Alkylthio Substituents Research Articles

Thiazolothiazole-containing conjugated polymers for indoor organic photovoltaic cells

Organic solar cells (OSCs) have attracted considerable attention in the last few decades due to their unique properties, including lightweight, flexibility, and manufacturing costs. Moreover, OSCs exhibit high performance under ambient light conditions revealing potential applications of these devices in low power electronics and Internet of Things (IoT) systems. In this work, we synthesized and characterized two novel conjugated polymers comprising thiazolothiazole, benzothiadiazole and thiophene alternating blocks with different thioalkyl substituents. Polymer P1 with 2-ethylhexylthio side chains provided power conversion efficiencies of ca. 5.0% on 4.5 cm2 area OSCs fabricated using slot-die coating technique under ambient conditions. Furthermore, the assembled P1-based module delivered the power output of 45.5 μW under 400 lx indoor illumination sufficient to power wireless air temperature sensor, thus demonstrating the potential of our devices for practical indoor applications.

Effects of Heteroatom Substitution on the Photovoltaic Performance of Donor Materials in Organic Solar Cells

ConspectusOver the past few years, the innovation of narrow bandgap acceptor combined with wide bandgap donor materials significantly promotes the power conversion efficiencies (PCEs) of organic solar cells (OSCs) to exceed 18%. To build a state-of-the-art OSC, absorption spectra, frontier molecular orbital energy levels, molecular packing and crystallinity, and charge carrier mobilities of the photovoltaic materials should be considered in their molecular design. The donor and acceptor materials are the key components determining the photovoltaic performance of the OSCs. The side chain engineering on the conjugated backbone is a critical strategy to optimize the photovoltaic properties of the donor materials. In this Account, we focus on the topic of heteroatom substitution on the molecular backbone of the donor materials for improving their photovoltaic performance, aiming to provide in-depth understanding of the molecular structure optimization for the design of state-of-the-art photovoltaic materials.First, we highlight the halogen (fluorine and chlorine) atom substitution strategies applied on the conjugated molecular backbone of the organic photovoltaic materials. The strong electronegativity of halogen atoms can downshift the highest occupied molecular orbital (HOMO) energy levels of the donor materials, which could increase open-circuit voltages of the resulting OSCs. In addition, the hydrogen bonding aroused by the halogen atoms is beneficial to improve their charge transport property and crystallinity of the organic semiconductors. On the other hand, flexible side chains are critical components for improving the solubility of the photovoltaic materials. Using the flexible side chains of alkylthio and alkylsilyl is an easy and effective approach to tune the electronic energy levels and absorption spectra of the photovoltaic materials. Due to the formation of pπ(C)–dπ(S) orbital overlap, the empty 3d-orbitals of the sulfur atom in the alkylthio substituents can accept the π-electron of conjugated skeleton to modulate the optical and electrical properties of the photovoltaic materials. Similarly, the silicon atom in the alkylsilyl side chains can stabilize the lowest unoccupied molecular orbital (LUMO) level and downshift the HOMO level of the organic semiconductor, which leads to the improved photovoltaic performance of the organic donor materials. Finally, we briefly discussed the challenges for the photovoltaic materials toward performance optimization and practical application of the OSCs.

Photodynamic Investigation on the Synergistic Effects of Aromatic Side Chains with Alkylthio Substituents in Nonfullerene Organic Solar Cells

Photodynamic Investigation on the Synergistic Effects of Aromatic Side Chains with Alkylthio Substituents in Nonfullerene Organic Solar Cells

Fine-Tuning Miscibility and π-π Stacking by Alkylthio Side Chains of Donor Molecules Enables High-Performance All-Small-Molecule Organic Solar Cells.

