Isomer Effects of Fullerene Derivatives on Organic Photovoltaics and Perovskite Solar Cells

Organic Solar Cells Based on Non-Fullerene Low Molecular Weight Organic Semiconductor Molecules

The development of narrow bandgap A-D-A- and ADA'DA-type non-fullerene small molecule acceptors (NFSMAs) along with small molecule donors (SMDs) have led to significant progress in all-small molecule organic solar cells. Remarkable power conversion efficiencies, nearing the range of 17-18 %, have been realized. These efficiency values are on par with those achieved in OSCs based on polymeric donors. The commercial application of organic photovoltaic technology requires the design of more efficient organic conjugated small molecule donors and acceptors. In recent years the precise tuning of optoelectronic properties in small molecule donors and acceptors has attracted considerable attention and has contributed greatly to the advancement of all-SM-OSCs. Several reviews have been published in this field, but the focus of this review concerns the advances in research on OSCs using SMDs and NFSMAs from 2018 to the present. The review covers the progress made in binary and ternary OSCs, the effects of solid additives on the performance of all-SM-OSCs, and the recently developed layer-by-layer deposition method for these OSCs. Finally, we present our perspectives and a concise outlook on further advances in all-SM-OSCs for their commercial application.

Unexpected and divergent mechanosynthesis of furanoid-bridged fullerene dimers C120O and C120O2

An unexpected, divergent and efficient approach toward furanoid-bridged fullerene dimers C120O and C120O2 was established under different solvent-free ball-milling conditions by simply using pristine C60 as the starting material, water as the oxygen source and FeCl3 as the mediator. The structures of C120O and C120O2 were unambiguously established by single-crystal X-ray crystallography. A plausible reaction mechanism is proposed on the basis of control experiments. Furthermore, C120O2 has been applied in organic solar cells as the third component and exhibits good performance.

25.71 %-Efficiency FACsPbI3 Perovskite Solar Cells Enabled by A Thiourea-based Isomer

Various isomers have been developed to regulate the morphology and reduce defects in state-of-the-art perovskite solar cells (PSCs). To insight the structure-function-effect correlations for the isomerization of thiourea derivatives on the performance of the PSCs, we developed two thiourea derivatives [(3,5-dichlorophenyl)amino]thiourea (AT) and N-(3,5-dichlorophenyl)hydrazinecarbothioamide (HB). Supported by experimental and calculated results, it was found that AT can bind with undercoordinated Pb2+ defect through synergistic interaction between N1 and C=S group with a defect formation energy of 1.818 eV, which is much higher than that from the synergistic interaction between two -NH- groups in HB and perovskite (1.015 eV). Moreover, the stronger interaction between AT and Pb2+ regulates the crystallization process of perovskite film to obtain a high-quality perovskite film with high crystallinity, large grain size, and low defect density. Consequently, the AT-treated FACsPbI3 device engenders an efficiency of 25.71 % (certified as 24.66 %), which is greatly higher than control (23.74 %) and HB-treated FACsPbI3 devices (25.05 %). The resultant device exhibits a remarkable stability for maintaining 91.0 % and 95.2 % of its initial efficiency after aging 2000 h in air condition or tracking at maximum power point for 1000 h, respectively.

Synthesis of [60]Fullerene-Fused Lactones via Carboxylic Acid Group-Directed C-H Bond Activation and Further Retro Baeyer-Villiger Reaction

An efficient palladium-catalyzed reaction of [60]fullerene with benzoic acids via carboxylic acid group-directed C-H bond activation is achieved. The obtained [60]fullerene-fused lactones can undergo a retro Baeyer-Villiger reaction to provide [60]fullerene-fused ketones via apparent reduction in the presence of triflic acid. A representative ketone product obtained by the reduction reaction can be employed as an overcoating layer for the electron-transporting layer in an n-type perovskite solar cell.

Catalytic System-Controlled Regioselective 1,2- and 1,4-Carboannulations of [60]Fullerene

Selective functionalization of fullerenes is an important but challenging topic in fullerene chemistry and synthetic chemistry. Here we present the first example of catalytic system-controlled regioselective 1,2- and 1,4-addition reactions for the flexible and efficient synthesis of novel 1,2- and 1,4-carbocycle-fused fullerenes via a palladium-catalyzed decarboxylative carboannulation process.

