A multifunctional and scalable fullerene electron transporting material for efficient inverted perovskite solar cells and modules

The interfacial properties between charge transporting material and perovskite(PVSK)play critical roles in governing the photovoltaic performances of perovskite solar cells(PVSCs).Herein,we develop a multifunctional fulleropyrrolidine(FMG)as an electron transporting material(ETM),which facilitates the construction of efficient and stable inverted PVSCs and modules.It revealed that the facile and scalable FMG possesses not only excellent electron extraction capabilities,but also multi-groups to simultaneously passivate PVSKs via Lewis acid-base and hydrogen bonding interactions.The coating of FMG onto PVSK interestingly yields a dense and interactive layer with the graded ETM-PVSK heterojunction architecture.As a result,FMGbased PVSCs demonstrate a champion efficiency of 23.8%,outperforming 21.0%of PCBM-based devices.FMG could also be utilized to improve photovoltaic performance of large-scale modules.In addition,FMG has successfully elongated the lifetime of the corresponding PVSCs,maintaining 85%of the initial performance after the continuous 60-day one sun equivalent illumination in ambient.

Crystallographic Understanding of Photoelectric Properties for C_(60) Derivatives Applicable as Electron Transporting Materials in Perovskite Solar Cells

Hundreds of C60 derivatives stand out as electrontransporting materials(ETMs), for example, in perovskite solar cells(PSCs), due to their properties on electron extraction or defect passivation. However, it still lacks of guidelines to update C60-based ETMs with excellent photoelectric properties. In this work, crystallographic data of eight C60-based ETMs, including pristine C60 and the well-known PCBM as well as six newly synthesized fullerenes, are analyzed to establish the connections between derivatized structures and photoelectric properties for the typical carbon cluster of C60. In terms of packing centroid-centroid distance between neighboring carbon cages, the crystallographic data are useful for probing photoelectric properties, such as electrochemical properties, electron mobility and photovoltaic performances, and therefore facilitate to design novel C60-based ETMs for PSCs with high performances.

Toward high-efficiency perovskite solar cells with one-dimensional oriented nanostructured electron transport materials

The unique advantages of one-dimensional(1D)oriented nanostructures in light-trapping and chargetransport make them competitive candidates in photovoltaic(PV)devices.Since the emergence of perovskite solar cells(PSCs),1D nanostructured electron transport materials(ETMs)have drawn tremendous interest.However,the power conversion efficiencies(PCEs)of these devices have always significantly lagged behind their mesoscopic and planar counterparts.High-efficiency PSCs with 1D ETMs showing efficiency over 22%were just realized in the most recent studies.It yet lacks a comprehensive review covering the development of 1D ETMs and their application in PSCs.We hence timely summarize the advances in 1D ETMs-based solar cells,emphasizing on the fundamental and optimization issues of charge separation and collection ability,and their influence on PV performance.After sketching the classification and requirements for high-efficiency 1D nanostructured solar cells,we highlight the applicability of 1D TiO_(2)nanostructures in PSCs,including nanotubes,nanorods,nanocones,and nanopyramids,and carefully analyze how the electrostatic field affects cell performance.Other kinds of oriented nanostructures,e.g.,ZnO and SnO_(2)ETMs,are also described.Finally,we discuss the challenges and propose some potential strategies to further boost device performance.This review provides a broad range of valuable work in this fast-developing field,which we hope will stimulate research enthusiasm to push PSCs to an unprecedented level.

