16%, while it increased to 0.36% and 0.49% for the devices based on OBTTh6 and PBTThb respectively. However, the side-chain regio- regularity has less influence on the device photovoltaic output since the device based on PBTTh~ displayed an effi- ciency of 0.52%, comparable to that of PBTThl.     

Fine-tuning of polymer photovoltaic properties by the length of alkyl side chains

This paper reports the synthesis and characteristics of a series of alkyl-substituted planar polymers. The physical properties are carefully tuned to optimize their photovoltaic performance. Depending on the length of soluble alkyl side chains which modify the structural order and orientation substantially in polymer backbones, the device performance can be improved significantly. The tuning of HOMO energy levels optimized polymers’ spectral coverage of absorption and their hole mobility, as well as miscibility with fullerene; all these efforts enhanced polymer solar cell performances. The shortcircuit current, Jsc for polymer solar cells was increased by adjusting polymer chain packing ability. It was found that films with well distributed polymer/fullerene interpenetrating network exhibit improved solar cell conversion efficiency. Enhanced efficiency up to 5.8% has been demonstrated. The results provide important insights about the roles of flexile chains in structure-property relationship for the design of new polymers to be used in high efficient solar cells.     

8.0% Efficient all-polymer solar cells based on novel starburst polymer acceptors

The polymer N2200, with its π-conjugated backbone composed of alternating naphthalene diimide(NDI) and bithiophene(DT)units, has been widely used as an acceptor for all-polymer solar cells(all-PSCs) owing to its high electron mobility and suitable ionization potential and electron affinity. Here, we developed two naphthalene diimide derivatives by modifying the molecular geometry of N2200 through the incorporation of a truxene unit as the core and NDI-DTas the branches. These starburst polymers exhibited absorption spectra and molecular orbital energy levels that were comparable to N2200. These copolymers were paired with the wide-bandgap polymer donor PTz BI-O to fabricate all-polymer solar cells(all-PSCs), which displayed impressive power conversion efficiencies up to 8.00%. The improved photovoltaic performances of all-PSCs based on these newly developed starburst acceptors can be ascribed to the combination of increased charge carrier mobilities, reduced bimolecular recombination, and formation of more favorable film morphology. These findings demonstrate that the construction of starburst polymer acceptors is a feasible strategy for the fabrication of high-performance all-PSCs.     

Two-dimensional photovoltaic copolymers with spatial D-A-D structures: synthesis,characterization and hetero-atom effect

A series of two-dimensional(2D)conjugated copolymers with spatial D-A-D structures(PTNBTB,PTCBTB,and PTSBTB)consisting of hetero-atom-bridged dithiophene and phenylvinyl-substituted benzothiadiazole blocks in the main chain have been designed,synthesized,and characterized.The structure-property relationships of the resulting copolymers were systematically investigated.The effects of the bridging atoms(N,C,and Si)on their thermal,optical,electrochemical and chargetransporting properties were also studied.PTNBTB exhibits a smaller band gap with red-shifted absorption,whereas PTSBTB possesses deeper HOMO level and higher hole mobility than PTCBTB or PTSBTB.Bulk heterojunction(BHJ)solar cells were fabricated and characterized with the conventional configuration of ITO/PEDOT:PSS/copolymer:PC71BM(1:1)/Ca/Al.As expected,PTSBTB devices showed the highest PCE,up to 4.01%,which was due to the lower HOMO level,higher carrier mobility,and stronger optical response as well as the finer nanoscale phase separation of the pristine polymer and/or the corresponding blending active layer with PC71BM.The primary results offer useful insights in designing 2D copolymers with spatial D-A-D backbone and different hetero-atom bridged donor units to finely tune the absorptions,electronic energy levels,carrier mobilities and the photovoltaic properties.     