Regioswitchable Bingel Bis-Functionalization of Fullerene C70 via Supramolecular Masks

Isomer-pure functionalized fullerenes are required to boost the development of fullerene chemistry in any field, but their multiple functionalization renders a mixture of regioisomers that are very difficult to purify by chromatography. For the specific case of C70, its nonspherical geometry makes its regioselective functionalization more challenging than that of spherical C60. In this work, the supramolecular mask approach is applied for the first time to C70, which is encapsulated in two different nanocapsules to achieve the Bingel bis-cyclopropanation at α-bonds of opposite poles. Based on the tetragonal prismatic geometry imposed by the smaller supramolecular mask tested, the obtained major bis-adduct is completely reversed (major 5 o'clock) compared to bare C70 functionalization (major 2 o'clock). Moreover, by further restricting the accessibility of C70 using a three-shell Matryoshka mask and dibenzyl-bromomalonate, a single regiospecific 2 o'clock bis-isomer is obtained, owing to the perfect complementarity of the mask and the addend steric properties. The outcome of the reactions is fully explained at the molecular level by means of a thorough molecular dynamics (MD) study of the accessibility of the α-bonds to produce the different bis-adducts.

An open-cage bis[60]fulleroid as an electron transport material for tin halide perovskite solar cells

An open-cage bis[60]fulleroid (OC) was applied as an electron transport material (ETM) in tin (Sn) halide perovskite solar cells (PSCs). Due to the reduced offset between the energy levels of Sn-based perovskites and ETMs, the power conversion efficiency (PCE) of Sn-based PSCs with OC reached 9.6% with an open-circuit voltage (VOC) of 0.72 V. Additionally, OC exhibited superior thermal stability and provided 75% of the material without decomposition after vacuum deposition. The PSC using vacuum-deposited OC as the ETM could afford a PCE of 7.6%, which is a big leap forward compared with previous results using vacuum-deposited fullerene derivatives as ETMs.

Efficient Tin-Based Perovskite Solar Cells Enabled by Precisely Synthesized Single-Isomer Fullerene Bisadducts with Regulated Molecular Packing

Designing and synthesizing fullerene bisadducts with a higher-lying conduction band minimum is promising to further improve the device performance of tin-based perovskite solar cells (TPSCs). However, the commonly obtained fullerene bisadduct products are isomeric mixtures and require complicated separation. Moreover, the isomeric mixtures are prone to resulting in energy alignment disorders, interfacial charge loss, and limited device performance improvement. Herein, we synthesized single-isomer C60- and C70-based diethylmalonate functionalized bisadducts (C60BB and C70BB) by utilizing the steric-hindrance-assisted strategy and determined all molecular structures involved by single crystal diffraction. Meanwhile, we found that the different solvents used for processing the fullerene bisadducts can effectively regulate the molecular packing in their films. The dense and amorphous fullerene bisadduct films prepared by using anisole exhibited the highest electron mobility. Finally, C60BB- and C70BB-based TPSCs showed impressive efficiencies up to 14.51 and 14.28%, respectively. These devices also exhibited excellent long-term stability. This work highlights the importance of developing strategies to synthesize single-isomer fullerene bisadducts and regulate their molecular packing to improve TPSCs' performance.

Structure-Property Relationships for the Electronic Applications of Bis-Adduct Isomers of Phenyl-C61 Butyric Acid Methyl Ester

Higher adducts of a fullerene, such as the bis-adduct of PCBM (bis-PCBM), can be used to achieve shallower molecular orbital energy levels than, for example, PCBM or C60. Substituting the bis-adduct for the parent fullerene is useful to increase the open-circuit voltage of organic solar cells or achieve better energy alignment as electron transport layers in, for example, perovskite solar cells. However, bis-PCBM is usually synthesized as a mixture of structural isomers, which can lead to both energetic and morphological disorder, negatively affecting device performance. Here, we present a comprehensive study on the molecular properties of 19 pure bis-isomers of PCBM using a variety of characterization methods, including ultraviolet photoelectron spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, single crystal structure, and (time-dependent) density functional theory calculation. We find that the lowest unoccupied molecular orbital of such bis-isomers can be tuned to be up to 170 meV shallower than PCBM and up to 100 meV shallower than the mixture of unseparated isomers. The isolated bis-isomers also show an electron mobility in organic field-effect transistors of up to 4.5 × 10-2 cm2/(V s), which is an order of magnitude higher than that of the mixture of bis-isomers. These properties enable the fabrication of the highest performing bis-PCBM organic solar cell to date, with the best device showing a power conversion efficiency of 7.2%. Interestingly, we find that the crystallinity of bis-isomers correlates negatively with electron mobility and organic solar cell device performance, which we relate to their molecular symmetry, with a lower symmetry leading to more amorphous bis-isomers, less energetic disorder, and higher dimensional electron transport. This work demonstrates the potential of side chain engineering for optimizing the performance of fullerene-based organic electronic devices.

