Recent advances in the synthesis of cyclic sulfinic acid derivatives (sultines and cyclic sulfinamides)

The chemistry of cyclic sulfinic acid derivatives (sultines and cyclic sulfinamides) was underdeveloped for a long time due to their inaccessibility. Considering the importance of cyclic sulfinate esters and amides in the fields of chemistry, pharmaceutical science, and material science, synthesis strategies involving cyclic sulfinic acid derivatives have been paid more attention in recent years, and have been widely used in the synthesis of sulfur-containing compounds such as sulfoxides, sulfones, sulfinates and thioethers. Despite the impressive improvements that have been made in last twenty years with the new strategies, to date, no reviews have been published, to the best of our knowledge, dealing with the preparation of cyclic sulfinic acid derivatives. This review summarizes the latest advances in the development of new synthesis methods to access cyclic sulfinic acid derivatives in the last two decades. The synthetic strategies are reviewed by highlighting their product diversity, selectivity and applicability, and the mechanistic rationale is presented where possible. We wish to bring readers a comprehensive understanding of the state-of-play of cyclic sulfinic acid derivative formation and make a contribution to future research.

In Silico Modeling of New "Y-Series"-Based Near-Infrared Sensitive Non-Fullerene Acceptors for Efficient Organic Solar Cells

This work was inspired by a previous report [Janjua, M. R. S. A. Inorg. Chem. 2012, 51, 11306-11314] in which the optoelectronic properties were improved with an acceptor bearing heteroaromatic rings. Herein, we have designed four novel Y-series non-fullerene acceptors (NFAs) by end-capped acceptor modifications of a recently synthesized 15% efficient Y21 molecule for better optoelectronic properties and their potential use in solar cell applications. Density functional theory (DFT) along with time-dependent density functional theory (TDDFT) at the B3LYP/6-31G(d,p) level of theory is used to calculate the band gap, exciton binding energy along with transition density matrix (TDM) analysis, reorganizational energy of electrons and holes, and absorption maxima and open-circuit voltage of investigated molecules. In addition, the PM6:YA1 complex is also studied to understand the charge shifting from the donor polymer PM6 to the NFA blend. Results of all parameters suggest that the DA'D electron-deficient core and effective end-capped acceptors in YA1-YA4 molecules form a perfect combination for effective tuning of optoelectronic properties by lowering frontier molecular orbital (FMO) energy levels, reorganization energy, and binding energy and increasing the absorption maximum and open-circuit voltage values in selected molecules (YA1-YA4). The combination of extended conjugation and excellent electron-withdrawing capability of the end-capped acceptor moiety in YA1 makes YA1 an excellent organic solar cell (OSC) candidate owing to promising photovoltaic properties including the lowest energy gap (1.924 eV), smallest electron mobility (λe = 0.0073 eV) and hole mobility (λh = 0.0083 eV), highest λmax values (783.36 nm (in gas) and 715.20 nm (in chloroform) with lowest transition energy values (E x) of 1.58 and 1.73 eV, respectively), and fine open-circuit voltage (V oc = 1.17 V) with respect to HOMOPM6-LUMOacceptor. Moreover, selected molecules are observed to have better photovoltaic properties than Y21, thus paving the way for experimentalists to look for future developments of Y-series-based highly efficient solar cells.

Thiophene- and Carbazole-Substituted N-Methyl-Fulleropyrrolidine Acceptors in PffBT4T-2OD Based Solar Cells

The impact of fullerene side chain functionalization with thiophene and carbazole groups on the device properties of bulk-heterojunction polymer:fullerene solar cells is discussed through a systematic investigation of material blends consisting of the conjugated polymer poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3‴-di(2-octyldodecyl)-2,2';5',2″;5″,2‴-quaterthiophen-5,5‴-diyl)] (PffBT4T-2OD) as donor and C60 or C70 fulleropyrrolidines as acceptors. The photovoltaic performance clearly depended on the molecular structure of the fulleropyrrolidine substituents although no direct correlation with the surface morphology of the photoactive layer, as determined by atomic force microscopy, could be established. Although some fulleropyrrolidines possess favorable lowest unoccupied molecular orbital levels, when compared to the standard PC71BM, they originated OPV cells with inferior efficiencies than PC71BM-based reference cells. Fulleropyrrolidines based on C60 produced, in general, better devices than those based on C70, and we attribute this observation to the detrimental effect of the structural and energetic disorder that is present in the regioisomer mixtures of C70-based fullerenes, but absent in the C60-based fullerenes. These results provide new additional knowledge on the effect of the fullerene functionalization on the efficiency of organic solar cells.