Optimization of morphology and precise control of miscibility between donors and acceptors play an important role in improving the power conversion efficiencies (PCEs) of all-small-molecule organic solar cells (SM-OSCs). Besides device optimization, methods such as additives and thermal annealing are applied for finely tuning bulk-heterojunction morphology; strategies of molecular design are also the key to achieve efficient phase separation. Here, a series of A-D-A-type small-molecule donors (SM4, SM8, and SM12) based on benzodithiophene units were synthesized with different lengths of alkylthio side chains to regulate crystallinity, and their miscibility with the acceptor (BO-4Cl) was investigated. Consequently, SM4 with a short alkylthio substituent had a high crystallization propensity, leading to the oversized molecular domains and the poor morphology of the active layer. Meanwhile, SM12 with a longer alkylthio substituent showed weak crystallinity, causing a relatively looser π-π stacking and thus adversely affecting charge-carrier transport. The SM-OSC based on the small-molecule donor SM8 with a mid-length alkylthio substituent achieved a better PCE over 13%, which was attributed to a more harmonious blend miscibility without sacrificing carrier-charge transport. Eventually, the modulation of phase separation and miscibility via controlling the lateral side chains has proven its potential in optimizing the blend morphology to aid the development of highly efficient SM-OSCs.

5-[Aryloxypyridyl (or nitrophenyl)]-4H-1,2,4-triazoles as novel flexible benzodiazepine analogues: Synthesis, receptor binding affinity and lipophilicity-dependent anti-seizure onset of action

A new series of 5-(2-aryloxy-4-nitrophenyl)-4H-1,2,4-triazoles and 5-(2-aryloxy-3-pyridyl)-4H-1,2,4-triazoles, possessing C-3 thio or alkylthio substituents, was synthesized and evaluated for their benzodiazepine receptor affinity and anti-seizure activity. These analogues revealed similar to significantly superior affinity to GABAA/benzodiazepine receptor complex (IC50 values of 0.04–4.1 nM), relative to diazepam as the reference drug (IC50 value of 2.4 nM). To determine the onset of anti-seizure activity, the time-dependent effectiveness of i.p. administration of compounds on pentylenetetrazole induced seizure threshold was studied and a very good relationship was observed between the lipophilicity (cLogP) and onset of action of studied analogues (r2 = 0.964). The minimum effective dose of the compounds, determined at the time the analogues showed their highest activity, was demonstrated to be 0.025–0.1 mg/kg, relative to diazepam (0.025 mg/kg).

Two‐Dimension Conjugated Acceptors Based on Benzodi(cyclopentadithiophene) Core with Thiophene‐Fused Ending Group for Efficient Polymer Solar Cells

The previously reported nonfullerene small molecule ITIC‐SF achieved via side chain tuning, promotes the power conversion efficiency of polymer solar cells (PSCs) with PBDB‐T‐SF as the donor from 10.1% and ITIC2 acceptors up to 12.2% for ITIC‐SF acceptors. To further this research, benzene end groups of molecules are herein substituted with thiophene rings, obtaining two new molecules BDTCH‐IC with alkylthio substituents, and BDTSF‐IC with alkylthio and fluorine substituents on their thiophene‐conjugated side chains. The absorption edges of BDTCH‐IC and BDTSF‐IC are red‐shifted to 824 and 793 nm, respectively. Strengthened molecular crystallinity, promoted charge extraction, and upgraded morphology endorse the advancement of photovoltaic performance of the small molecular acceptors. Using donor PM6, the two small molecule acceptors show good photovoltaic performance, although the highest occupied molecular orbit energy offsets are small between donor and acceptor materials. As a combination of side‐chain and end‐group engineering, the photovoltaic performance of the PSCs is increased to 13.1%, together with the best short‐circuit current (JSC) and fill factor reported thus far for this series of molecules. The results indicate that the modification of side chain and end groups is an effective way to improve the photovoltaic performance of small molecule acceptors.