Scalable Solution-Processed Hybrid Electron Transport Layers for Efficient All-Perovskite Tandem Solar Modules

All-perovskite tandem solar cells offer the potential to surpass the Shockley-Queisser (SQ) limit efficiency of single-junction solar cells while maintaining the advantages of low-cost and high-productivity solution processing. However, scalable solution processing of electron transport layer (ETL) in p-i-n structured perovskite solar subcells remains challenging due to the rough perovskite film surface and energy level mismatch between ETL and perovskites. Here, scalable solution processing of hybrid fullerenes (HF) with blade-coating on both wide-bandgap (≈1.80 eV) and narrow-bandgap (≈1.25 eV) perovskite films in all-perovskite tandem solar modules is developed. The HF, comprising a mixture of fullerene (C60 ), phenyl C61 butyric acid methyl ester, and indene-C60 bisadduct, exhibits improved conductivity, superior energy level alignment with both wide- and narrow-bandgap perovskites, and reduced interfacial nonradiative recombination when compared to the conventional thermal-evaporated C60 . With scalable solution-processed HF as the ETLs, the all-perovskite tandem solar modules achieve a champion power conversion efficiency of 23.3% (aperture area = 20.25 cm2 ). This study paves the way to all-solution processing of low-cost and high-efficiency all-perovskite tandem solar modules in the future.

Exploring the Electronic, Optical, and Charge Transfer Properties of A-D-A-Type IDTV-ThIC-Based Molecules To Enhance Photovoltaic Performance of Organic Solar Cells

Improving the charge mobility and optoelectronic properties of indacenodithiophene-based small molecule acceptors is a key challenge to improving overall efficiency. In this current research, seven newly designed molecules (DT1-DT7) comprising the indacenodithiophene-based core are presented to tune energy levels, enhance charge mobility, and improve the photovoltaic performance of IDTV-ThIC molecules via density functional theory. All the molecules were designed by end-capped modification by substituting terminal acceptors of IDTV-ThIC with strong electron-withdrawing moieties. Among all the examined structures, DT1 has proved itself a superior molecule in multiple aspects, including higher λmax in chloroform (787 nm) and gaseous phase (727 nm), narrow band gap (2.16 eV), higher electron affinity (3.31 eV), least excitation energy (1.57 eV), and improved charge mobility due to low reorganization energy and higher excited state lifetime (2.37 ns) when compared to the reference (IDTV-ThIC) and other molecules. DT5 also showed remarkable improvement in different parameters, such as the lowest exciton binding energy (0.41 eV), leading to easier charge moveability. The improved open-circuit voltage of DT4 and DT5 makes them proficient molecules exhibiting the charge transfer phenomenon. The enlightened outcomes of these molecules can pave a new route to develop efficient organic solar cell devices using these molecules, especially DT1, DT4, and DT5.

Electrosynthesis of buckyballs with fused-ring systems from PCBM and its analogue

[6,6]-Phenyl-C61-butyric acid methyl ester (PCBM), a star molecule in the fullerene field, has found wide applications in materials science. Herein, electrosynthesis of buckyballs with fused-ring systems has been achieved through radical α-C-H functionalization of the side-chain ester for both PCBM and its analogue, [6,6]-phenyl-C61-propionic acid methyl ester (PCPM), in the presence of a trace amount of oxygen. Two classes of buckyballs with fused bi- and tricyclic carbocycles have been electrochemically synthesized. Furthermore, an unknown type of a bisfulleroid with two tethered [6,6]-open orifices can also be efficiently generated from PCPM. All three types of products have been confirmed by single-crystal X-ray crystallography. A representative intramolecularly annulated isomer of PCBM has been applied as an additive to inverted planar perovskite solar cells and boosted a significant enhancement of power conversion efficiency from 15.83% to 17.67%.

Dearomative Ring-Fused Azafulleroids and Carbazole-Derived Metallofullerenes: Reactivity Dictated by Encapsulation in a Fullerene Cage

Herein, we report divergent additions of 2,2'-diazidobiphenyls to C60 and Sc3 N@Ih -C80 . In stark contrast to that of the previously reported bis-azide additions, the unexpected cascade reaction leads to the dearomative formation of azafulleroids 2 fused with a 7-6-5-membered ring system in the case of C60 . In contrast, the corresponding reaction with Sc3 N@Ih -C80 switches to the C-H insertion pathway, thereby resulting in multiple isomers, including a carbazole-derived [6,6]-azametallofulleroid 3 and a [5,6]-azametallofulleroid 4 and an unusual 1,2,3,6-tetrahydropyrrolo[3,2-c]carbazole-derived metallofullerene 5, whose molecular structures have been unambiguously determined by single-crystal X-ray diffraction analyses. Among them, the addition type of 5 is observed for the first time in all reported additions of azides to fullerenes. Furthermore, unexpected isomerizations from 3 to 5 and from 4 to 5 have been discovered, providing the first examples of the isomerization of an azafulleroid to a carbazole-derived fullerene rather than an aziridinofullerene. In particular, the isomerism of the [5,6]-isomer 4 to the [5,6]-isomer 5 is unprecedented in fullerene chemistry, contradicting the present understanding that isomerization generally occurs between [5,6]- and [6,6]-isomers. Control experiments have been carried out to rationalize the reaction mechanism. Furthermore, representative azafulleroids have been applied in organic solar cells, thereby resulting in improved power conversion efficiencies.