Efficient organic solar cells based on a new “Y-series” non-fullerene acceptor with an asymmetric electron-deficient-core

Herein, a new “Y-series” non-fullerene acceptor, Y21, bearing an asymmetric electron-deficient-core (DA′D) and fluorinated dicyanomethylene derivatives as flanking groups, was designed and synthesized for organic solar cell applications.

Improved efficiency and thermal stability of ternary all-small-molecule organic solar cells by NCBA as a third component material

In this work, organic solar cells (OSCs) were fabricated with a blend of PC₇₁BM and p-DTS-(FBTTh₂)₂ employed as a binary photoactive layer and with a dihydronaphthyl-based C60 bisadduct (NCBA) small-molecule acceptor used as a third component material. We demonstrate that the short-circuit current density (J_SC), open-circuit voltage (V_OC), fill factor (FF), power conversion efficiency (PCE), and thermal stability can all be enhanced simultaneously. In addition, the crystallinity can be finely optimized and the photon harvesting ability was enhanced for short-wavelength light by adjusting the NCBA doping ratio, leading to efficient exciton dissociation and charge-carrier transport. At the same time, the ternary photoactive layer, with a small amount of NCBA as a third component material, reduced monomolecular recombination and bimolecular recombination under open-circuit and short-circuit conditions, respectively. Such a ternary structure with NCBA as a third component material helped enhance the crystallinity and fix the surface morphology of the photoactive layer, thus reducing the decay ratio while increasing the thermal annealing treatment time. Consequently, the PCE reaches 9.1% for ternary OSCs with a 12 wt% NCBA doping ratio in a blended acceptor, with 87.2% of the initial PCE value maintained after 100 h of thermal annealing treatment at 90 °C, which is much higher than that obtained for the PCE of binary OSCs.

Effect of dihydronaphthyl-based C60 bisadduct as third component materials on the photovoltaic performance and charge carrier recombination of binary PBDB-T : ITIC polymer solar cells

A dihydronaphthyl-based C60 bisadduct (NCBA) acceptor was introduced as a third component to typical poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b0]dithiophene))-alt-(5,5-(10,30-di-2-thienyl-50,70-bis(2-ethylhexyl)benzo[10,20-c:40,50-c0]dithiophene-4,8-dione))] (PBDB-T): 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:20,30-d0]-s-indaceno[1,2-b:5,6-b0]-dithiophene (ITIC) binary polymer solar cells (PSCs). NCBA plays a bridging role between the lowest unoccupied molecular orbital (LUMO) of PBDB-T and ITIC and provides more routes for charge carrier transfer at the interface between PBDB-T and ITIC, whereupon a higher open-circuit voltage (VOC) could be realized upon the addition of NCBA relative to the neat ITIC as an electron acceptor. With the strong visible light absorption in the range from 300 to 520 nm of the NCBA molecule, it had the effect of apparently complementary visible light absorption compared with the binary PBDB-T : ITIC layer. The crystallinity and surface morphology of the PBDB-T : NCBA : ITIC (1 : 0.1 : 0.9) thin films was similar to that of the binary PBDB-T : ITIC layer, which guaranteed suitable efficient exciton dissociation and charge carrier transport. The photocurrent density versus effective voltage (Jph-Veff) curves, short-circuit current density (JSC), and VOC as a function of incident light intensity as well as the transient photovoltage (TPV) and transient photocurrent (TPC) were measured, and the results illustrated the effects of NCBA as third component materials in terms of efficient exciton dissociation and reduced charge carrier recombination and loss. The PBDB-T : NCBA : ITIC (1 : 0.1 : 0.9)-based PSCs showed an optimized PCE value of 9.56% and better thermal stability after 10 h thermal annealing treatment (the normalized PCE value was 92.5% of the initial PCE value).