Spectroscopic and photophysical properties of mono- and dithiosubstituted BODIPY dyes

A series of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) dyes, substituted at the 3 and 5 positions was synthesized and their spectral and photophysical properties were investigated in solvents of different polarity and polarizability. All compounds are characterized by strong absorption bands at 500–580 nm, corresponding to S0 → S1 transition, the typical for the BODIPY chromophore. Emission spectra are mirror images to absorption with maxima at 520–600 nm. Substitution of the BODIPY chromophore by Cl or thioalkyl substituents induces batochromic shifts in both absorption and emission spectra for 50–60 nm and induces higher quantum yields of fluorescence (Φf = 0.1–0.7). The findings were rationalized by TD-DFT computations. The dyes exhibit weak solvatochromic properties which could not be correlated to solvent polarizability, contrary to majority of BODIPY derivatives. Furthermore, estimated singlet excited state lifetimes (τ = 2–6 ns) reveal that radiative and non-radiative rate constants for deactivation from S1 do not vary with changes in solvent polarity/polarizability. However, the highest values of Φf and τ are generally found in solvents of high polarizability. Presented spectroscopic and photophysical study is important for the use of dyes as chemodosimeters for thiols and cystein, as well as for the rational design of new molecular probes.

Highly Efficient Indoor Organic Solar Cells by Voltage Loss Minimization through Fine-Tuning of Polymer Structures.

Herein, we report a detailed study on the optoelectronic properties, photovoltaic performance, structural conformation, morphology variation, charge carrier mobility, and recombination dynamics in bulk heterojunction solar cells comprising a series of donor-acceptor conjugated polymers as electron donors based on benzodithiophene (BDT) and 5,8-bis(5-bromothiophen-2-yl)-6,7-difluoro-2,3-bis(3-(octyloxy)phenyl)quinoxaline as a function of the BDT's thienyl substitution (alkyl (WF3), alkylthio (WF3S), and fluoro (WF3F)). The synergistic positive effects of the fluorine substituents on the minimization of the bimolecular recombination losses, the reduction of the series resistances (RS), the increment of the shunt resistances (RSh), the suppression of the trap-assisted recombination losses, the balanced charge transport, the finer nanoscale morphology, and the deeper highest occupied molecular orbital (EHOMO) are manifested versus the alkyl and alkylthio substituents. According to these findings, the WF3F:[6,6]-phenyl-C71-butyric acid methyl ester (PC71BM)-based organic photovoltaic device is a rare example that features a high power conversion efficiency (PCE) of 17.34% under 500 lx indoor light-emitting diode light source with a high open-circuit voltage (VOC) of 0.69 V, due to the suppression of the voltage losses, and a PCE of 9.44% at 1 sun (100 mW/cm2) conditions, simultaneously.

Terminal group modification of alkylthio substituted small molecule donor materials for organic solar cells

Side chains and terminal groups have an important effect on photovoltaic performance of organic solar cells (OSCs) based on oligothiophene donor materials. In order to study the effect of alkylthio substituent and different terminal groups on photovoltaic properties, a series of small molecules were designed and synthesized. Molecule LS0 was modified by alkyl as side chains and 2-ethylrhodanine as terminal groups while LS1a, LS1b, LS2, LS3 were substituted with alkylthio side chains and capped with different terminal groups of 2-ethylrhodanine, 2-hexylrhodanine, 2-ethylhexyl cyanoacetate, and 1,3-indanedione, respectively. Compared with LS0, alkylthio substituted LS1a exhibited higher HOMO and LUMO due to more planar backbone. Capped with different terminal groups, LS1a, LS1b, LS2, and LS3 showed the different optical and photovoltaic properties. Among these molecules, OSCs based on LS1b showed the highest power conversion efficiency (PCE) of 8.38% while others showed PCE of 7.87%, 6.52%, 6.52%, and 4.65% for LS0, LS1a, LS2, and LS3, respectively. The results demonstrated that rational selecting side chains and terminal groups could be a promising strategy to promote the performance of small molecule-based OSCs.

Fast and Selective Post-polymerization Modification of Conjugated Polymers Using Dimethyldioxirane.

