Enhancing efficiency and stability of organic solar cells through a simplified four-step synthesis of fully non-fused ring electron acceptor

Design and synthesis of superior cost-effective non-fullerene acceptors(NFAs)are still big challenges for facilitating the commercialization of organic solar cells(OSCs),yet to be realized.Herein,two medium bandgap fully non-fused ring electron acceptors(NFREAs,medium bandgap,i,e.,1,3-1,8 eV),namely PTR-2Cl and PTR-4Cl are synthesized with only four steps by using intramolecular noncovalent interaction central core,structured alkyl side chain orientation linking units and flanking with different electron-withdrawing end group.Among them,PTR-4C1 exhibits increased average electrostatic potential(ESP)difference with polymer donor,enhanced crystallinity and compactπ-πstacking compared with the control molecule PTR-2CI.As a result,the PTR-4Cl-based OSC achieved an impressive power conversion efficiency(PCE)of 14.72%,with a much higher open-circuit voltage(V_(OC))of 0.953 V and significantly improved fill factor(FF)of 0.758,demonstrating one of the best acceptor material in the top-performing fully NFREA-based OSCs with both high PCE and V_(OC).Notably,PTR-4Cl-based cells maintain a good T_80lifetime of its initial PCE after over 936 h under a continuous thermal annealing treatment and over1300 h T_(80)lifetime without encapsulation.This work provides a cost-effective design strategy for NFREAs on obtaining high V_(OC),efficient exciton dissociation,and ordered molecular packing and thus high-efficiency and stable OSCs.

Crystallization and Orientation Modulation Enable Highly Efficient Doctor-Bladed Perovskite Solar Cells

With the rapid rise in perovskite solar cells(PSCs)performance,it is imperative to develop scalable fabrication techniques to accelerate potential commercialization.However,the power conversion efficiencies(PCEs)of PSCs fabricated via scalable two-step sequential deposition lag far behind the state-of-the-art spin-coated ones.Herein,the additive methylammonium chloride(MACl)is introduced to modulate the crystallization and orientation of a two-step sequential doctorbladed perovskite film in ambient conditions.MACl can significantly improve perovskite film quality and increase grain size and crystallinity,thus decreasing trap density and suppressing nonradiative recombination.Meanwhile,MACl also promotes the preferred face-up orientation of the(100)plane of perovskite film,which is more conducive to the transport and collection of carriers,thereby significantly improving the fill factor.As a result,a champion PCE of 23.14%and excellent longterm stability are achieved for PSCs based on the structure of ITO/SnO_(2)/FA_(1-x)MA_xPb(I_(1-y)Br_y)_3/Spiro-OMeTAD/Ag.The superior PCEs of 21.20%and 17.54%are achieved for 1.03 cm~2 PSC and 10.93 cm~2 mini-module,respectively.These results represent substantial progress in large-scale two-step sequential deposition of high-performance PSCs for practical applications.

Copper naphthalocyanine-based hole-transport material for highperformance and thermally stable perovskite solar cells

Metal phthalocyanines(MPcs) have gained considerable research attention as hole-transport materials(HTMs) in perovskite solar cells(PSCs) because of their superb stability. However, the photovoltaic performance of MPc-based HTMs in PSCs is still lagging behind their small molecule and polymeric counterparts, largely due to their relatively low hole mobility. Here, we report for the first time the application of a copper naphthalocyanine derivative(namely t Bu-Cu Nc) as a hole-transport material(HTM)in perovskite solar cells(PSCs), and systematically study its optoelectronic and photovoltaic property compared with its Cu Pc analog(t Bu-Cu Pc). Combined experiments disclose that the extension of π-conjugation from Pc to Nc core leads to not only an enhanced hole-carrier mobility associated with a stronger intermolecular interaction, but also an elevated glass transition temperature(T_g) of 252 °C. The resultant PSCs employing t Bu-Cu Nc deliver an excellent power conversion efficiency of 24.03%, which is the record efficiency reported for metal complex-based HTMs in PSCs. More importantly, the encapsulated t Bu-Cu Nc-based devices also show dramatically improved thermal stability than the devices using the well-known SpiroOMe TAD, with a T_(80)lifetime for more than 1,000 h under damp-heat stress. This study unfolds a new avenue for developing efficient and stable HTMs in PSCs.