A universal tactic of using Lewis-base polymer-CNTs composites as additives for high performance cm~2-sized and flexible perovskite solar cells

Lewis-base polymers have been widely utilized as additives to act as a template for the perovskite nucleation/crystal growth and passivate the under-coordinated Pb2+ sites.However,it is uncovered in this work that the polymer on the perovskite grain boundaries would significantly hinder the charge transport due to its low conductivity,which brings about free carrier recombination and photocurrent losses.To circumvent this issue while fully exploiting the benefits of polymers in passivating the trap states in perovskite,we incorporate highly conductive multiwall carbon nanotubes(CNTs) with Lewis-base polymers as coadditives in the perovskite film.Functionalizing the CNTs with-COOH group enables a selective hole-extraction and charge transport from perovskite to the hole transporting materials(HTM).By studying the charge transporting and recombination dynamics,we revealed the individual role of the polymer and CNTs in passivating the trap states and facilitating the charge transport,respectively.As a result,the perovskite solar cells(PSCs) with polymer-CNTs composites exhibit an impressive PCE of 21.7% for a small-area device(0.16 cm2) and 20.7% for a large-area device(1.0 cm2).Moreover,due to the superior mechanical flexibility of both polymer and CNTs,the polymer-CNTs composites incorporation in the perovskite film encourages the fabrication of flexible PSCs(f-PSCs) with an impressive PCE of 18.3%,and a strong mechanical durability by retaining 80%of the initial PCE after 1,000 times bending.In addition,we proved that the selection criteria of the polymers can be extended to other long-chain Lewis-base polymers,which opens new possibilities in design and synthesis of inexpensive material for this tactic towards the fabrication of high performance large-area PSCs and f-PSCs.     

Low band-gap benzodithiophene-thienothiophenecopolymers: the effect of dual two-dimensional substitutions on optoelectronic properties

Two new conjugated copolymers,PBDT-T6-TTF and PBDT-T12-TTF,were derived from a novel 4-fluorobenzoyl thienothiophene(TTF).In addition,two types of benzodithiophene(BDT)units with 2,3-dihexylthienyl(T6)and 2,3-didodecylthienyl(T12)substituents,respectively,were successfully synthesized.The effect of the dual two-dimensional(2D)substitutions of the building blocks upon the optoelectronic properties of the polymers was investigated.Generally,the two polymers exhibited good solubility and broad absorption,showing similar optical band gaps of~1.53 e V.However,PBDT-T6-TTF with its shorter alkyl chain length possessed a larger extinction coefficient in thin solid film.The highest occupied molecular orbital(HOMO)level of PBDT-T6-TTF was located at–5.38 e V while that of PBDT-T12-TTF was at–5.51 e V.In space charge-limitedcurrent(SCLC)measurement,PBDT-T6-TTF and PBDT-T12-TTF displayed respective hole mobilities of 3.0×10–4 and1.6×10–5 cm2 V1 s1.In polymer solar cells,PBDT-T6-TTF and PBDT-T12-TTF showed respective power conversion efficiencies(PCEs)of 2.86%and 1.67%.When 1,8-diiodooctane(DIO)was used as the solvent additive,the PCE of PBDT-T6-TTF was remarkably elevated to 4.85%,but the use of DIO for the PBDT-T12-TTF-blend film resulted in a lower PCE of 0.91%.Atomic force microscopy(AFM)indicated that the superior efficiency of PBDT-T6-TTF with 3%DIO(v/v)should be related to the better continuous phase separation of the blend film.Nevertheless,the morphology of the PBDT-T12-TTF deteriorated when the 3%DIO(v/v)was added.Our results suggest that the alkyl-chain length on the 2D BDT units play an important role in determining the optoelectronic properties of dual 2D BDT-TT-based polymers.     

The first application of isoindigo-based polymers in non-fullerene organic solar cells

Although isoindigo(IID)-based polymers can realize high charge mobility, these materials are currently confined to fullerenebased organic solar cells(OSCs). Herein, we designed a pair of alternative D-π-A type copolymers, PE71 and PE72, to expand the application in non-fullerene OSCs, where benzo[1,2-b:4,5-b′]thiophene(BDT), thieno[3,2-b]thiophene(TT) and IID units were used as D, A and π-bridge, respectively. The aim of optimizing the length of alkyl chains on TT bridge is to ensure polymer solubility, crystallinity as well as miscibility with acceptor molecules. We find that PE71 and PE72 exhibit similar optical and electronic properties, but PE71 with shorter hexyl chain tends to aggregate into fiber-like structure. In the end, Y6 is selected as the electron acceptor because of suitable energy levels and complementary absorption spectrum. Finally, PE71:Y6 device realizes a power conversion efficiency(PCE) of 12.03%, which is obviously higher than that of PE72:Y6 device(9.74%) and is also the highest value for IID-based photovoltaic polymers. The charge transport, molecular aggregation, film morphology and energy loss analysis were systematically investigated. The improved photovoltaic performance of PE71:Y6 mainly originates from the better interpenetrating network structure toward facilitating exciton seperation and free charge carrier transportation.Our results indicate that IID-based D-π-A polymers can also be utilized in non-fullerene OSCs and the alkyl chains on the thieno[3,2-b]thiophene π-bridge have a vital effect on the photovoltaic performance.     

