Alcohol-dispersed polymer complex as an effective and durable interface modifier for n-i-p perovskite solar cells

Abundant interfacial defects remain a significant challenge that hampers both the efficiency and stability of perovskite solar cells(PSCs).Herein,an alcohol-dispersed conducting polymer complex,denoted as PEDOT:F(Poly(3,4-ethylene dioxythiophene):Perfluorinated sulfonic acid ionomers),is introduced into the interface between perovskite and hole transporting layer in regular-structured PSCs.PEDOT:F serves as a multi-functional interface layer(filling grain boundaries and covering perovskite's grain-surface)to achieve a robust interaction with organic groups within perovskites,which could induce a structural transformation of PEDOT to increase its conductivity for the efficient hole-transport.Furthermore,the strong interaction between PEDOT and perovskites could promote an effective coupling of undercoordinated Pb~(2+)ions with the lone electron pairs near O&S atoms in PEDOT molecules,thereby enhancing defect passivation.Additionally,PEDOT:F with inherent hydrophobic properties prevents effectively moisture invasion into perovskites for the improved long-term stability of the PSCs.Consequently,the PEDOT:F-based PSCs achieved a champion efficiency of 24.81%,and maintained ca.92%of their initial efficiency after 7680 h of storage in a dry air environment,accompanied by the enhanced photothermal stability.

A novel perylene diimide-based ionene polymer and its mixed cathode interlayer strategy for efficient and stable inverted perovskite solar cells

Inverted(p-i-n)perovskite solar cells(PerSCs)have attracted much attention owing to their low temperature processability,less hysteresis effect and easy integration as a subunit for the tandem device.The unsatisfactory interface contacts and energy level barrier between adjacent interlayers on the cathode side are one of the key challenges for the development of p-i-n PerSCs.Herein,perylene diimidebased(PDI)ionene polymer was synthesized and developed as a cathode interlayer(CIL)to enhance interface contact,reduce the energy level barrier and prevent the migration of I-ions.The compact PNPDI CIL with high conductivity and appropriate lowest unoccupied molecular orbital(LUMO)level,resulted in a high efficiency device(20.03%),which is higher than the control device with bathophenanthroline(Bphen)(19.48%).Bphen-based CIL shows better adjusting ability of the work function of cathode metal but exhibits poor film-forming property.So,the synergistic effect of 1+1>2 can be obtained by combining Bphen and PNPDI into one CIL.As expected,the device performance was further improved by using the mixed CIL of Bphen and PNPDI,and 21.46%power conversion efficiency(PCE)was achieved.What’s more,the compact and hydrophobic mixed CIL dramatically enhanced the resistance to I-ions and moisture,which led to much enhanced device stability.

A new perspective to develop regiorandom polymer acceptors with high active layer ductility,excellent device stability,and high efficiency approaching 17%

The recently reported efficient polymerized small-molecule acceptors(PSMAs)usually adopt a regioregular backbone by polymerizing small-molecule acceptors precursors with a low-reactivity 5-brominated 3-(dicyanomethylidene)indan-1-one(IC)end group or its derivatives,leading to low molecular weight,and thus reduce active layer mechanical properties.Herein,a series of newly designed chlorinated PSMAs originating from isomeric IC end groups are developed by adjusting chlorinated positions and copolymerized sites on end groups to achieve high molecular weight,favorable intermolecular interaction,and improved physicochemical properties.Compared with regioregular PY2Se-Cl-o and PY2Se-Cl-m,regiorandom PY2Se-Cl-ran has a similar absorption profile,moderate lowest unoccupied molecular orbital level,and favorable intermolecular packing and crystallization properties.Moreover,the binary PM6:PY2Se-Cl-ran blend achieves better ductility with a crack-onset strain of 17.5% and improved power conversion efficiency(PCE)of 16.23% in all-polymer solar cells(all-PSCs)due to the higher molecular weight of PY2Se-Cl-ran and optimized blend morphology,while the ternary PM6:J71:PY2Se-Cl-ran blend offers an impressive PCE approaching 17% and excellent device stability,which are all crucial for potential practical applications of all-PSCs in wearable electronics.To date,the efficiency of 16.86% is the highest value reported for the regiorandom PSMAs-based all-PSCs and is also one of the best values reported for the all-PSCs.Our work provides a new perspective to develop efficient all-PSCs,with all high active layer ductility,impressive PCE,and excellent device stability,towards practical applications.