An emissive charge-transfer excited-state at the well-defined hetero-nanostructure interface of an organic conjugated molecule and two-dimensional inorganic nanosheet

Precise engineering of excited-state interactions between an organic conjugated molecule and a two-dimensional semiconducting inorganic nanosheet, specifically the manipulation of charge-transfer excited (CTE) states, still remains a challenge for state-of-the-art photochemistry. Herein, we report a long-lived, highly emissive CTE state at structurally well-defined hetero-nanostructure interfaces of photoactive pyrene and two-dimensional MoS2 nanosheets via an N-benzylsuccinimide bridge (Py-Bn-MoS2). Spectroscopic measurements reveal that no charge-transfer state is formed in the ground state, but the locally-excited (LE) state of pyrene in Py-Bn-MoS2 efficiently generates an unusual emissive CTE state. Theoretical studies elucidate the interaction of MoS2 vacant orbitals with the pyrene LE state to form a CTE state that shows a distinct solvent dependence of the emission energy. This is the first example of organic-inorganic 2D hetero-nanostructures displaying mixed luminescence properties by an accurate design of the bridge structure, and therefore represents an important step in their applications for energy conversion and optoelectronic devices and sensors.

Synthesis of C60 /[10]CPP-Catenanes by Regioselective, Nanocapsule-Templated Bingel Bis-Addition

The addition of two unsymmetric malonate esters to the Buckminster fullerene C60 can lead to 22 spectroscopically distinguishable isomeric products and therefore represents a formidable synthesis challenge. In this work, we achieve 87 % selectivity for the formation of a single (in,out-trans-3) isomer by combining three approaches: (i) we use a starting material, in which the two malonates are covalently connected (tether approach); (ii) we form the strong supramolecular complex of C60 with the shape-persistent [10]CPP macrocycle (template approach) and (iii) we embed this complex further within a self-assembled nanocapsule (shadow mask approach). Variation of the spacer chain shed light on the limitations of the approach and the ring dynamics in the unusual [2]catenanes were studied in silico with atomistic resolution. This work significantly widens the scope of mechanically interlocked architectures comprising cycloparaphenylenes (CPP).

Copper-Mediated Radical-Induced Ring-Opening Relay Cascade Carboannulation Reaction of [60]Fullerene with Cyclobutanone Oxime Esters: Access to [60]Fullerene-Fused Cyclopentanes

An unexpected copper-mediated radical-induced ring-opening relay cascade carboannulation reaction of [60]fullerene with cyclobutanone oxime esters is presented for the preparation of various Cl-/Br-incorporated [60]fullerene-fused cyclopentanes. The unique relay cascade transformation uses inexpensive copper salts as promoters and halogen sources and features simple redox-neutral conditions and a broad substrate scope, providing a practical access to a class of novel five-membered carbocycle-fused fullerenes.

Transition-metal-mediated benzylation of C60 with benzyl chlorides

Benzyl bromides have been widely used for fullerene functionalization. However, the use of benzyl chlorides, a more affordable but less reactive counterpart of benzyl bromides, has been rarely reported. Herein, a new metal-mediated benzylation of C₆₀ with benzyl chlorides is presented. In this method, with the combinatorial use of Mn powder and Cu(OAc)₂, various benzyl chloride derivatives could react with C₆₀ to afford 1,4-dibenzylated products in 12-53% yields. A mechanistic study by in situ visible near infrared (vis-NIR) spectroscopy and various control experiments suggests that, unlike the conventional anionic pathway that uses benzyl bromides, the transition-metal-mediated benzylation of C₆₀ with benzyl chlorides proceeds via a metal-mediated iterative single electron transfer process.

Well-Defined Fullerene Bisadducts Enable High-Performance Tin-Based Perovskite Solar Cells

Tin-based perovskite solar cells (TPSCs) are attracting intense research interest due to their excellent optoelectric properties and eco-friendly features. To further improve the device performance, developing new fullerene derivatives as electron transporter layers (ETLs) is highly demanded. Four well-defined regioisomers (trans-2, trans-3, trans-4, and e) of diethylmalonate-C₆₀ bisadduct (DCBA) are isolated and well characterized. The well-defined molecular structure enables us to investigate the real structure-dependent effects on photovoltaic performance. It is found that the chemical structures of the regioisomers not only affect their energy levels, but also lead to significant differences in their molecular packings and interfacial contacts. As a result, the devices with trans-2, trans-3, trans-4, and e as ETLs yield efficiencies of 11.69%, 14.58%, 12.59%, and 10.55%, respectively, which are higher than that of the as-prepared DCBA-based (10.28%) device. Notably, the trans-3-based device also demonstrates a certified efficiency of 14.30%, representing one of the best-performing TPSCs.