Bridging buried interface enable 24.67%-efficiency doctor-bladed perovskite solar cells in ambient condition

Scalable deposition of high-efficiency perovskite solar cells(PSCs)is critical to accelerating their commercial applications.However,a significant number of defects are distributed at the buried interface of perovskite film fabricated by scalable deposition,exhibiting much negative influence on the efficiency and stability of PSCs.Herein,2-(N-morpholino)ethanesulfonic acid potassium salt(MESK)is incorporated as the bridging layer between the tin oxide(SnO_(2))electron transport layer(ETL)and the perovskite film deposited via scalable two-step doctor blading.Both experiment and simulation results demonstrate that MESK can passivate the trap states of Sn suspension bonds,thereby enhancing the charge extraction and transport of the SnO_(2)ETL.Meanwhile,the strong interaction with uncoordinated Pb ions can modulate the crystal growth and crystallographic orientation of perovskite film and passivate buried defects.With employing MESK interface bridging,PSCs fabricated via scalable doctor blading in ambient condition achieve a power conversion efficiency(PCE)of 24.67%,which is one of the highest PCEs for doctor-bladed PSCs,and PSC modules with an active area of 11.35 cm^(2)achieve a PCE of 19.45%.Furthermore,PSCs exhibit excellent long-term stability,and the unpackaged target device with a storage of 1680 h in ambient condition(25℃and humidity of 30%relative humidity(RH))can maintain more than 90%of the initial PCE.The research provides a strategy for constructing a high-performance interface bridge between SnO_(2)ETL and perovskite film,and achieving efficient and stable large-area PSCs and modules fabricated via scalable doctor-blading process in ambient condition.

Revealing the vertical structure of in-situ fabricated perovskite nanocrystals films toward efficient pure red light-emitting diodes

The development of efficient perovskite light-emitting diodes(PeLEDs)relies strongly on the fabrication of perovskite films with rationally designed structures(grain size,composition,surface,etc.).Therefore,an understanding of structure-performance relationships is of vital importance for developing high-performance perovskite devices,particularly for devices with in-situ fabricated perovskite nanocrystal films.In this study,we reveal the vertical structure of an in-situ fabricated quasi-two-dimensional perovskite film.By combining time-of-flight secondary ion mass spectrometry,energy dispersive spectroscopy,grazing incidence wide-angle X-ray scattering(GIWAXS),and low-temperature photoluminescence spectra,we illustrate that the resulting in-situ fabricated DPPA_(2)Cs_(n-1)Pb_(n)(Br_(0.3)I_(0.7))_(3n+1)(DPPA^(+):3,3-diphenylpropylammonium)film has a gradient structure with a very thin layer of ligands on the surface,predominantly small-n domains at the top,and predominantly large-n domains at the bottom owing to the solubility difference of the precursors.In addition,GIWAXS measurements show that the domain of n=2 on the top layer has an ordered in-plane alignment.Based on the understanding of the film structure,we developed an in-situ fabrication process with ligand exchange to achieve efficient pure red PeLEDs at 638 nm with an average external quantum efficiency(EQE)of 7.4%.The optimized device had a maximum luminance of 623 cd/m^(2) with a peak EQE of 9.7%.

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.

Strong circularly polarized luminescence from quantum dots/2D chiral perovskites composites

Chiral perovskites(CPs)have attracted enormous attentions since they have combined chirality and optoelectrical properties well which is promising in circularly polarized luminescence(CPL)application and of great importance for future spin-optoelectronics.However,there is a key contradiction that in chiral perovskites chirality distorts the crystal structure,leading to poor photoluminescence(PL)properties.Achieving the balance between chirality and PL is a major challenge for strong CPL from chiral perovskites.Differently,two-dimensional(2D)chiral perovskite has shown fascinating chiral induced spin selectivity(CISS)effect which can act as spin injector under ambient conditions.Here,we propose an effective strategy to achieve high CPL activity generated from quantum dots(QDs)by introducing 2D chiral perovskite as a chiral source,providing spin polarized carriers through the CISS effect.The as-synthesized QDs/CP composites exhibit dissymmetry factors(glum)up to 9.06×10^(−3).For the first time,we performed grazing incident wide angle X-ray scattering(GIWAXS)measurements,showing the chirality originates from the distorted lattices caused by the large chiral organic cations.Besides,time-resolved PL(TR-PL)measurements verify the enhanced CPL activity should be attributed to the charge transport between two components.These findings provide a useful method to achieve CPL in QDs/2D chiral perovskite heterojunctions which could be promising in spinoptoelectronics application.

