Benzodithiophene Core Research Articles

19% efficiency in organic solar cells of Benzo[1,2-b:4,5-b′]Difuran-based donor polymer realized by volatile + non-volatile dual-solid-additive strategy

Though the application-promising photovoltaic technology named organic solar cells (OSCs) have been close to 20% benchmark power conversion efficiency (PCE) within fabrication friendly single-junction devices, these achievements are enabled by polymer donors based on benzodithiophene cores, requiring toxic production steps. Whilst, the bio-renewable benzo[1,2-b:4,5-b′]difuran unit constructed polymer donors cannot yield comparable efficiency, though their lower steric hindrance is widely appreciated. OSC field has paid great attention on optimizing their performance by chemistry design, yet the device engineering is relatively neglected compared to what have been done on the benzodithiophene side. Here we report a new dual additive strategy of simultaneously applying volatile (2-CN) and non-volatile (MF) solid additives to reduce non-radiative voltage loss and boost charge generation, via an occupying evaporated left vacancies in polymer matrix process. Consequently, the target system D18-Fu:L8-BO’s efficiency is promoted to 19.11%, representing the cutting-edge level of this research topic.

Influence of chirality on the aggregation of a new A-π-D-π-A small molecule with a benzodithiophene core: Spectroscopic and morphological investigations

In this paper, the synthesis and characterization of a new alkoxy benzodithiophene-based small molecule bearing two stereocenters and two end-capping acetyl groups (BDTCOR) are reported. The molecule has been obtained in both enantiopure form (S, S) and stereoisomeric mixture. The spectroscopic properties of BDTCOR in solution were compared to computational data revealing that the molecule is a candidate for optoelectronic applications thanks to a broad UV–Vis absorption spectrum and suitable fluorescence properties. The molecule was deposited as a thin film by physical vapor deposition on SiO2 and PMMA substrates revealing a quite different behavior of the enantiopure form vs. the stereoisomeric mixture. In particular, significant differences were found in film morphology suggesting that, contrary to what observed for the stereoisomeric mixture, enantiopure BDTCOR tends to generate supramolecular well-ordered structures. Moreover, while electronic circular dichroism spectra of enantiopure BDTCOR casted films do not show significant signals, vapor-deposited films show intense Cotton effect, suggesting a synergic role of chirality and of the deposition technique on the molecular order.

Thermal-responsive ground-state spin switching in novel butterfly-shaped overcrowded ethylene featuring a benzodithiophene core

The polycyclic aromatic heterocycle of benzodithiophene has been employed as the core structure for synthesizing butterfly-shaped overcrowded ethylene, which exhibits thermal-responsive ground-state spin switching characteristics.

Ternary organic solar cells with a selenophene-containing donor guest achieve a high efficiency of 18.41%

A selenophene-containing and chlorinated benzodithiophene based guest donor endows the ternary organic solar cells with a high efficiency of 18.41%.

Effect of alkylthiolated hetero-aromatic rings on the photovoltaic performance of benzodithiophene-based polymer/fullerene solar cells

Three new donor–acceptor (D–A) copolymers based on benzodithiophene (BDT) with alkylthiolated aromatic rings furan, thiophene, and benzene and 5,6-difluoro-4,7-bis(4-(2-octyldodecyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole (DTBT) units, namely PBDTFS-DTBT, PBDTTS-DTBT, and PBDTPS-DTBT, respectively, were synthesized and applied in solution-processed fullerene type organic solar cells (OSCs). The target polymers were systematically investigated by thermogravimetric analysis (TGA), ultraviolet-visible (UV–vis) absorption spectra, cyclic voltammetry (CV), density functional theory (DFT) and photovoltaic measurements. The experimental results imply that the electron push-pull effect and torsion angles between the conjugated side hetero-aromatic rings and BDT core play a key role in tuning the optical absorption bands, molecular energy levels, hole mobilities, and morphology of the corresponding polymers. The OSCs based on PBDTTS-DTBT and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) show the highest power conversion efficiency (PCE) of 7.80% among the three polymeric analogues, with an open-circuit voltage (Voc) of 0.92 V, a short-circuit current density (Jsc) of 11.95 mA cm−2 and fill factor (FF) of 70.76%. Hence, the results in this work indicate that the photovoltaic properties of the BDT-BT-based polymers can be effectively modulated by introducing conjugated alkylthiolated hetero-aromatic rings with the varied electron donating ability and steric hindrance.