Improved performance of polymer solar cells by using inorganic, organic, and doped cathode buffer layers

The interface between the active layer and the electrode is one of the most critical factors that could affect the device performance of polymer solar cells. In this work, based on the typical poly（3-hexylthiophene）：[6,6]-phenyl C61-butyric acid methyl ester （P3HT：PCBM） polymer solar cell, we studied the effect of the cathode buffer layer （CBL） between the top metal electrode and the active layer on the device performance. Several inorganic and organic materials commonly used as the electron injection layer in an organic light-emitting diode （OLED） were employed as the CBL in the P3HT：PCBM polymer solar cells. Our results demonstrate that the inorganic and organic materials like Cs2CO3, bathophenanthroline （Bphen）, and 8-hydroxyquinolatolithium （Liq） can be used as CBL to efficiently improve the device performance of the P3HT：PCBM polymer solar cells. The P3HT：PCBM devices employed various CBLs possess power conversion efficiencies （PCEs） of 3.0%-3.3%, which are ca. 50% improved compared to that of the device without CBL. Furthermore, by using the doped organic materials Bphen：Cs2CO3 and Bphen：Liq as the CBL, the PCE of the P3HT：PCBM device will be further improved to 3.5%, which is ca. 70% higher than that of the device without a CBL and ca. 10% increased compared with that of the devices with a neat inorganic or organic CBL.

Effect of imidazole based polymer blend electrolytes for dye-sensitized solar cells in energy harvesting window glass applications

The exploration of polymer electrolyte in the field of dye sensitized solar cell(DSSC) can contribute to increase the invention of renewable energy applications. In the present work, the influence of imidazole on the poly(vinylidene fluoride)(PVDF)–poly(methyl methacrylate)(PMMA)–Ethylene carbonate(EC)–KI–I2 polymer blend electrolytes has been evaluated. The different weight percentages of imidazole added into polymer blend electrolytes have been prepared by solution casting. The prepared films were characterized by Fourier transform infrared spectroscopy(FTIR), X-ray diffraction(XRD), thermogravimetric analysis(TGA), UV–visible spectra, photoluminescence spectra and impedance spectroscopy. The surface roughness texture of the film was analyzed by atomic force microscopy(AFM). The ionic conductivity of the optimized polymer blend electrolyte was determined by impedance measurement, which is 1.95 × 10-3 S·cm-1 at room temperature. The polymer electrolyte containing 40 wt% of imidazole content exhibits the highest photo-conversion efficiency of 3.04%under the illumination of 100 m W·cm-2. Moreover, a considerable enhancement in the stability of the DSSC device was demonstrated.

Nanomorphology in A–D–A type small molecular acceptors-based bulk heterojunction polymer solar cells

Recent developments in acceptor–donor–acceptor(A–D–A) type non-fullerene acceptors have led to substantial improvements in bulk-heterojunction polymer solar cells efficiency. The device performance strongly depends on photoactive layer morphology, as the molecular packing, donor–acceptor interface and phase separation significantly affect the charge-transfer states and charge carrier dynamics. In this review, we start with a brief introduction of the techniques most effectively utilized to characterize multiphase morphology. Then, we summarize recent progress in A–D–A type acceptors, with the emphasis on understanding the molecular structure–morphology–performance relationships. Finally, an outlook on correlating morphological characteristics with photovoltage losses is presented for further improving device performance.