Spatial configuration engineering of perylenediimide-based non-fullerene electron transport materials for efficient inverted perovskite solar cells

Due to their excellent photoelectron chemical properties and suitable energy level alignment with perovskite,perylene diimide(PDI)derivatives are competitive non-fullerene electron transport material(ETM)candidates for perovskite solar cells(PSCs).However,the conjugated rigid plane structure of PDI units result in PDI-based ETMs tending to form large aggregates,limiting their application and photovoltaic performance.In this study,to restrict aggregation and further enhance the photovoltaic performance of PDI-type ETMs,two PDI-based ETMs,termed PDO-PDI2(dimer)and PDO-PDI3(trimer),were constructed by introducing a phenothiazine 5,5-dioxide(PDO)core building block.The research manifests that the optoelectronic properties and film formation property of PDO-PDI2 and PDO-PDI3 were deeply affected by the molecular spatial configuration.Applied in PSCs,PDO-PDI3 with threedimensional spiral molecular structure,exhibits superior electron extraction and transport properties,further achieving the best PCE of 18.72%and maintaining 93%of its initial efficiency after a 720-h aging test under ambient conditions.

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.

Highly soluble dendritic fullerene derivatives as electron transport material for perovskite solar cells

A series of shape-persistent polyphenylene dendritic C_(60)derivatives as the electron transport materials were designed and synthesized via a catalyst-free Diels-Alder[4+2]cycloaddition reaction.These increasing hyperbranched scaffolds could effectively enhance the solubility;notably,both first and second generation dendrimers,C_(60)-G1 and C_(60)-G2,demonstrated more than 5 times higher solubilities than pristine C_(60).Furthermore,both simulated and experimental data proved their promising solution-processabilities as electron-transporting layers(ETLs)for perovskite solar cells.As a result,the planar p-i-n structural perovskite solar cell could achieve a maximum power conversion efficiency of 14.7%with C_(60)-G2.

Thermionic electron emission in the 1D edge-to-edge limit

Thermionic emission is a tunneling phenomenon,which depicts that electrons on the surface of a conductor can be pulled out into the vacuum when they are subjected to high electrical tensions while being heated hot enough to overtake their work functions.This principle has led to the great success of the so-called vacuum tubes in the early 20 th century.To date,major challenges still remain in the miniaturization of a vacuum channel transistor for on-chip integration in modern solid-state integrated circuits.Here,by introducing nano-sized vacuum gaps(~200 nm)in a van der Waals heterostructure,we successfully fabricated a one-dimensional(1 D)edge-to-edge thermionic emission vacuum tube using graphene as the filament.With the increasing collector voltage,the emitted current exhibits a typical rectifying behavior,with the maximum emission current reaching 200 p A and an ON-OFF ratio of 10;.In addition,it is found that the maximum emission current is proportional to the number of the layers of graphene.Our results expand the research of nano-sized vacuum tubes to an unexplored physical limit of 1 D edge-to-edge emission,and hold great promise for future nano-electronic systems based on it.

Rational Design of Star-shaped Molecules with Benzene Core and Naphthalimide Derivatives End Groups as Organic Light-emitting Materials

A series of star-shaped molecules with benzene core and naphthalimides derivatives end groups have been designed to explore their optical,electronic,and charge transport properties as charge transport and/or luminescent materials for organic light-emitting diodes（OLEDs）. The frontier molecular orbitals（FMOs） analysis has turned out that the vertical electronic transitions of absorption and emission are characterized as intramolecular charge transfer（ICT）. The calculated results show that the optical and electronic properties of star-shaped molecules are affected by the substituent groups in N-position of 1,8-naphthalimide ring. Our results suggest that star-shaped molecules with n-butyl（1）,benzene（2）,thiophene（3）,thiophene S？,S？-dioxide（4）,benzo[c][1,2,5]thiadiazole（5）,and 2,7a-dihydrobenzo[d]thiazole（6） fragments are expected to be promising candidates for luminescent and electron transport materials for OLEDs. This study should be helpful in further theoretical investigations on such kind of systems and also to the experimental study for charge transport and/or luminescent materials for OLEDs.