Realizing over 10% efficiency in polymer solar cell by device optimization

The low band gap polymer based on benzodithiophene(BDT)-thieno[3,4-b]thiophene(TT)backbone,PBDT-TS1,was synthesized following our previous work and the bulk heterojunction(BHJ)material comprising PBDT-TS1/PC71BM was optimized and characterized.By processing the active layer with different additives i.e.1,8-diiodooctane(DIO),1-chloronaphthalene(CN)and 1,8-octanedithiol(ODT)and optimizing the ratio of each additive in the host solvent,a high PCE of 9.98%was obtained under the condition of utilizing 3%DIO as processing additive in CB.The effect of varied additives on photovoltaic performance was illustrated with atomic force microscopy(AFM)and transmission electron microscope(TEM)measurements that explained changes in photovoltaic parameters.These results provide valuable information of solvent additive choice in device optimization of PBDTTT polymers,and the systematic device optimization could be applied in other efficient photovoltaic polymers.Apparently,this work presents a great advance in single junction PSCs,especially in PSCs with conventional architecture.     

Multiresponsive Polymer Assemblies Achieved by a Subtle Chain Terminal Modification

Inspired by the influence of chemical structure of end groups on the phase transition temperature of thermoresponsive polymers,we demonstrated a strategy to control the multi-responsiveness of polymer assemblies via subtle modification of end groups of thermoresponsive polymer segments and revealed its potential application for drug delivery.By developing polymer assemblies composed of poly(aliphatic ester) as the inner core and thermoresponsive polyphosphoester as the outer shell,we showed that end groups of thermoresponsive polyphosphoester segments controlled the surface property of assemblies and further determined the stimuli-responsive behavior.The phase-transition temperatures of the unmodified polymer assemblies are tightly controlled by their surface properties due to the hydrophilic to hydrophobic transitions of end groups in response to an environmental stimulus (e.g.pH or light irradiation).External control over these surface properties can by asserted by adjusting the chemical structure and composition of the terminal groups of the thermoresponsive polyphosphoesters.     

High-performance all-polymer solar cells enabled by a novel low bandgap non-fully conjugated polymer acceptor

The non-fully conjugated polymer as a new class of acceptor materials has shown some advantages over its small molecular counterpart when used in photoactive layers for all-polymer solar cells(all-PSCs), despite a low power conversion efficiency(PCE)caused by its narrow absorption spectra. Herein, a novel non-fully conjugated polymer acceptor PFY-2 TS with a low bandgap of~1.40 eV was developed, via polymerizing a large π-fused small molecule acceptor(SMA) building block(namely YBO) with a nonconjugated thioalkyl linkage. Compared with its precursor YBO, PFY-2 TS retains a similar low bandgap but a higher LUMO level.Moreover, compared with the structural analog of YBO-based fully conjugated polymer acceptor PFY-DTC, PFY-2 TS shows a similar absorption spectrum and electron mobility, but significantly different molecular crystallinity and aggregation properties,which results in optimal blend morphology with a polymer donor PBDB-T and physical processes of the device in all-PSCs. As a result, PFY-2 TS-based all-PSCs achieved a PCE of 12.31% with a small energy loss of 0.56 eV enabled by the reduced non-radiative energy loss(0.24 eV), which is better than that of 11.08% for the PFY-DTC-based ones. Our work clearly demonstrated that non-fully conjugated polymers as a new class of acceptor materials are very promising for the development of high-performance all-PSCs.     

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/cm² 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/cm²,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.