Novel polymer acceptors achieving 10.18% efficiency for all-polymer solar cells

Polymer acceptors based on extended fused ring p skeleton has been proven to be promising candidates for all-polymer solar cells(all-PSCs), due to their remarkable improved light absorption than the traditional imide-based polymer acceptors. To expand structural diversity of the polymer acceptors, herein,two polymer acceptors PSF-IDIC and PSi-IDIC with extended fused ring p skeleton are developed by copolymerization of 2,20-((2 Z,20 Z)-((4,4,9,9-tetrahexadecyl-4,9-dihydro-s-indaceno [1,2-b:5,6-b']dithio phene-2,7-diyl)bis(methanylylidene))bis(3-oxo-2,3-dihydro-1 H-indene-2,1-diylidene))dimalononitrile(IDIC-C16) block with sulfur(S) and fluorine(F) functionalized benzodithiophene(BDT) unit and silicon(Si) atom functionalized BDT unit, respectively. Both polymer acceptors exhibit strong light absorption.The PSF-IDIC exhibits similar energy levels and slightly higher absorption coefficient relative to the PSi-IDIC. After blended with the donor polymer PM6, the functional atoms on the polymer acceptors show quite different effect on the device performance. Both of the acceptors deliver a notably high open circuit voltage(V_(OC)) of the devices, but PSi-IDIC achieves higher V OCthan PSF-IDIC. All-PSC based on PM6:PSi-IDIC attains a power conversion efficiency(PCE) of 8.29%, while PM6:PSF-IDIC-based device achieves a much higher PCE of 10.18%, which is one of the highest values for the all-PSCs reported so far. The superior device performance of PM6:PSF-IDIC is attributed to its higher exciton dissociation and charge transport, decreased charge recombination, and optimized morphology than PM6:PSi-IDIC counterpart. These results suggest that optimizing the functional atoms of the side chain provide an effective strategy to develop high performance polymer acceptors for all-PSCs.

Properties of Plasma Enhanced Chemical Vapor Deposition Barrier Coatings and Encapsulated Polymer Solar Cells

In this paper, we report silicon oxide coatings deposited by plasma enhanced chem- ical vapor deposition technology （PECVD） on 125 pm polyethyleneterephthalate （PET） surfaces for the purpose of the shelf lifetime extension of sealed polymer solar cells. After optimiza- tion of the processing parameters, we achieved a water vapor transmission rate （WVTR） of ca. 10-a g/m2/day with the oxygen transmission rate （OTR） less than 0.05 cc/m2/day, and succeeded in extending the shelf lifetime to about 400 h in structure of coatings related to the properties of encapsulated solar cells. And then the chemical encapsulated cell was investigated in detail

CONTROLLING THE 3D NANOSCALE ORGANIZATION OF BULK HETEROJUNCTION POLYMER SOLAR CELLS

In this study,the three dimensional nanoscale organization in the photoactive layers of poly(3-hexylthiophene) (P3HT) and a methanofullerene derivative (PCBM) is revealed by transmission electron tomography.After annealing treatment,either at elevated temperature or during slow solvent evaporation,nanoscale interpenetrating networks are formed with high crystalline order and favorable concentration gradients of both components through the thickness of the photoactive layer.Such a tailored morphology account...

Inverted polymer solar cells with employing of electrochemical-anodizing synthesized TiO_2 nanotubes

An inverted structure of polymer solar cells based on Poly（3-hexylthiophene）（P3HT）：[6-6] Phenyl-（6） butyric acid methyl ester （PCBM） with using thin films of TiO2 nanotubes and nanoparticles as an efficient cathode buffer layer is developed. A total of three cells employing TiO2 thin films with different thickness values are fabricated. Two cells use layers of TiO2 nanotubes prepared via self-organized electrochemical-anodizing leading to thickness values of 203 and 423.7 nm, while the other cell uses only a simple sol-gel synthesized TiO2 thin film of nanoparticles with a thickness of 100 nm as electron transport layer. Experimental results demonstrate that TiO2 nanotubes with these thickness values are inefficient as the power conversion efficiency of the cell using 100-nm TiO2 thin film is 1.55%, which is more than the best power conversion efficiency of other cells. This can be a result of the weakness of the electrochemical anodizing method to grow nanotubes with lower thickness values. In fact as the TiO2 nanotubes grow in length the series resistance （Rs） between the active polymer layer and electron transport layer increases, meanwhile the fill factor of cells falls dramatically which finally downgrades the power conversion efficiency of the cells as the fill factor falls.

Improving the performance of polymer solar cells by adjusting the crystallinity and nanoscale phase separation

In this paper, we report a high-perfornmnce P3HT/PCBM bulk-heterojunction solar cell with a power conversion efficiency of 4.85% fabricated by adjusting the polymer crystallinity and nanoscale phase separation using an ultrasonic irradiation mixing approach for the polymer. The grazing incidence X-ray diffraction, UV/Vis spectroscopic, and atomic force microscopic measurement results for the P3HT/PCBM blend films reveal that the P3HT/PCBM film fabricated by ultrasonic irradiation mixing of the P3HT and PCBM solutions for 10 min has a higher degree of crystallinity, a higher absorption efficiency, and better phase separation, which together account for the higher charge transport properties and photovoltaic cell performance.