Modification of functional groups attached to conjugated polymer backbones can drastically alter the material properties. Oxidation of electron-donating thioalkyl substituents to electron-withdrawing sulfoxides or sulfones is a particularly effective modification. However, so far, this reaction has not been studied for the modification of conjugated polymers used in organic electronics. Crucial questions regarding selectivity and reaction time waited to be addressed. Here, we show that the reaction is highly selective and complete within just a few minutes when using dimethyldioxirane (DMDO) for the oxidation of thioalkyl substituents attached to the well-investigated conjugated polymers poly(9-(1-octylnonyl)carbazole-alt-4,7-dithienylbenzothiadiazole) (PCDTBT) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT). The selectivity was confirmed by comparison with polymers obtained from pre-oxidized monomers and by control experiments using related polymers without thioalkyl substituents. Using DMDO, the oxidation yields acetone as the only side-product, which reduces the work-up to mere evaporation of solvents and excessive reagent. Our results show that this oxidation is an exciting method for the preparation of electron-deficient conjugated polymers. It may even allow the preparation of electron acceptors for solar cells directly from the electron donors.

The effect of alkylthio substituents on the photovoltaic properties of conjugated polymers

Abstract Alkylthio groups are effectively utilized in molecule design to improve the performance of polymer solar cells (PSCs). In this study, two conjugated polymers, P1 and P2, were designed and synthesized with alkyl and alkylthio side chains substituted on thiophene as π bridges, respectively. Owing to the twist of the backbone induced by the steric hindrance of the hexyl side chains, polymer P1 shows a low power conversion efficiency (PCE) of 2.83% in PSC devices with PC71BM as acceptor and a low hole mobility of 1.85 × 10−5 cm2 V−1 s−1 in the blend film. In contrast to the steric hindrance of the alkyl side chain, the alkylthio side chain can form S⋯S non-covalent interaction with an adjacent thiophene to maintain the molecular planarity and strengthen intermolecular interaction, which is designed in polymer P2 to improve the photovoltaic performance. As a result, the P2-based devices exhibit a higher PCE of 6.15% with an open-circuit voltage (VOC) of 0.71 V, a short-circuit current (JSC) of 14.55 mA cm−2 and a fill factor (FF) of 59.5%. The hole mobility is also increased to 2.20 × 10−4 cm2 V−1 s−1. Our results demonstrate that introducing S⋯S non-covalent interaction into conjugated polymers could be a useful strategy for building high performance photovoltaic materials.

Side chain engineering in DTBDT-based small molecules for efficient organic photovoltaics.

A new small-molecule donor with a dithieno[2,3-d:2',3'-d']-benzo[1,2-b:4,5-b']-dithiophene (DTBDT) core and both alkyl and alkylthio substituents is designed and synthesized to improve the miscibility between DTBDT-based small molecules and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). The alkyl substituent on the 4-position and the alkylthio substituent on the 5-position of the substituted thiophene are expected to improve intermolecular interactions and prevent severe aggregation of the small molecules. The new small molecule, DTBDT-S-C8-TTR, exhibits a homogenous blend morphology with small domains and edge-on-oriented crystalline structures in blends with PC71BM, and give a maximum power conversion efficiency (PCE) of 8.43%. To recover the crystallinity of the DTBDT-S-C8-TTR small molecules weakened after being blended with PC71BM, a solvent vapor annealing (SVA) treatment is performed. The SVA-treated blend films reveal well-developed crystalline domains with interconnected fibrillar structures. This blend morphology allows efficient charge carrier transport in blends and leads to increased PCEs. The maximum PCE of 9.18% achieved using DTBDT-S-C8-TTR suggests that substituting both alkylthio and alkyl groups into DTBDT can yield small-molecule-based organic photovoltaics (OPVs) displaying improved photovoltaic performances.

Understanding the impact of side-chains on photovoltaic performance in efficient all-polymer solar cells

We performed side-chain fluorination and alkylthio substituent in a template conjugated polymer and further investigate their impact on polymer–polymer solar cell performance.