Benzylic C(sp3)–H bond sulfonylation of 4-methylphenols with the insertion of sulfur dioxide under photocatalysis

Sulfonylation of the benzylic C–H bond is developed through a three-component reaction of aryldiazonium tetrafluoroborates, 4-methylphenols and sodium metabisulfite (Na₂S₂O₅). The inorganic sulfite of sodium metabisulfite is used as the SO₂ surrogate.

Interfacial Reaction of Fulleropyrrolidines Affecting Organic Photovoltaic Performance

Fulleropyrrolidine derivatives are intrinsically basic owing to the amino group within the pyrrolidine structure. It can be predicted that the basicity of fulleropyrrolidine may affect the photovoltaic devices containing an acidic layer (e.g.

, PEDOT

PSS). To clarify the effect of basic fulleropyrrolidine derivatives, we synthesized compounds with an N-benzyl substituent group and fabricated organic photovoltaic (OPV) cells using this N-benzyl fulleropyrrolidine. A device structure with the ITO/PEDOT:PSS/organic layer (PTB7:fulleropyrrolidine)/Ca/Al showed high series resistance, short-circuit current density (J_sc), and low fill factor (FF) values. However, OPV cells having an inverted structure, without the PEDOT:PSS layer, contributed good device performance. We were able to reproduce the high series resistance in a model experiment using aqueous ammonia vapor to treat the PEDOT:PSS layer. Our results indicated that the activity of the PEDOT:PSS layer was affected by the basicity of the fulleropyrrolidines. These results also explain why this phenomenon does not occur at the interface of OPV devices when conventional [6,6]-phenyl C₆₁ butyric acid methyl ester is used as an acceptor material. This finding would contribute to enhancing the OPV device performances from a chemical view point of designing a new compound.

Tuning reaction products by constrained optimisation

An effective means of defining optimisation criteria for self-optimising criteria is described, applicable to situations where a compromise is sought between several competing objectives.

Novel fullerene-based porous materials constructed by a solvent knitting strategy

Here we choose a dihydronaphthyl-functionalized C₆₀ fullerene as a building block and utilize a novel solvent knitting strategy based on Friedel–Crafts alkylation reaction to construct two kinds of novel porous materials by using dichloromethane (DCM) and 1,2-dichloroethane (DCE) as solvents and external crosslinkers.

Colloidal aggregation and structural assembly of aspect ratio variant goethite (α-FeOOH) with nC60 fullerene in environmental media

Environmental mobility of C₆₀ fullerene can be significantly affected in the presence of naturally abundant α-FeOOH. However, α-FeOOH vary significantly in sizes, shapes and associated properties that can greatly influence the fate and transport of C₆₀ fullerene in environmental media. Therefore, colloidal hetero-association between well crystallized low aspect (L_Asp) α-FeOOH and nC₆₀ fullerene may differ substantially to weakly crystallized high-aspect (H_Asp) counterpart. In contrast to L_Asp α-FeOOH, inherent crystal defects and surface charge generation in H_Asp α-FeOOH facilitated strong Coulombic attraction and aggregation with fullerene in acidic pH. However, L_Asp α-FeOOH demonstrated subtle entropic depletion mediated interaction with fullerene prevalent in hard rods. Humic acid (HA) encapsulation of H_Asp α-FeOOH substantially blocked fullerene attachment. Minute enhancement in colloidal stability was detected for HA-coated H_Asp α-FeOOH and fullerene mixture to HA-coated H_Asp α-FeOOH alone. To investigate the interfacial assembly of α-FeOOH with fullerene "in situ" differential interference contrast (DIC) microscopic investigations were employed. This study showed significantly different interface behavior of the binary mixtures of fullerene and H_Asp α-FeOOH NPs, and L_Asp particles. On air-water interface, bare H_Asp α-FeOOH displayed liquid crystalline packing. However, addition of fullerene to H_Asp α-FeOOH suspension at pH5 produced closed-loop polygonal and circular ring structures. Head-to-tail alignment of magnetic dipoles as well as fullerene hydrophobicity facilitated such assembly formation. "Ex situ" AFM investigation revealed further the presence of magnetically derived ring structure which asserts that the formed "in situ" ensembles were not transient, hence, may abate fullerene transport through environmental interfaces. Barring hydrophobicity assisted attachment of fullerene to L_Asp α-FeOOHs, the absence of any close-packed structures may unlikely abate fullerene transport as envisaged in case of H_Asp α-FeOOH. Thus, aspect ratio variation and associated material properties of naturally abundant α-FeOOH may significantly impact fullerene transport through environmental media.