Efficiency Enhancement of Inverted Polymer Solar Cells Using Ionic Liquid-functionalized Carbon Nanoparticles-modified ZnO as Electron Selective Layer

ZnO thin film was fabricated on tin-doped indium oxide electrode as an electron selective layer of inverted polymer solar cells using magnetron sputtering deposition. Ionic liquid-functionalized carbon nanoparticles(ILCNs) film was further deposited onto ZnO surfaces by drop-casting ILCNs solution to improve interface properties. The power conversion efficiency(PCE) of inverted polymer solar cells(PSCs)with only ZnO layer was quickly decreased from 2.7% to 2.2% when the thickness of ZnO layer was increased from 15 nm to 60 nm. However, the average PCE of inverted PSCs with ZnO layer modified with ILCNs only decreased from 3.5% to 3.4%, which is comparable to that of traditional PSCs with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) anode buffer layer. The results suggested that the contact barrier between ZnO layer and poly(3-hexylthiophene) and phenyl-C61-butyric acid methylester(P3HT:PCBM)blended film compared to ZnO bulk resistance can more significantly influence the performance of inverted PSCs with sputtered ZnO layer. The vanishment of negative capacitive behavior of inverted PSCs with ILCNs modified ZnO layer indicated ILCNs can greatly decrease the contact barrier of ZnO/P3HT:PCBM interface.

Chlorinated polymer solar cells simultaneously enhanced by fullerene and non-fullerene ternary strategies

To achieve efficient polymer solar cells(PSCs)with full utilization of the whole spectrum,the multicomponent devices are of great importance to be deeply explored,especially for their capability of one-step fabrication.However,the research about one same binary system simultaneously derivated various multi-component PSC is still very limited.Herein,we achieved the whole constructions from one binary host to different ternary systems and even the quaternary one.The ternary strategies with fullerene acceptor,PC_(71)BM,and non-fullerene acceptor,BT_(6)IC-BO-4Cl,as the third component,both boosted the device efficiencies of PBT4Cl-Bz:IT-4F binary system from about 9% to comparatively beyond 11%.Despite the comparable improvement of performance,there existed other similarities and differences in two ternary strategies.In detail,the isotropic carrier transport of PC_(71)BM which largely elevated the fill factor(FF)in the corresponding devices,while the strong absorption of BT_(6)IC-BO-4Cl enhanced the short current density(J_(SC))most.More interestingly,quaternary devices based on PBT4Cl-Bz:IT-4F:PC71 BM:BT_(6)IC-BO-4Cl could combine both advantages of fullerene and non-fullerene ternary strategies,further pumped the J_(SC) from 16.44 to the highest level of 19.66 mA cm^(-2) among all devices,eventually resulted in an optimized efficiency of 11.69%.It reveals that both fullerene and non-fullerene ternary strategies have their unique feature to elevate the device performance either by efficient isotropic carrier transport or better coverage of whole sunlight spectrum and easy tunable energy levels from organic materials.The key is how to integrate the two pathways in one system and provide a more competitive solution facing high-quality PSCs.

N-alkyl chain modification in dithienobenzotriazole unit enabled efficient polymer donor for high-performance non-fullerene solar cells

Molecular design of either polymer donors or acceptors is a promising strategy to tune the morphology of the active layer of organic solar cells,enabling a high-performance device.Thereinto,developing novel polymer donors is an alternative method to obtain high photovoltaic performance.Herein,we present a facile side-chain engineering on the dithiophenobenzotriazole(DTBTz)unit of newly-designed polymer donors(named p BDT-DTBTz-EH and p BDT-DTBTz-Me)to boost the performance of non-fullerene solar cells.Compared with p BDT-DTBTz-EH with long N-alkyl side chains,p BDT-DTBTz-Me with a short methyl exhibits stronger molecular aggregation,higher absorption coefficient,and preferred face-on orientation packing.As a consequence,p BDT-DTBTz-Me based devices achieve an optimal power conversion efficiency of 15.31%when donors are paired with the narrow bandgap acceptor Y6,which is superior to that of p BDT-DTBTz-EH based devices(9.17%).Additionally,the p BDT-DTBTz-Me based devices manifest more effective charge separation and transfer than p BDT-DTBTz-EH based devices.These results indicate that fine-tuning side chains of polymer donors provide new insights for the design of high-performance polymer donors in non-fullerene solar cells.