Efficient Electron Transport Layer Free Small-Molecule Organic Solar Cells with Superior Device Stability.

Electron transport layers (ETLs) placed between the electrodes and a photoactive layer can enhance the performance of organic solar cells but also impose limitations. Most ETLs are ultrathin films, and their deposition can disturb the morphology of the photoactive layers, complicate device fabrication, raise cost, and also affect device stability. To fully overcome such drawbacks, efficient organic solar cells that operate without an ETL are preferred. In this study, a new small-molecule electron donor (H31) based on a thiophene-substituted benzodithiophene core unit with trialkylsilyl side chains is designed and synthesized. Blending H31 with the electron acceptor Y6 gives solar cells with power conversion efficiencies exceeding 13% with and without 2,9-bis[3-(dimethyloxidoamino)propyl]anthra[2,1,9-def:6,5,10-d'e'f ']diisoquinoline-1,3,8,10(2H,9H)-tetrone (PDINO) as the ETL. The ETL-free cells deliver a superior shelf life compared to devices with an ETL. Small-molecule donor-acceptor blends thus provide interesting perspectives for achieving efficient, reproducible, and stable device architectures without electrode interlayers.

Effect of Side-Chain Modification on the Active Layer Morphology and Photovoltaic Performance of Liquid Crystalline Molecular Materials.

Controlling the nanoscale morphology of the photoactive layer by fine-tuning the molecular structure of semiconducting organic materials is one of the most effective ways to improve the power conversion efficiency of organic solar cells. In this contribution, we investigate the photovoltaic performance of benzodithiophene (BDT)-based p-type small molecules with three different side chains, namely alkyl-thio (BTR-TE), dialkylthienyl (BTR), and trialkylsilyl (BTR-TIPS) moieties substituted on the BDT core, when used alongside a nonfullerene acceptor. The side-chain changes on the BDT core are shown to have a profound effect on energy levels, charge generation, recombination, morphology, and photovoltaic performance of solid-state molecules. Compared with BTR and BTR-TIPS, BTR-TE-based single-junction binary blend solar cells show the best power conversion efficiency (PCE) of 13.2% due to improved morphology and charge transport with suppressed recombination. In addition, we also achieved relatively good performances for ternary blend solar cells with a PCE of 16.1% using BTR-TE as a third component. Our results show that side-chain modification has a significant effect on modulating active layer morphology, and in particular that thioether side-chain modification is an effective way to achieve optimum morphology and performance for organic photovoltaic (OPV) devices.

Synthesis and photovoltaic properties of organic molecules based on difluoroquinoxaline derivatives for OPVs

We designed and synthesized two novel low band gap small molecule donors (M1 and M2) that consist of benzo[1,2-b:4,5-b′]dithiophene as the electron-rich core and 6,7-difluoroquinoxaline as the electron-deficient end-group. M1 and M2 with A-D-A type structure were synthesized via Stille coupling reaction for use in OSCs. The absorption maximum of the M1 and M2 in solid thin films exhibited at 536 and 540 nm and absorption onset at 582 and 592 nm, corresponding to band gaps of 2.31 and 2.10 eV, respectively. Although the absorption of the M1 with branched alkyl chain was blue shifted as compared to M2, the branched alkyl chain in benzodithiophene core provide appropriate solubility to provide good OSC performance.