Charge transporting materials for perovskite solar cells

Perovskite solar cells(PSCs) have made great progress since 2009 and become the focus of current research. As an important part of PSCs, charge transporting materials play an important role in the performance of the devices. In this review, we introduce the evolution of electron and hole transporting materials in PSCs in recent years and summarize some typical charge transporting materials and their applications in PSCs. For electron transporting materials, metal oxides(TiO_(2), SnO_(2) and ZnO) and organic materials(fullerenes, non-fullerenes and their derivatives)are the most widely used materials in PSCs. For hole transporting materials, small molecule spiro-OMeTAD(2,2’,7,7’-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9’-spirobifluorene), polymer PEDOT:PSS(poly(3,4-ethylenedioxythiophene): polystyrene sulfonate), PTAA(poly-[bi(4-phenyl)](2,4,3-trimethylphenyla-mine)), P3 HT(poly(3-hexythiophene)) and inorganic materials(NiOx, CuSCN, CuO) are adopted in PSCs. Finally, different types of charge transporting materials are summarized and their future development is prospected.

High efficiency ETM-free perovskite cell composed of CuSCN and increasing gradient CH_(3)NH_(3)PbI_(3)

To enhance device performance and reduce fabrication cost,a series of electron transporting material(ETM)-free perovskite solar cells(PSCs)is developed by TCAD Atlas.The accuracy of the physical mode of PSCs is verified,due to the simulations of PEDOT:PSS-CH_(3)NH_(3)PbI_(3)-PCBM and CuSCN-CH_(3)NH_(3)PbI_(3)-PCBM p-i-n PSCs showing a good agreement with experimental results.Different hole transporting materials(HTMs)are selected and directly combined with n-CH_(3)NH_(3)PbI_(3),and the CuSCN-CH_(3)NH_(3)PbI_(3) is the best in these ETM-free PSCs.To further study the CuSCN-CH_(3)NH_(3)PbI_(3) PSC,the influences of back electrode material,gradient band gap,thickness,doping concentration,and bulk defect density on the performance are investigated.Energy band and distribution of electric field are utilized to optimize the design.As a result,the efficiency of CuSCN-CH_(3)NH_(3)PbI_(3) PSC is achieved to be 26.64%.This study provides the guideline for designing and improving the performances of ETM-free PSCs.

High performance perovskite solar cells using TiO2 nanospindles as ultrathin mesoporous layer

Single crystal anatase TiO2 nanospindles （NSs） with highly exposed {101} facets were synthesized and employed as electron transport materials （ETMs） in perovskite solar cells （PSCs）. Time-resolved photoluminescence （TRPL） spectra revealed that the TiO2 NSs are more effective than TiO2 nanoparticles in accepting electrons from perovskite. Moreover. the TiO2 nanospindles further endowed the PSCs with good reproducibility and suppressed hysteresis. The best device with TiO2 NSs as ETMs yielded power conversion efficiency （PCE） of 19.6%, demonstrating that the home-made TiO2 NSs is a good ETM for PSCs.

A facile solution processed ZnO@ZnS core–shell nanorods arrays for high-efficiency perovskite solar cells with boosted stability

Zinc Oxide(ZnO)has been extensively applied as electron transport material(ETM)in perovskite solar cells(PSCs)since the emergence of PSCs.However,some chemisorbed oxygen species on the surface of ZnO can cause the degradation of CH3NH3+(MA^(+))based perovskite.To avoid the destructive effect of ZnO,a facile solution strategy was proposed to produce a ZnS shell around the ZnO nanorods arrays(ZnO-NRs),i.e.ZnO@ZnS core-shell nanorods(ZnO-NRs@ZnS).The ZnO-NRs@ZnS cascade structure can not only facilitate carrier transport,but also enhance the stability of ZnO based PSCs.A power conversion efficiency(PCE)of 20.6%was finally yielded,which is the-state-of-the-art efficiency for PSCs with one-dimensional(1 D)ZnO electron transport materials(ETMs).Moreover,over 90%of the initial efficiency was retained for the unencapsulated device with ZnO-NRs@ZnS ETMs at 85℃for 500 h,demonstrating excellent stability.This work provides a simple and efficient avenue to simultaneously enhance the photovoltaic(PV)performance and stability of 1 D ZnO nanostructure-based PSCs.