[60]Fullerene-Fused Cyclopentanes: Mechanosynthesis and Photovoltaic Application

The mechanochemical cascade reaction of [60]fullerene with 3-benzylidene succinimides, diethyl 2-benzylidene succinate, or 2-benzylidene succinonitrile in the presence of an inorganic base has been investigated under solvent-free and ball-milling conditions. This protocol provides an expedient method to afford various [60]fullerene-fused cyclopentanes, showing advantages of good substrate scope, short reaction time, and solvent-free and ambient reaction conditions. Furthermore, representative fullerene products have been applied in inverted planar perovskite solar cells as efficient cathode interlayers.

Grape bunches of novel conjugated chain bonded fullerene oligomers: design of a potential electron trap carbonaceous molecular material

Developing π electron conjugated groups as covalent bonded bridges between fullerenes in their oligomers is key to optimizing and maximizing functions of the fullerene-based materials. In this work, a series of novel conjugated chain bonded fullerene C₆₀ oligomers (CBFOs) with a well-defined nano-architecture and "grape bunches" shapes are rationally designed and viably constructed based on fullerene-carbenes by means of DFT calculations. The results show that the presently designed CBFOs present a much better electron-accepting ability together with a much lower reorganization energy than the isolated fullerene C₆₀, and characterized as the potential ideal candidate for electron acceptors. The frontier molecular orbital and electron density analysis can well support the results of diabatic electron affinity (EA_a) and vertical electron affinity (EA_v) calculations. Moreover, these CBFOs exhibit strong absorption in the visible region but no obvious absorption in the ultraviolet region. In addition, the optical properties of the CBFOs and two dimensional structure are also simulated and explored theoretically. We hope that the present study would be helpful for developing covalent-bonded-fullerene based electron trap molecular materials, building blocks of nano-devices and nano-machinery applications.

Fluorinated Alcohol-Processed N-Type Organic Electrochemical Transistor with High Performance and Enhanced Stability

Tuning the film morphology and aggregated structure is a vital means to improve the performance of the mixed ionic-electronic conductors in organic electrochemical transistors (OECTs). Herein, three fluorinated alcohols (FAs), including 2,2,2-trifluoroethanol (TFE), 1,1,1,3,3,3-hexafluoroisopropanol (HFIP), and perfluoro-tert-butanol (PFTB), were employed as the alternative solvents for engineering the n-type small-molecule active layer gNR. Remarkedly, an impressive μC* of 5.12 F V^-1 cm^-1 s^-1 and a normalized transconductance of 1.216 S cm^-1 are achieved from the HFIP-fabricated gNR OECTs, which is three times higher than that of chloroform. The operational stability has been significantly enhanced by the FA-fabricated devices. Such enhancements can be ascribed to the aggregation-induced structural ordering by FAs during spin coating, which optimizes the microstructure of the films for a better mixed ion and electron transport. These results prove the huge research potential of FAs to improve OECT materials' processability, device performance, and stability, therefore promoting practical bio-applications.

Theoretical Study on the Diels–Alder Reaction of Fullerenes: Analysis of Isomerism, Aromaticity, and Solvation

Fullerenes are reactive as dienophiles in Diels–Alder reactions. Their distinctive molecular shape and properties result in interesting and sometimes elusive reaction patterns. Herein, to contribute to the understanding of fullerene reactivity, we evaluate the energies of reactions for Diels–Alder cycloadditions of C60, C70, and IC60MA with anthracene (Ant), by means of DFT computational analysis in vacuum and solution. The methods used showed little differentiation between the reactivity of the different fullerenes. The C70-Ant adducts where addition takes place near the edge of the fullerene were found to be the most stable regioisomers. For the IC60MA-Ant adducts, the calculated energies of reaction increase in the order: equatorial > trans-3 > trans-2 ≈ trans-4 ≈ trans-1 > cis-3 > cis-2. The change in the functional suggests the existence of stabilizing dispersive interactions between the surface of the fullerene and the addends. HOMA (harmonic oscillator model of aromaticity) analysis indicated an increase in aromaticity in the fullerene hexagons adjacent to the bonded addend. This increase is bigger in the rings of bisadduct isomers that are simultaneously adjacent to both addends, which helps explain the extra stability of the equatorial isomers. Solvation by m-xylene decreases the exothermicity of the reactions studied but has little distinguishing effect on the possible isomers. Thermal corrections reduce the exothermicity of the reactions by ~10 kJ∙mol−1.