Shorter alkyl chain in thieno[3,4-c]pyrrole-4,6-dione(TPD)-based large bandgap polymer donors – Yield efficient non-fullerene polymer solar cells

Typically,conjugated polymers are composed of conjugated backbones and alkyl side chains.In this contribution,a cost-effective strategy of tailoring the length of alkyl side chain is utilized to design highperforming thieno[3,4-c]pyrrole-4,6-dione(TPD)-based large bandgap polymer donors PBDT-BiTPD(Cχ)(χ=48,52,56),in which x represents the alkyl side chain length in term of the total carbon number.A combination of light absorption,device,and morphology examinations make clear that the shorter alkyl side chains yield(i) higher crystallinity and more predominant face-on crystallite orientation in their neat and BHJ blend films,(ii) higher charge mobilities(6.7×10^(-4) cm~2 V^(-1) s^(-1) for C48 vs.3.2×10^(-4) cm~2 V^(-1) s^(-1) for C56),and negligible charge recombination,consequently,(iii) significantly improved fill-factor(FF) and short current(J_(SC)),while almost the same open circuit voltage(V_(OC)) of ca.0.82 V in their corresponding BHJ devices.In parallel,as alkyl side chain lengths decrease from C56 to C48,power conversion efficiencies(PCEs) increased from 7.8% for C56 to 11.1% for C52,and further to14.1% for C48 in their BHJ solar cells made with a narrow bandgap non-fullerene acceptor Y6.This systematic study declares that shortening the side chain,if providing appropriate solubility in device solution processing solvents,is of essential significance for developing high-performing polymer donors and further improving device photovoltaic performance.

Non-conjugated polymers as thickness-insensitive electron transport materials in high-performance inverted organic solar cells

Two non-conjugated polymers PEIE-DBO and PEIE-DCO, prepared by quaternization of polyethyleneimine ethoxylate by 1,8-dibromooctane and 1,8-dichlorooctane respectively, are developed as electron transport layer(ETL) in high-performance inverted organic solar cells(OSCs), and the effects of halide ions on polymeric photoelectric performance are fully investigated. PEIE-DBO possesses higher electron mobility(3.68×10-4 cm2 V-1s-1), higher conductivity and more efficient exciton dissociation and electron extraction, attributed to its lower work function(3.94 eV) than that of PEIE-DCO, which results in better photovoltaic performance in OSCs. The inverted OSCs with PTB7-Th: PC71BM as photoactive layer and PEIE-DBO as ETL exhibit higher PCE of 10.52%, 9.45% and 9.09% at the thickness of 9, 35 and 50 nm,respectively. To our knowledge, PEIE-DBO possesses the best thickness-insensitive performance in polymeric ETLs of inverted fullerene-based OSCs. Furthermore, PEIE-DBO was used to fabricate the inverted non-fullerene OSCs(PM6:Y6) and obtained a high PCE of 15.74%, which indicates that PEIE-DBO is effective both in fullerene-based OSCs and fullerene-free OSCs.

Effects of Flexible Conjugation-Break Spacers of Non-Conjugated Polymer Acceptors on Photovoltaic and Mechanical Properties of All-Polymer Solar Cells

All-polymer solar cells(all-PSCs)possess attractive merits including superior thermal stability and mechanical flexibility for large-area roll-to-roll processing.Introducing flexible conjugation-break spacers(FCBSs)into backbones of polymer donor(P_(D))or polymer acceptor(P_(A))has been demonstrated as an efficient approach to enhance both the photovoltaic(PV)and mechanical properties of the all-PSCs.However,length dependency of FCBS on certain all-PSC related properties has not been systematically explored.In this regard,we report a series of new non-conjugated P_(A)s by incorporating FCBS with various lengths(2,4,and 8 carbon atoms in thioalkyl segments).Unlike com-mon studies on so-called side-chain engineering,where longer side chains would lead to better solubility of those resulting polymers,in this work,we observe that the solubilities and the resulting photovoltaic/mechanical properties are optimized by a proper FCBS length(i.e.,C2)in P_(A) named PYTS-C2.Its all-PSC achieves a high efficiency of 11.37%,and excellent mechanical robustness with a crack onset strain of 12.39%,significantly superior to those of the other P_(A)s.These results firstly demonstrate the effects of FCBS lengths on the PV performance and mechanical properties of the all-PSCs,providing an effective strategy to fine-tune the structures of P_(A)s for highly efficient and mechanically robust PSCs.