End group tuning in small molecule donors for non-fullerene organic solar cells

Two novel small molecules, which consist of electron donating benzodithiophene core bridged through bithiophene π-spacer with terminal either dicyanovinyl (DCV-Me) or n-butyl cyanoester (CNAB) electron-withdrawing groups, were designed and used as donor materials for all-small molecule OSCs (all-SM-OSCs) with a non-fullerene acceptor (IDIC). The novel donor oligomers were firstly characterized by thermal gravimetric analysis, differential scanning calorimetry, UV–Vis spectroscopy, and cyclic voltammetry as well as studied by density functional theory calculations. The simple change of the DCV-Me to CNAB group leads to more pronounced crystallinity, higher solubility and higher energy levels in the donor BDT-2T-CNAB. The photovoltaic devices based on the BDT-2T-CNAB:IDIC blend exhibit higher short-circuit current (Jsc) and fill factor, and thus much higher power conversion efficiency (PCE) of 6.17% than those of BDT-2T-DCV-Me:IDIC devices (1.56%). Compared to the BDT-2T-DCV-Me system, the BDT-2T-CNAB based device shows smoother film surface morphology, and superior exciton dissociation, charge generation and charge carrier mobilities as well as lower non-geminate recombination losses. The results clearly demonstrate that the design of new small molecule donors for high-performance all-SM-OSCs should aim to choose suitable end acceptor units, among which the alkyl cyanoester groups are one of the most promising.

Impact of 9‐(4‐methoxyphenyl) Carbazole and Benzodithiophene Cores on Performance and Stability for Perovskite Solar Cells Based on Dopant‐Free Hole‐Transporting Materials

Perovskite solar cells (PSCs) possess both high‐power conversion efficiency (PCE) and good operation stability for future application. Although many different types of hole‐transporting materials (HTMs) are assessed, few dopant‐free small organic molecule HTMs‐based PSC cells exist, which exhibit excellent stability under both heat and illumination. Herein, two novel HTMs that are based on 9‐(4‐methoxyphenyl) carbazole and benzodithiophene cores are synthesized and named N1,N1′‐(9‐(4‐methoxyphenyl)‐9H‐carbazole‐3,6‐diyl)bis(N1‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)‐N4,N4‐bis(4‐methoxyphenyl)benzene‐1,4‐diamine) (PhCz‐4MeOTPA) and N1,N1′‐(benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(N1‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)‐N4,N4‐bis(4‐methixyphenyl)benzene‐1,4‐diamine) (BDT‐4MeOTPA). Of the two HTMs, PhCz‐4MeOTPA possesses a lower level of planarity than that of BDT‐4MeOTPA, which inhibits molecular stacking to improve film quality and increases hole‐transport mobility and charge transport. A PCE of 16.04% is achieved with the application of dopant‐free PhCz‐4MeOTPA in PSCs, which is higher than that of dopant‐free BDT‐4MeOTPA. The unencapsulated PSC devices based on PhCz‐4MeOTPA maintain 82% of their initial values under continuous sun illumination in an ambient environment at 40–45 °C after 672 h and 92% of their initial values at 80 °C in an ambient environment after 1200 h in the dark.

A versatile star-shaped organic semiconductor based on benzodithiophene and diketopyrrolopyrrole

A novel star-shaped π-conjugated oligomer containing a benzodithiophene core and four diketopyrrolopyrrole arms is reported.

Near-infrared non-fullerene acceptors based on dithienyl[1,2-b:4,5-b’]benzodithiophene core for high performance PTB7-Th-based polymer solar cells

Two non-fullerene electron acceptors (BT-SFIC and BT-FIC) bearing a dithienyl[1,2-b:4,5-b’]benzodithiophene core were designed and synthesized. Due to the strong electron-withdrawing ability of fluorine atoms, these two non-fullerene acceptors both show near-infrared absorption around 900 nm, with a narrow bandgap of 1.44 and 1.39 eV for BT-SFIC and BT-FIC, respectively. BT-SFIC and BT-FIC have complementary absorption and matched energy level with PTB7-Th. PSCs based on PTB7-Th donor and these two acceptors both show good charge dissociation and collection, small charge recombination and good active layer morphology. However, BT-FIC bearing much more fluorine have much higher electron mobility. And the PSCs based on PTB7-Th: BT-FIC gives a maximum PCE of 10.10% with a VOC of 0.73 eV, a JSC of 21.28 mA cm−2 and an FF of 65%, which is among in the high-performance polymer organic solar cells based on PTB7-Th.