Electrosynthesis of Decorated Basket Molecules: [60]Fullerene-Fused 12-Membered Macrolactones

The electrosynthesis of decorated basket molecules, that is, [60]fullerene-fused 12-membered macrolactones, has been achieved efficiently for the first time by the electrochemical reduction of [60]fullerene-fused 6-membered lactones and subsequent ring expansion with 1,2-bis(1-bromoalkyl)benzenes. The observed isomeric distributions of the obtained macrolactones are elucidated by theoretical calculations. The product structures have been firmly established by single-crystal X-ray analyses.

Electrochemically Promoted Benzylation of [60]Fullerooxazolidinone

Benzylation of the electrochemically generated dianion from N-p-tolyl-[60]fullerooxazolidinone with benzyl bromide provides three products with different addition patterns. The product distribution can be dramatically altered by varying the reaction conditions. Based on spectral characterizations, these products have been assigned as mono-benzylated 1,4-adduct and bis-benzylated 1,2,3,16- and 1,4,9,25-adducts, respectively. The assigned 1,2,3,16-adduct has been further established by X-ray diffraction analysis. It is believed that the 1,4-adduct is obtained by decarboxylative benzylation of the dianionic species, while bis-benzylated 1,2,3,16- and 1,4,9,25-adducts are achieved via a rearrangement process. In addition, the electrochemical properties of these products have been studied.

Transition-Metal-Free Domino Reaction of [60]Fullerene, Indole, and DMSO/HCl: One-Pot Access to Diverse N-Substituted [60]Fulleroindole Derivatives

An unprecedented multicomponent domino reaction of [60]fullerene, indole, and DMSO/HCl has been developed for the one-pot efficient synthesis of diverse N-substituted [60]fulleroindole derivatives. This methodology features simple operation, low cost, and transition-metal-circumvented and good functional group tolerance in indole.

Investigating the dielectric properties and exciton diffusion in C70 derivatives

In recent years, the dielectric constant (ε_r) of organic semiconductors (OSCs) has been of interest in the organic photovoltaic (OPV) community due to its potential influence on the exciton binding energy. Despite progress in the design of high ε_r OSCs and the accurate measurement of the ε_r, the effects of the synthetic strategies on specific (opto)electronic properties of the OSCs remain uncertain. In this contribution, the effects of ε_r on the optical properties of five new C₇₀ derivatives and [70]PCBM are investigated. Together with [70]PCBM, the derivatives have a range of ε_r values that depend on the polarity and length of the side chains. The properties of the singlet excitons are investigated in detail with steady-state and time-resolved spectroscopy and the exciton diffusion length is measured. All six derivatives show similar photophysical properties in the neat films. However, large differences in the crystallinity of the fullerene films influence the exciton dynamics in blend films. This work shows that design principles for OSCs with a higher ε_r can have a very different influence on the performance of traditional BHJ devices and in neat films and it is important to consider the neat film properties when investigating the optoelectronic properties of new materials for OPV.

Copper-mediated synthesis of fullerooxazoles from [60]fullerene and N-hydroxybenzimidoyl cyanides

A novel and efficient copper-mediated [3 + 2] heteroannulation reaction of [60]fullerene with N-hydroxybenzimidoyl cyanides has been developed for the synthesis of fullerooxazoles. A possible reaction mechanism involving unique C-CN and N-OH bond cleavages and subsequent C-OH bond formation for N-hydroxybenzimidoyl cyanides is proposed to explain the generation of fullerooxazoles. In addition, the formed fullerooxazoles can be further electrochemically transformed into amidated 1,2-hydrofullerenes.

Palladium-Catalyzed Three-Component 1,4-Alkoxyarylation Reaction of [60]Fullerene

The palladium-catalyzed three-component alkoxyarylation reaction of [60]fullerene with primary/secondary alcohols and aryl iodides generates a series of 1,4-(alkoxy)(aryl)[60]fullerene derivatives. Plausible reaction pathways for the formation of 1,4-(alkoxy)(aryl)[60]fullerenes are proposed. In addition, the electrochemical properties of the synthesized 1,4-alkoxyarylation adducts are investigated.