Introducing alkylthio side chains into acceptor units to improve the photovoltaic performance of a quinoxaline based D-A polymer

Abstract Two new donor-acceptor (D-A) polymers, namely PNDT-QX and PNDT-QXS, with naphtho [1,2-b:5,6-b']dithiophenes (NDT) as donor unit and quinoxaline (QX) as acceptor unit, were designed and synthesized. The difference in the structures of the two polymers is that, in PNDT-QXS the side chains on the QX acceptor units are (2-ethylhexyl) thio thienyl groups, whereas in PNDT-QX the side chains are 2-ethylhexyl thienyl groups, which allow us to systematically compare the effects of alkylthio group on optical, electrochemical, molecular packing properties and PSCs performance of polymers. Our study demonstrated that, relative to alkyl group, alkylthio substituents tune down the HOMO and LUMO energy levels, red-shift and broaden the absorption, and enhance the interchain interaction, therefore significantly affect the BHJ morphology of the copolymer with PC71BM. As a result, the polymer solar cell based on the blend of PNDT-QXS and PC71BM got a highest PCE of 5.03% without using extra post-treatment steps, whereas the PNDT-QX cell only had a 1.93% highest PCE. The results prove for the first time that introducing alkylthio side chains into acceptor moiety would also be an effective strategy for improving the photovoltaic performance of the D-A copolymers.

Bulk Heterojunction Solar Cells: The Role of Alkyl Side Chain on Nanoscale Morphology of Sulfur Over-rich Regioregular Polythiophene/Fullerene Blends

Regioregular HH-TT poly(3,3′-thioalkylbithiophene)s-bearing branched or linear alkyl side-chain substituents (PT2SR) have been synthesized and characterized to investigate their behavior, when used as electron-donor components in blend with a fullerene derivative [[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)] as an electron acceptor, in air-processed photovoltaic solar cells with bulk heterojunction architecture. The optoelectronic characteristics, energy gap, nanoscale morphology, and crystallinity of the blends (PT2SR/PCBM) were examined by ultraviolet–visible spectroscopy, cyclic voltammetry, Kelvin probe force microscopy (KPFM), and X-ray diffraction (XRD). We demonstrate that thioalkyl substituents are able to influence the PCBM self-assembly and the morphology of the polymeric film, important parameters to maximize the efficiency of the solar cell. In particular, the presence of chemical branching in the side chain of the sulfur over-rich polythiophene backbone favors the formation of PCBM clus...

Single-junction fullerene solar cells with 10% efficiency and high open-circuit voltage approaching 1 V

It has been proven that the introduction of F atom and the replacement of alkyl side-chain with alkylthio substituent could be the effective side-chain strategies, to obtain the deep highest occupied molecular orbital (HOMO) energy level with little influence on the optical absorption, and in turn, the small photo energy loss (Eloss). In this work, we combine the advantages of D–A(π)–Q–A(π) strategy and the above side chain engineering, to construct a series of high-performance polymers P1-P3 with high open-circuit voltage (VOC) of exceeding 0.90V in the conventional solar cells. Meanwhile, small Elosss of 0.73–0.78eV are achieved accompanying high VOC and almost unchanged optical bandgaps of ~ 1.70eV, which are the smaller values in comparison with that of the other high-performance polymer systems. More encouragingly, P2-based solar cells exhibit high PCE of 10.30% and VOC of 0.97V, which is one of the highest values for polymer/fullerene based solar cells. Our work not only demonstrates a series of high-efficiency new materials, but also strongly confirms that the combination of D–A(π)–Q–A(π) arrangement and rational side chain engineering is a very promising strategy to construct high-performance photovoltaic polymers with reduced energy loss.

High-Mobility p-Type Organic Semiconducting Interlayer Enhancing Efficiency and Stability of Perovskite Solar Cells.

A high‐mobility p‐type organic semiconductor based on benzodithiophene and diketopyrrolopyrrole with linear alkylthio substituents (BDTS‐2DPP) is used as a dual function interfacial layer to modify the interface of perovskite/2,2′,7,7′‐tetrakis(N,N′‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene in planar perovskite solar cells. The BDTS‐2DPP layer can remarkably passivate the surface defects of perovskite through the formation of Lewis adduct between the under‐coordinated Pb atoms in perovskite and S atoms in BDTS‐2DPP, and also shows efficient hole extraction and transfer properties. The devices with BDTS‐2DPP interlayer show a peak power conversion efficiency of 18.2%, which is higher than that of reference devices without the BDTS‐2DPP interlayer (16.9%). Moreover, the hydrophobic BDTS‐2DPP interlayer effectively protects the perovskite against moisture, leading to enhanced device stability.