To be or not to be – nematic liquid crystals from shape-persistent V-shaped nematogens with the ‘magic angle’

ABSTRACTThe tetrahedral bending angle in V-shaped nematogens was claimed to be the optimum for finding a biaxial nematic liquid crystal phase. The benzo[1,2-b:4,3-b’]dithiophene core, recently successfully applied as a tetrahedral bending unit in mesogens with lateral flexible chains, is here embedded in a scaffold with only terminal chains, which conventionally promotes the formation of nematic phases at low temperature. A series of new mesogens has been successfully prepared, realising hockey-stick, hockey-stick dimer and V-shaped molecular topologies. Only the hockey-stick mesogens assemble in uniaxial nematic phases over a broad temperature range. Single crystal structure analysis of a hockey-stick and V-shaped compound reveal remarkable similarities with the benzodithiophene core wrapped by aliphatic chains. A model explaining the absence of nematic mesophases in the family of V-shaped, shape-persistent mesogens with terminal aliphatic chains is presented and results in the proposal of a new design for biaxial nematogens.

New Wide Band Gap Donor for Efficient Fullerene-Free All-Small-Molecule Organic Solar Cells.

A new organic small molecule, DRTB-T, that incorporates a two-dimensional trialkylthienyl-substituted benzodithiophene core building block was designed and synthesized. DRTB-T has a band gap (Egopt) of 2.0 eV with a low-lying highest occupied molecular orbital (HOMO) level of -5.51 eV. Nonfullerene small-molecule solar cells consisting of DRTB-T and a nonfullerene acceptor (IC-C6IDT-IC) were constructed, and the morphology of the active layer was fine-tuned by solvent vapor annealing (SVA). The device showed a record 9.08% power conversion efficiency (PCE) with a high open-circuit voltage (Voc = 0.98 V). This is the highest PCE for a nonfullerene small-molecule organic solar cell (NFSM-OSC) reported to date. Our notable results demonstrate that the molecular design of a wide band gap (WBG) donor to create a well-matched donor-acceptor pair with a low band gap (LBG) nonfullerene small-molecule acceptor, as well as subtle morphological control, provides great potential to realize high-performance NFSM-OSCs.

The A-D-A type small molecules with isomeric benzodithiophene cores: Synthesis and influence of isomers on photoelectronic properties

Two isomeric A-D-A type small molecules (SMs) of BDTx-2TVTDPP and BDTy-2TVTDPP were designed and synthesized, which contain different donor (D) center of substituted benzodithiophene (BDT) in backbone, and the same acceptor (A) and bridged units of diketopyrrolopyrrole (DPP) and thienylenevinylenethiophene (TVT), respectively. Their thermal stability, crystallinity, film morphology and photoelectronic properties were primarily investigated. It was found the BDTx-2TVTDPP with 2,6-substituted BDT unit exhibited a pronouncedly red-shifted and enhanced absorption in solid state and a better crystallinity. In contrast, the BDTy-2TVTDPP with 4,8-substituted BDT unit in backbone exhibited better solubility, deeper HOMO energy level and more smoothed blend film morphology. As a result, the solution-processing BDTy-2TVTDPP based solar cells displayed better photovoltaic properties than the BDTx-2TVTDPP based ones using fullerene derivatives (PC61BM or PC71BM) as electron acceptor. A power conversion efficiency maximum of 2.85% was obtained in the BDTy-2TVTDPP based cells, which is 1.8 times that of the BDTx-2TVTDPP based cells. This study indicates that changing the substituted positions of BDT is available to significantly improve photovoltaic properties for its resulting SMs.

Benzodithiophene based organic dyes for DSSC: Effect of alkyl chain substitution on dye efficiency

A series of push–pull triarylamine organic dyes containing the benzo[1,2-b:4,5-b′]dithiophene unit as a spacer and bearing alkyl chains in different positions of the molecule were synthesized. The new dyes 1–4 were characterized by optical and electrochemical measurements and density functional theory calculations and used as sensitizers in liquid dye-sensitized solar cells. The effect of alkyl chain position on dye properties and performances was investigated and dye 1, bearing two 3,7-dimethyloctyl groups on the benzodithiophene core, exhibited the best behaviour in term of light absorption and cell performance (PCE of 6.6%, to be compared with a PCE of 8.1% for N719-based device). The efficiency of the DSSC was highly dependent on the solvent used for the dye-sensitizing bath, which affects the position of the COOH/COO− equilibrium.