Photovoltaic Device Application of a Hydroquinone-Modified Conductive Polymer and Dual-Functional Molecular Si Surface Passivation Technology

In the last decades, the conductive polymer PEDOT:PSS has been introduced in Si-based hybrid solar cells, gaining noticeable research interest and being considered a promising candidate for next generation solar cells which can achieve both of low manufacturing cost and high power conversion efficiency. This study succeeded in improving the electrical conductivity of PEDOT:PSS to 937 S/cm through a simple process of adding hydroquinone (HQ) to the pristine PEDOT:PSS solution. The results also showed that the addition of HQ to PEDOT:PSS(HQ-PEDOT:PSS) could not only dramatically improve the conductivity but also well-sustain the work function characteristics of PEDOT:PSS by promoting the formation of more continuous conductive-PEDOT channels without removing the insulating PSS. In this report, we reveal that the application of the HQ-PEDOT:PSS to the Si/PEDOT:PSS HSC could significantly improve the short-circuit current and open-circuit voltage characteristics to increase the power conversion efficiency of the HSCs compared to the conventional approaches. Moreover, we also treated the Si surface with the organic monomer, benzoquinone (BQ) to (1) passivate the excess Si surface defect states and (2) to improve the properties of the Si/PEDOT:PSS interface. We show that BQ treatment is able to dramatically increase the minority carrier lifetime induced by effective chemical and field-effect passivation in addition to enhancing the wettability of the Si surface with the PEDOT:PSS solution. As a result, the power conversion efficiency was increased by 10.6% by introducing HQ and BQ into the fabrication process of the Si/PEDOT:PSS HSC.

Difluoromethylenation of fullerene C70 provides isomeric diversity and availability of equatorial [5,6]-homofullerene C70(CF2)

We report synthesis, isolation, and spectroscopic characterization of the novel [5,6]-open C70(CF2) isomer III along with the already known [6,6]-closed and [6,6]-open C70(CF2) isomers I and II. The compounds were...

Pyrazole-, isoxazole- and pyrrole-ring fused derivatives of C60: synthesis and electrochemical properties as well as morphological characterization

Pyrazole-, isoxazole- and pyrrole-ring fused derivatives of C60.

Palladium-catalyzed three-component 1,4-aminoarylation of [60]fullerene with aryl iodides and N-methoxysulfonamides, and further transformations

The palladium-catalyzed three-component 1,4-aminoarylation of [60]fullerene afforded 1,4-(aryl)(sulfonamide)[60]fullerenes, of which the sulfonamide group could be replaced by a (hetero)aryl, malonate ester or allyl group in the presence of FeCl3.

Unexpected Diels-Alder reaction of [60]fullerene with electron-deficient ferrocenes as cyclopentadiene surrogates

The unexpected Diels-Alder reaction of [60]fullerene (C₆₀) with ferrocenes bearing electron-withdrawing groups as cyclopentadiene surrogates has been developed to selectively afford single isomers of [2 + 4] cycloadducts of C₆₀. Mechanistic studies indicate that cyclopentadienes are in situ generated from electron-deficient ferrocenes in the presence of an oxidant and an acid, followed by [2 + 4] cycloadditions with dienophiles. A Michael addition reaction using a Grignard reagent has been utilized to transform the Diels-Alder adducts of C₆₀ into more stable fullerene derivatives.

Modelling of Stem Cells Microenvironment Using Carbon-Based Scaffold for Tissue Engineering Application-A Review

A scaffold is a crucial biological substitute designed to aid the treatment of damaged tissue caused by trauma and disease. Various scaffolds are developed with different materials, known as biomaterials, and have shown to be a potential tool to facilitate in vitro cell growth, proliferation, and differentiation. Among the materials studied, carbon materials are potential biomaterials that can be used to develop scaffolds for cell growth. Recently, many researchers have attempted to build a scaffold following the origin of the tissue cell by mimicking the pattern of their extracellular matrix (ECM). In addition, extensive studies were performed on the various parameters that could influence cell behaviour. Previous studies have shown that various factors should be considered in scaffold production, including the porosity, pore size, topography, mechanical properties, wettability, and electroconductivity, which are essential in facilitating cellular response on the scaffold. These interferential factors will help determine the appropriate architecture of the carbon-based scaffold, influencing stem cell (SC) response. Hence, this paper reviews the potential of carbon as a biomaterial for scaffold development. This paper also discusses several crucial factors that can influence the feasibility of the carbon-based scaffold architecture in supporting the efficacy and viability of SCs.

Isocyanide-Induced Annulation Leading to Cyclopento-, Methano-, and Cyclopentano-[60]Fullerene Derivatives

The three-component annulation reactions of C₆₀, alkyl isocyanide, and dimethyl acetylenedicarboxylate (DMAD) or unsymmetric alkynes are investigated to afford cyclopent-2-en-1-imino- and ketenimine methano-[60]fullerene derivatives, which, upon hydration in the presence of acid, yield the corresponding fullerene amides. Dimethyl 2,3-pentadienedioate, the allene counterpart of DMAD, and ethyl buta-2,3-dienoate undergo four-component annulation with C₆₀, alkyl isocyanide, and water under similar conditions to yield cyclopentano-[60]fullerene derivatives with similar amide groups.