Appending triphenyltriazine to 1,10-phenanthroline: a robust electron-transport material for stable organic light-emitting diodes

There has been an increasing demand for high-performance and cost-effective organic electron-transport materials for organic light-emitting diodes （OLEDs）. In this contribution, we present a simple compound 3-（3-（4,6-diphenyl-l,3,5-triazin-2-yl）phenyl）-1,10-phenanthroline through the facile Pd-catalyzed coupling of a triphenyltriazine boronic ester with 3-hromo-1,10-phenanthroline. It shows a high Tg of 112℃. The ultraviolet photoelectron spectroscopy measurements reveal a deep HOMO level of -6.5 eV. The LUMO level is derived as -3.0 eV, based on the optical bandgap. The low-temperature solid-state phosphorescent spectrum gives a triplet energy of -2.36eV. n-Doping with 8-hydroxyquinolatolithium （Liq, 1：1） leads to considerably improved electron mobility of 5.2 × 10 -6 -5.8 × 10 -5 cm2 v-1 S-1 at E=（2-5） × 10 5Vcm -1, in contrast with the triarylphosphine oxide- phenantroline molecular conjugate we reported previously. It has been shown that through optimizing the device structure and hence suppressing polaron-exciton annihilation, introducing this single Liq-doped electron-transport layer could offer high-efficiency and stable phosphorescent OLEDs.

Recent progress in perovskite solar cells:material science

Perovskite solar cells represent a promising third-generation photovoltaic technology with low fabrication cost and high power conversion efficiency.In light of the rapid development of perovskite materials and devices,a systematic survey on the latest advancements covering a broad range of related work is urgently needed.This review summarizes the recent major advances in the research of perovskite solar cells from a material science perspective.The discussed topics include the devices based on different type of perovskites(organic-inorganic hybrid,all-inorganic,and lead-free perovskite and perovskite quantum dots),the properties of perovskite defects,different type of charge transport materials(organic,polymeric,and inorganic hole transport materials and inorganic and organic electron transport materials),counter electrodes,and interfacial materials used to improve the efficiency and stability of devices.Most discussions focus on the key progresses reported within the recent five years.Meanwhile,the major issues limiting the production of perovskite solar cells and the prospects for the future development of related materials are discussed.

Accelerating electron transport in Eosin Y by bidentately bridging on BaSnO_(3)for noble-metal-free photocatalytic H 2 production

The separation and transport of photogenerated carriers is regarded as a curial factor in photocatalytic H_(2)pro-duction.As known in solar cells and photoelectron-chemistry,to strengthen the electron conduction for effective utilization of carriers,the electron transport material(ETM)is widely applied.Herein,inspired by the function of ETM,we adopted barium stannate(BaSnO_(3),labeled as BSO)as an excellent ETM which had the merits of high electron mobility,suitable conduction band position and simple preparation,to adjust the carrier kinetics of dye Eosin Y(EY)-sensitized photocatalytic system.Detailly,the photocatalytic system with the spatial sepa-ration sites of photogenerated carriers excitation and water reduction reaction was elaborately constructed,that was,dye EY-sensitized BSO(EY/BSO)for photocatalytic H_(2)production.The photocatalytic H_(2)-production rate of EY/BSO(257𝜇mol·h^(−1)·g EY^(−1))in the absence of noble metals was 28.6 times higher than that of single EY(∼9𝜇mol·h^(−1)·g EY^(−1))under visible-light irradiation.With systematic and comprehensive characterizations,the formed electron transport channel by the bidentate bridging of EY on BSO could accelerate the transfer of photogenerated electrons from EY to BSO,promoting the effective separation of photogenerated carriers for the enhanced pho-tocatalytic performance.Moreover,the water reduction reaction for H_(2)production proceeded on the surface of BSO that acted as the H_(2)-evolution cocatalyst,avoiding the use of high-cost noble metals.Furthermore,based on the well-proved ETM-based concept in the EY/BSO system,La-doped BaSnO_(3)(LBSO)with better electron trans-port ability was adopted to construct EY/LBSO system(344𝜇mol·h^(−1)·g EY^(−1))which showed better photocatalytic activity than EY/BSO.