Modeling and implementation of tandem polymer solar cells using wide-bandgap front cells

Tandem device architectures offer a route to greatly increase the maximum possible power conversion efficiencies(PCEs)of polymer solar cells,however,the complexity of tandem cell device fabrication(such as selecting bandgaps of the front and back cells,current matching,thickness,and recombination layer optimization)often result in lower PCEs than are observed in single-junction devices.In this study,we analyze the influence of front cell and back cell bandgaps and use transfer matrix modeling to rationally design and optimize effective tandem solar cell structures before actual device fabrication.Our approach allows us to estimate tandem device parameters based on known absorption coefficients and open-circuit voltages of different active layer materials and design devices without wasting valuable time and materials.Using this approach,we have investigated a series of wide bandgap,high voltage photovoltaic polymers as front cells in tandem devices with PTB7-Th as a back cell.In this way,we have been able to demonstrate tandem devices with PCE of up to 12.8%with minimal consumption of valuable photoactive materials in tandem device optimization.This value represents one of the highest PCE values to date for fullerene-based tandem solar cells.

Phenylfluorenamine-functionalized poly(N-vinylcarbazole)s as dopant-free polymer hole-transporting materials for inverted quasi-2D perovskite solar cells

In order to improve the efficiency and stability of inverted three-dimensional(3D) or quasi-2D perovskite solar cells(PSCs) for future commercialization, exploring high efficient dopant-free polymer holetransporting materials(HTMs) is still desired and meaningful. One simple and efficient way to achieve high performance dopant-free HTMs is to synthesize novel non-conjugated side-chain polymers via rational molecular design. In this work, N-(4-methoxyphenyl)-9,9-dimethyl-9H-fluoren-2-amine(FMeNPh) groups are introduced into the poly(N-vinylcarbazole)(PVK) side chains to afford two nonconjugated polymers PVCz-DFMeNPh and PVCz-FMeNPh as dopant-free HTMs in inverted quasi-2D PSCs. Benefited from the flexible properties of polyethylene backbone and excellent optoelectronic natures of FMeNPh side-chain groups, PVCz-DFMeNPh with more FMeNPh units exhibited excellent thermal stability, well-matched energy levels and improved charge mobility as compared to PTAA and PVCzFMeNPh. Moreover, the morphologies investigation of quasi-2D perovskite on PVCz-DFMeNPh shows more compact and homogeneous perovskite films than those on PTAA and PVCz-FMeNPh. As a result,the dopant-free PVCz-DFMeNPh based inverted quasi-2D PSCs deliver power conversion efficiency(PCE) up to 18.44% as well as negligible hysteresis and favorable long-term stability, which represents as excellent performance reported to date for inverted quasi-2D PSCs. The results demonstrate the great potentials of constructing non-conjugated side-chain polymer HTMs based on phenylfluorenamine-func tionalized PVK for the development of high efficient and stable inverted 3D or quasi-2D PSCs.

Recent advances and prospects of asymmetric non-fullerene small molecule acceptors for polymer solar cells

Recently,polymer solar cells developed very fast due to the application of non-fullerence acceptors.Substituting asymmetric small molecules for symmetric small molecule acceptors in the photoactive layer is a strategy to improve the performance of polymer solar cells.The asymmetric design of the molecule is very beneficial for exciton dissociation and charge transport and will also fine-tune the molecular energy level to adjust the open-circuit voltage(Voc)further.The influence on the absorption range and absorption intensity will cause the short-circuit current density(Jsc)to change,resulting in higher device performance.The effect on molecular aggregation and molecular stacking of asymmetric structures can directly change the microscopic morphology,phase separation size,and the active layer's crystallinity.Very recently,thanks to the ingenious design of active layer materials and the optimization of devices,asymmetric non-fullerene polymer solar cells(A-NF-PSCs)have achieved remarkable development.In this review,we have summarized the latest developments in asymmetric small molecule acceptors(A-NF-SMAs)with the acceptor-donor-acceptor(A-D-A)and/or acceptor-donor-acceptor-donor-acceptor(A-D-A-D-A)structures,and the advantages of asymmetric small molecules are explored from the aspects of charge transport,molecular energy level and active layer accumulation morphology.