Modified structure of two-dimensional polythiophene derivatives by incorporating electron-deficient units into terthiophene-vinylene conjugated side chains and the polymer backbone: synthesis, optoelectronic and self-assembly properties, and photovoltaic application

Molecular engineering on the conjugated side chains of two-dimensional (2D) conjugated polymers was conducted and its effect on the optical, electronic, self-assembly and photovoltaic properties was investigated.

Stability of organic solar cells: challenges and strategies

This review highlights the factors limiting the stability of organic solar cells and recent developments in strategies to increase the stability of organic solar cells.

Manganese powder promoted highly efficient and selective synthesis of fullerene mono- and biscycloadducts at room temperature

Discovery of an efficient, practical, and flexible synthetic method to produce various important electron acceptors for low-cost organic photovoltaics (OPVs) is highly desirable. Although the most commonly used acceptor materials, such as PC₆₁BM, PC₇₁BM, IC₆₀BA, bisPC₆₁BM have been proved to be promising for the OPVs, they are still very expensive mainly due to their low production yields and limited synthetic methods. Herein, we report an unprecedented and innovative synthetic method of a variety of fullerene mono- and biscycloadducts by using manganese powder as a promotor. The reaction of fullerenes with various dibromides proceeds efficiently and selectively under very mild conditions to give the corresponding cycloadducts in good to excellent yields. The combination of manganese power with DMSO additive is crucial for the successful implementation of the present cycloaddition. Notably, the standard OPV acceptors, such as PCBMs, have been obtained in extraordinarily high yields, which cannot be achieved under the previously reported methods.

Effects of alkyl chain length and substituent pattern of fullerene bis-adducts on film structures and photovoltaic properties of bulk heterojunction solar cells

A series of alkoxycarbonyl-substituted dihydronaphthyl-based [60]fullerene bis-adduct derivatives (denoted as C2BA, C4BA, and C6BA with the alkyl chain of ethyl, n-butyl, and n-hexyl, respectively) have been synthesized to investigate the effects of alkyl chain length and substituent pattern of fullerene bis-adducts on the film structures and photovoltaic properties of bulk heterojunction polymer solar cells. The shorter alkyl chain length caused lower solubility of the fullerene bis-adducts (C6BA > C4BA > C2BA), thereby resulting in the increased separation difficulty of respective bis-adduct isomers. The device performance based on poly(3-hexylthiophene) (P3HT) and the fullerene bis-adduct regioisomer mixtures was enhanced by shortening the alkyl chain length. When using the regioisomerically separated fullerene bis-adducts, the devices based on trans-2 and a mixture of trans-4 and e of C4BA exhibited the highest power conversion efficiencies of ca. 2.4%, which are considerably higher than those of the C6BA counterparts (ca. 1.4%) and the C4BA regioisomer mixture (1.10%). The film morphologies as well as electron mobilities of the P3HT:bis-adduct blend films were found to affect the photovoltaic properties considerably. These results reveal that the alkyl chain length and substituent pattern of fullerene bis-adducts significantly influence the photovoltaic properties as well as the film structures of bulk heterojunction solar cells.

Efficient polymer solar cells based on poly(3-hexylthiophene) and indene-C₆₀ bisadduct fabricated with non-halogenated solvents