Recyclable Perovskite Solar Cells with Lead Sulfate Contact

Previous cost analysis of perovskite solar cells(PSCs)has revealed that the transparent conductive oxide(TCO)substrates account for most of the material cost,emphasizing the need to recover TCO in PSC recycling.However,the conventional use of compact and ultrathin electron transport materials(ETMs)such as TiO_(2)and SnO_(2),poses a challenge to their removal from the substrate,hindering effective PSC recycling.Here,PbSO_(4) nanoparticles with(011)surface were used as ETM to fabricate PSCs.The yielded metallicity on the PbSO_(4) nanoparticle surface promoted extracted electron transport across the nanoparticle surface.A certified efficiency as high as 17.9%for the submodule(204.9 cm^(2))with PbSO_(4) was realized successfully,and the best effi-ciency on a small area(0.1 cm^(2))reached 24.1%.The PbSO_(4) layer was removed effortlessly from the substrate by simple aminoethanol washing to recover the TCO,the most expensive component of PSCs.This work provides a novel strategy to prepare soluble insulator-based ETMs by constructing metallic surfaces of nanoparticles;thus,fabricating efficient and recyclable PSCs.

Interface materials for perovskite solar cells

Perovskite solar cells exhibit great potential to become commercial photovoltaic technology due to their high power conversion efficiency,low cost,solution processability,and facile large-area device manufacture.Interface engineering plays a significant role to optimize device performance.For the anode in the inverted devices,this review introduces the progress on the modification of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)including chemical structure alteration,physical doping,and solution treatment.We present the recent advances of dopant-free hole transport materials widely applied in mesoporous and conventional devices,outlining their innovation with novel molecular design concepts toward promising material properties,and device performance.For the cathode,various metal oxide and organic electron transport materials are covered and the different modification strategies and related mechanisms are highlighted.Most importantly,simple synthesis process,inexpensive raw materials and highly reproducible photovoltaic performance are the main consideration for the design of all the interface materials.Finally,an outlook and some suggestions regarding the future interface engineering are proposed based on the summary of the current development status and working mechanism of interface materials.

Synthesis and optoelectronic properties of amino-functionalized carbazole-based conjugated polymers

A series of alcohol soluble amino-functionalized carbazole-based copolymers were synthesized via Suzuki coupling reaction. The pendent amino groups endow them high solubility in polar solvents, as well as efficient electron injection capability from high work-function metals. The relationships between the photophysical and electrochemical properties and the polymer backbone structure were systematically investigated. These alcohol-soluble carbazole-based copolymers were used as cathode interlayers between the high work-function metal A1 cathode and P-PPV emissive layer in polymer light-emitting diodes with device structure of ITO/PEDOT：PSS/P-PPV/interlayer/A1. The resulting devices exhibited improved performance due to the better electron injection/transporting ability of the designed copolymers from A1 cathode to the light-emitting layer.

N-type metal-oxide electron transport layer for mesoscopic perovskite solar cells

To meet the challenge of continuously increasing global energy demands,organic-inorganic halide based perovskite solar cells(PSCs) have garnered great attention from the photovoltaic research community for their low cost and high efficiency.The efficiency of perovskite-based mesoscopic solar cells increases rapidly,from 3.8%in 2009 to22.1%in 2016.N-type metal-oxide electron transport layer,as one of the important components in mesoscopic PSCs(MPSCs),acts as not only a scaffold layer for the growth of perovskite crystals,but also a layer to supply transfer pathways for electrons injected from perovskites.In this review,we discussed recent published reports of MPSCs with the focus on n-type metal-oxide electron transport layer in MPSCs.The scaffold materials,scaffold nanostructure,and scaffold/perovskite interface engineering are considered,and the effects of these modifications of scaffolds on the performance of MPSCs are summarized in this review.

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.