Graphitic supramolecular architectures based on corannulene, fullerene, and beyond

In this Feature Article, we survey the advances made in the field of fulleretic materials over the last five years. Merging the intriguing characteristics of fulleretic molecules with hierarchical materials can lead to enhanced properties of the latter for applications in optoelectronic, biomaterial, and heterogeneous catalysis sectors. As there has been significant growth in the development of fullerene- and corannulene-containing materials, this article will focus on studies performed during the last five years exclusively, and highlight the recent trends in designing fulleretic compounds and understanding their properties, that has enriched the repertoire of carbon-rich functional materials.

Long-Lived C60 Radical Anion Stabilized Inside an Electron-Deficient Coordination Cage

Fullerene C₆₀ and its derivatives are widely used in molecular electronics, photovoltaics, and battery materials, because of their exceptional suitability as electron acceptors. In this context, single-electron transfer on C₆₀ generates the C₆₀^• - radical anion. However, the short lifetime of free C₆₀^• - hampers its investigation and application. In this work, we dramatically stabilize the usually short-lived C₆₀^• - species within a self-assembled M₂L₄ coordination cage consisting of a triptycene-based ligand and Pd(II) cations. The electron-deficient cage strongly binds C₆₀ by providing a curved inner π-surface complementary to the fullerene's globular shape. Cyclic voltammetry revealed a positive potential shift for the first reduction of encapsulated C₆₀, which is indicative of a strong interaction between confined C₆₀^• - and the cationic cage. Photochemical one-electron reduction with 1-benzyl-1,4-dihydronicotinamide allows selective and quantitative conversion of the confined C₆₀ molecule in millimolar acetonitrile solution at room temperature. Radical generation was confirmed by nuclear magnetic resonance, electron paramagnetic resonance, ultraviolet-visible-near-infrared spectroscopy and electrospray ionization mass spectrometry. The lifetime of C₆₀^• - within the cage was determined to be so large that it could still be detected after one month under an inert atmosphere.

Deep-red circularly polarised luminescent C70 derivatives

Optically active fullerenes, including C₆₀ and C₇₀ derivatives carrying organic substituents, are used in a range of applications because of their unique spectroscopic, catalytic, and chiral recognition properties. However, their inherent photoexcited chirality is yet to be elucidated because of their very poor fluorescence quantum yield (Φ_f). We synthesised a new chiral C₇₀ derivative, X70A, with 20% yield, by reacting bis-borylated xanthene with C₇₀ in a one-step double addition reaction, followed by a successful optical resolution. The isolation of two separate X70A enantiomers was confirmed by mirror-image circular dichroism spectroscopy in the range of 300–750 nm. In toluene, the enantiomeric pair of X70A clearly revealed mirror-image circularly polarised luminescence (CPL) spectra with a high |g_lum| value of 7.0 ×  10⁻³ at 690 nm. The first fullerene-based deep-red CPL of X70A should provide a new guideline for the design of chiral nanocarbon materials.

Cu(I)-Catalyzed Synthesis of [60]Fullerene-Fused Lactams and Further Electrochemical Functionalization

A novel and efficient Cu(I)-catalyzed radical heteroannulation reaction of [60]fullerene (C₆₀) with α-bromo acetamides has been disclosed for the direct synthesis of diverse C₆₀-fused lactams. Furthermore, the formed C₆₀-fused lactams can be served as a versatile platform for further electrochemical functionalization to prepare 1,2-, 1,4-, 1,2,3,16-, and 1,4,9,25-adducts of C₆₀. In addition, a representative fullerene product has been applied as an overcoating layer of the electron-transporting layer in n-type perovskite solar cell.

A three-shell supramolecular complex enables the symmetry-mismatched chemo- and regioselective bis-functionalization of C60

Molecular Russian dolls (matryoshkas) have proven useful for testing the limits of preparative supramolecular chemistry but applications of these architectures to problems in other fields are elusive. Here we report a three-shell, matryoshka-like complex-in which C₆₀ sits inside a cycloparaphenylene nanohoop, which in turn is encapsulated inside a self-assembled nanocapsule-that can be used to address a long-standing challenge in fullerene chemistry, namely the selective formation of a particular fullerene bis-adduct. Spectroscopic evidence indicates that the ternary complex is sufficiently stable in solution for the two outer shells to affect the addition chemistry of the fullerene guest. When the complex is subjected to Bingel cyclopropanation conditions, the exclusive formation of a single trans-3 fullerene bis-adduct was observed in a reaction that typically yields more than a dozen products. The selectivity facilitated by this matryoshka-like approach appears to be a general phenomenon and could be useful for applications where regioisomerically pure C₆₀ bis-adducts have been shown to have superior properties compared with isomer mixtures.