Oriented Thin Films of a Benzodithiophene Covalent Organic Framework

A mesoporous electron-donor covalent organic framework based on a benzodithiophene core, BDT-COF, was obtained through condensation of a benzodithiophene-containing diboronic acid and hexahydroxytriphenylene (HHTP). BDT-COF is a highly porous, crystalline, and thermally stable material, which can be handled in air. Highly porous, crystalline oriented thin BDT-COF films were synthesized from solution on different polycrystalline surfaces, indicating the generality of the synthetic strategy. The favorable orientation, crystallinity, porosity, and the growth mode of the thin BDT-COF films were studied by means of X-ray diffraction (XRD), 2D grazing incidence diffraction (GID), transmission and scanning electron microscopy (TEM, SEM), and krypton sorption. The highly porous thin BDT-COF films were infiltrated with soluble fullerene derivatives, such as [6,6]-phenyl C61 butyric acid methyl ester (PCBM), to obtain an interpenetrated electron-donor/acceptor host–guest system. Light-induced charge transfer from the BDT-framework to PCBM acceptor molecules was indicated by efficient photoluminescence quenching. Moreover, we monitored the dynamics of photogenerated hole-polarons via transient absorption spectroscopy. This work represents a combined study of the structural and optical properties of highly oriented mesoporous thin COF films serving as host for the generation of periodic interpenetrated electron-donor and electron-acceptor systems.

Effect of the Substitution Pattern of Alkyl Side Chain in a Benzodithiophene Core π-System on Intra and Inter-Molecular Charge Carrier Mobility

Effect of the Substitution Pattern of Alkyl Side Chain in a Benzodithiophene Core π-System on Intra and Inter-Molecular Charge Carrier Mobility

Effect of the Substitution Pattern of Alkyl Side Chain in a Benzodithiophene Core π-System on Intra and Inter-Molecular Charge Carrier Mobility

3,7-Didocecyl-2,6-di(5-phenylthiophen-2-yl)benzo[1,2-b:3,4-b']dithiophene (1) and its 4,8-didodecyl isomer 2 were prepared as the representative soluble X- and cross-shaped π-conjugated oligomer systems to provide insight into the effect of the substitution pattern of the alkyl side chain on electronic properties. The absorption and emission spectra as well as CV data showed the relatively longer effective conjugation of cross-shaped 2. The intrinsic charge-carrier mobilities were then estimated by flash-photolysis time-resolved microwave conductivity (FP-TRMC) method and compared with their top contact FET properties. It was found that, although the TRMC method showed the higher mobility of 2 than 1, the FET performance of 1 after appropriate conditioning and thermal annealing was superior to that of 2. The effective conjugation of cross-shaped 2 is well reflected in the intramolecular mobility of positive holes estimated by FP-TRMC, showing striking contrast to the rather higher mobility of X-shaped 1 observed by FET as well as TOF measurements as the long-range translational motion of the carriers. This strongly suggests that the intermolecular packing of these compounds plays a significant role in the range of hole mobility of <∼10(-2) cm(2) V(-1) s(-1).

Polymers Containing Rigid Benzodithiophene Repeating Unit with Extended Electron Delocalization

Polymers containing a fused benzodithiophene core with phenylethynyl substituents were prepared. The parent poly[4,8-bis(4-pentylphenylethynyl)benzo[1,2-b:4,5-b']dithiophene] was prepared by a Stille coupling. Copolymers with the new core were also obtained by Stille coupling with dibrominated fluorene and carbazole monomers. The obtained polymers had a lower band gap as compared to the related benzodithiophene cores due to the extended electron conjugation. The polymers were also highly fluorescent as observed by high quantum yields.