The photovoltaic performance of poly(3-hexylthiophene) (P3HT) has been improved greatly by using indene-C60 bisadduct (ICBA) as acceptor instead of phenyl-C61-butyric acid methyl ester (PCBM). However, the solvent of dichlorobenzene (DCB) used in fabricating polymer solar cells (PSCs) limited the application of the PSCs, because of the environmental problem caused by the harmful halogenated solvent. In this work, we fabricated the PSCs based on P3HT/ICBA processed with four low-harmful non-halogenated solvents of toluene, o-xylene, m-xylene, and p-xylene. The PSCs based on P3HT/ICBA (1:1, w/w) with toluene as the solvent exhibit the optimized power conversion efficiency (PCE) of 4.5% with open-circuit voltage (Voc) of 0.84 V, short circuit current density (Jsc) of 7.2 mA/cm(2), and fill factor (FF) of 71%, under the illumination of AM 1.5G at 100 mW/cm(2). Upon using 1% N-methyl pyrrolidone (NMP) as a solvent additive in the toluene solvent, the PCE of the PSCs was greatly improved to 6.6% with a higher Jsc of 10.3 mA/cm(2) and a high FF of 75%, which is even higher than that of the devices fabricated with halogenated DCB solvent. The X-ray diffraction (XRD) measurement shows that the crystallinity of P3HT increased with the NMP additive. The investigations on morphology of the active layers by atomic force microscopy (AFM) and transmission electron microscopy (TEM) indicate that the NMP additive promotes effective phase separation and formation of nanoscaled interpenetrating network structure of the active layer, which is beneficial to the improvement of Jsc and PCE for the PSCs fabricated with toluene as the solvent.

Optoelectronic properties of a fullerene derivative containing adamantane group

A fullerene derivative linked with an adamantane cage, [6,6]-phenyl-C61-butyric acid 1-adamantane methyl ester (PC61BAd), has been designed and synthesized. Systematic investigations on its organic field effect performance, photovoltaic properties, and corresponding thermal stability have been made. In OFET device, the electron mobility (μe) of PC61BAd was found to reach a value as high as 0.01 cm(2)/V·s with a high on-off (Ion/Ioff) ratio of 4.9 × 10(6) that is useful for logic device applications. In the organic photovoltaic devices of P3HT:PC61BAd, the power conversion efficiency (PCE) was found to reach 3.31 % in the optimized device. More importantly, the active layer of P3HT:PC61BAd was found to exhibit superior thermal stability over that of P3HT:PC61BM. After heating at 150 °C for 20 h, the P3HT:PC61BAd device still showed a PCE of 2.44 %, demonstrating the applicability of PC61BAd as an acceptor material for the preparation of thermally stable organic solar cells. X-ray diffraction and atomic force microscopy were employed to probe the structure and morphology of PC61BAd and to rationalize its performance as an organic electronic material.

Fullerene-bisadduct acceptors for polymer solar cells

Polymer solar cells (PSCs) have drawn great attention in recent years for their simple device structure, light weight, and low-cost fabrication in comparison with inorganic semiconductor solar cells. However, the power-conversion efficiency (PCE) of PSCs needs to be increased for their future application. The key issue for improving the PCE of PSCs is the design and synthesis of high-efficiency conjugated polymer donors and fullerene acceptors for the photovoltaic materials. For the acceptor materials, several fullerene-bisadduct acceptors with high LUMO energy levels have demonstrated excellent photovoltaic performance in PSCs with P3HT as a donor. In this Focus Review, recent progress in high-efficiency fullerene-bisadduct acceptors is discussed, including the bisadduct of PCBM, indene-C60 bisadduct (ICBA), indene-C70 bisadduct (IC70BA), DMPCBA, NCBA, and bisTOQC. The LUMO levels and photovoltaic performance of these bisadduct acceptors with P3HT as a donor are summarized and compared. In addition, the applications of an ICBA acceptor in new device structures and with other conjugated polymer donors than P3HT are also introduced and discussed.

Efficient light trapping in inverted polymer solar cells by a randomly nanostructured electrode using monodispersed polymer nanoparticles

The randomly nanotextured back electrode provides a simple and efficient route for enhancing photocurrent in polymer solar cells (PSCs) by light trapping, which can increase light absorption within a finite thickness of the active layer. In this study, we incorporated mono-disperse 60 nm polystyrene nanoparticles (PS NPs) into a 50 nm thick poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) anode buffer layer (ABL) to create a randomly nanotextured back electrode with 10 nm height variations in inverted-type PSCs. The roughened interface between the PS NP-PEDOT:PSS ABL and the Ag electrode scatters light in the visible range, leading to efficient light trapping within the device and enhanced light absorption in the active layer. Inverted PSCs with randomly nanotextured electrodes (φ(NP) = 0.31) showed short-circuit current density (J(SC)) and power conversion efficiency (PCE) values that were 15% higher than those of control devices with flat electrodes. External quantum efficiency, reflectance, and optical light scattering as a function of ϕ(NP) were examined to determine the origin of the enhancement in J(SC) and PCE.