Efficient Fullerene-Free Polymer Solar Cells Based on Alkylthio Substituted Conjugated Polymers

A series of medium and wide band gap polymers with different backbones and side-chains were designed and synthesized as electron donors for fullerene-free polymer solar cells (PSCs). The relationship between the molecular structures of the polymer donors and the photovoltaic properties of the fullerene-free PSC devices was fully investigated. The optical band gaps and the energy levels of the polymers were modulated by the copolymerization of the benzodithiophene (BDT) unit with the various comonomers. Moreover, by incorporating alkylthio substituents, the highest occupied molecular orbital (HOMO) levels of the polymer donors were effectively reduced, and thus the open-circuit voltages (Voc) of the fullerene-free PSC devices were strongly improved. Simultaneously, the extinction coefficients of the polymers were also enhanced by introducing the alkylthio groups, which ensured sufficient light-harvesting capability. The exciton dissociation probability P(E,T) in the blend films of the alkylthio substituted...

High efficiency polymer solar cells based on alkylthio substituted benzothiadiazole-quaterthiophene alternating conjugated polymers

We have designed and synthesized two alkylthio substituted benzothiadiazole-quaterthiophene based conjugated polymers (P1 and P2) and investigated their photovoltaic performances. Theoretical simulation has demonstrated that the introduction of alkylthio substituents can increase the planarity of the resulted conjugated polymers. The fluorinated polymer P1 possesses a deeper HOMO energy level than the non-fluorinated polymer P2 and can form well-developed fibril networks when blended with PC71BM. PSCs based on P1:PC71BM (1:1.2, by weight) gave a PCE of 7.76% with a Voc of 0.69 V, a Jsc of 16.30 mA cm−2 and an FF of 0.69. Our results have demonstrated that alkylthiothiophene could be a useful building block for the construction of high efficiency polymer donor materials used for PSCs.

Non-Fullerene Polymer Solar Cells Based on Alkylthio and Fluorine Substituted 2D-Conjugated Polymers Reach 9.5% Efficiency.

Non-fullerene polymer solar cells (PSCs) with solution-processable n-type organic semiconductor (n-OS) as acceptor have seen rapid progress recently owing to the synthesis of new low bandgap n-OS, such as ITIC. To further increase power conversion efficiency (PCE) of the devices, it is of a great challenge to develop suitable polymer donor material that matches well with the low bandgap n-OS acceptors thus providing complementary absorption and nanoscaled blend morphology, as well as suppressed recombination and minimized energy loss. To address this challenge, we synthesized three medium bandgap 2D-conjugated bithienyl-benzodithiophene-alt-fluorobenzotriazole copolymers J52, J60, and J61 for the application as donor in the PSCs with low bandgap n-OS ITIC as acceptor. The three polymers were designed with branched alkyl (J52), branched alkylthio (J60), and linear alkylthio (J61) substituent on the thiophene conjugated side chain of the benzodithiophene (BDT) units for studying effect of the substituents on the photovoltaic performance of the polymers. The alkylthio side chain, red-shifted absorption down-shifted the highest occupied molecular orbital (HOMO) level and improved crystallinity of the 2D conjugated polymers. With linear alkylthio side chain, the tailored polymer J61 exhibits an enhanced JSC of 17.43 mA/cm(2), a high VOC of 0.89 V, and a PCE of 9.53% in the best non-fullerene PSCs with the polymer as donor and ITIC as acceptor. To the best of our knowledge, the PCE of 9.53% is one of the highest values reported in literature to date for the non-fullerene PSCs. The results indicate that J61 is a promising medium bandgap polymer donor in non-fullerene PSCs.