Origin of High Efficiency and Long-Term Stability in Ionic Liquid Perovskite Photovoltaic

Environment-friendly protic amine carboxylic acid ionic liquids(ILs)as solvents is a significant breakthrough with respect to traditional highly coordinating and toxic solvents in achieving efficient and stable perovskite solar cells(PSCs)with a simple one-step air processing and without an antisolvent treatment approach.However,it remains mysterious for the improved efficiency and stability of PSCs without any passivation strategy.Here,we unambiguously demonstrate that the three functions of solvents,additive,and passivation are present for protic amine carboxylic acid ILs.We found that the ILs have the capability to dissolve a series of perovskite precursors,induce oriented crystallization,and chemically passivate the grain boundaries.This is attributed to the unique molecular structure of ILs with carbonyl and amine groups,allowing for strong interaction with perovskite precursors by forming C=O…Pb chelate bonds and N-H…I hydrogen bonds in both solution and film.This finding is generic in nature with extension to a wide range of IL-based perovskite optoelectronics.

Hole-Transporting Low-Dimensional Perovskite for EnhancingPhotovoltaic Performance

Halide perovskites with low-dimensionalities(2D or quasi-2D)have demonstrated outstanding stabilities compared to their 3D counterparts.Nevertheless,poor charge-transporting abilities of organic components in 2D perovskites lead to relatively low power conversion efficiency(PCE)and thus limit their applications in photovoltaics.Here,we report a novel hole-transporting low-dimensional(HT2D)perovskite,which can form a hole-transporting channel on the top surface of 3D perovskite due to self-assembly effects of metal halide frameworks.This HT2D perovskite can significantly reduce interface trap densities and enhance hole-extracting abilities of a heterojunction region between the 3D perovskite and hole-transporting layer.Furthermore,the posttreatment by HT2D can also reduce the crystal defects of perovskite and improve film morphology.As a result,perovskite solar cells(PSCs)can effectively suppress nonradiative recombination,leading to an increasement on photovoltage to>1.20 V and thus achieving>20%power conversion efficiency and>500 h continuous illumination stability.This work provides a pathway to overcome charge-transporting limitations in low-dimensional perovskites and delivers significant enhancements on performance of PSCs.

Unveiling the Effects of Interchain Hydrogen Bonds on Solution Gelation and Mechanical Properties of Diarylfluorene-Based Semiconductor Polymers

The intrinsically rigid and limited strain of most conjugated polymers has encouraged us to optimize the extensible properties of conjugated polymers.Herein,learning from the hydrogen bonds in glucose,which were facilitated to the toughness enhancement of cellulose,we introduced interchain hydrogen bonds to polydiarylfluorene by amide-containing side chains.Through tuning the copolymerization ratio,we systematically investigated their influence on the hierarchical condensed structures,rheology behavior,tensile performances,and optoelectronic properties of conjugated polymers.Compared to the reference copolymers with a low ratio of amide units,copolymers with 30%and 40%amide units present a feature of the shearthinning process that resembled the non-Newtonian fluid,which was enabled by the interchain dynamic hydrogen bonds.Besides,we developed a practical and universal method for measuring the intrinsic mechanical properties of conjugated polymers.We demonstrated the significant impact of hydrogen bonds in solution gelation,material crystallization,and thin film stretchability.Impressively,the breaking elongation for P4 was even up to~30%,which confirmed the partially enhanced film ductility and toughness due to the increased amide groups.Furthermore,polymer light-emitting devices(PLEDs)based on these copolymers presented comparable performances and stable electroluminescence(EL).Thin films of these copolymers also exhibited random laser emission with the threshold as low as 0.52μJ/cm^(2),suggesting the wide prospective application in the field of flexible optoelectronic devices.