Synthesis of novel acceptor molecules of mono- and multiadduct fullerene derivatives for improving photovoltaic performance

We have successfully synthesized and separated a series of tert-butyl 4-C(61)-benzoate (t-BCB) organofullerenes, including monoadduct, diadduct, and triadduct compounds, and investigated their photophysics, electrochemistry, thermal properties, and high-performance liquid chromatography analysis. The photovoltaic devices were fabricated based on monoadduct, diadduct, and triadduct products, and the devices based on them exhibited power conversion efficiencies of 2.43%, 0.48%, and 1.68%, respectively. This was the first time to study the dependent relationship on the device performance and the different isomer numbers.

Effects of alkoxy chain length in alkoxy-substituted dihydronaphthyl-based [60]fullerene bisadduct acceptors on their photovoltaic properties

A series of alkoxy-substituted dihydronaphthyl-based [60]fullerene bisadduct derivatives (Cn-NCBA, n = 1-6), with the alkoxy chain length from 1 to 6 carbon atoms, were synthesized as acceptors for polymer solar cells (PSCs), for the purpose of systematically investigating the effects of fullerene derivative structures on the photovoltaic properties of PSCs. Although the absorption spectra and electrochemical properties of Cn-NCBA are almost the same, the PSCs based on P3HT:Cn-NCBA showed different photovoltaic properties. The device based on the P3HT:C3-NCBA blend demonstrated the highest power-conversion efficiency (PCE) of ca. 4.1%, while those with shorter or longer alkoxy-substituted dihydronaphthyl-based [60]fullerene bisadduct derivatives showed relatively lower PCE values. C5-NCBA and C6-NCBA with longer alkoxy chain length showed relatively low electron mobilities, leading to relatively poor photovoltaic performance. More importantly, we found that the alkoxy chain length changes the hydrophobicity of Cn-NCBA and, thus, the interfacial interaction and miscibility with P3HT, which were analyzed by interfacial tension and atomic force microscopy (AFM) measurements. The hydrophobicity of Cn-NCBA increased as the alkoxy chain length increased. A distinct phase separation for the P3HT:C1-NCBA blend film due to the large interfacial tension and poor miscibility between P3HT and C1-NCBA could be one reason for the low PCE value of the C1-NCBA-based devices. C3-NCBA may provide the most appropriate combination of electron mobility and miscibility with P3HT to achieve optimal photovoltaic properties. The current study provides the molecular structure-device performance relationship, especially with respect to the alkoxy chain length of Cn-NCBA and their interfacial interactions with P3HT, and suggests a design rule for high-performance fullerene bisadduct acceptors for PSC applications.

Small molecule semiconductors for high-efficiency organic photovoltaics

Organic photovoltaic cells (OPVs) are a promising cost-effective alternative to silicon-based solar cells, and possess light-weight, low-cost, and flexibility advantages. Significant progress has been achieved in the development of novel photovoltaic materials and device structures in the last decade. Nowadays small molecular semiconductors for OPVs have attracted considerable attention, due to their advantages over their polymer counterparts, including well-defined molecular structure, definite molecular weight, and high purity without batch to batch variations. The highest power conversion efficiencies of OPVs based on small molecular donor/fullerene acceptors or polymeric donor/fullerene acceptors are up to 6.7% and 8.3%, respectively, and meanwhile nonfullerene acceptors have also exhibited some promising results. In this review we summarize the developments in small molecular donors, acceptors (fullerene derivatives and nonfullerene molecules), and donor-acceptor dyad systems for high-performance multilayer, bulk heterojunction, and single-component OPVs. We focus on correlations of molecular chemical structures with properties, such as absorption, energy levels, charge mobilities, and photovoltaic performances. This structure-property relationship analysis may guide rational structural design and evaluation of photovoltaic materials (253 references).