Recent progress in the design of narrow bandgap conjugated polymers for high-efficiency organic solar cells

An Intervention into the Diverse Utilities of Fluorenes: A Brobdingnagian Family

The keyword "Fluorene" search in SciFinder found more than 57,000 results, including high-impact journal articles, review articles, patents, books, proceedings, etc. Against this background, a detailed enquiry has been made by our group on various classes of fluorenes and their relevancy. For the past several decades, fluorene and its related compounds have experienced extensive studies, which are attributed to the vast range of applications they possess in various fields like sensors, polymers, OLED devices and even in the pharmaceutical industries. Since fluorene is an important member of the 'polyaromatic-hydrocarbon' family and has proved its relevancy in multidisciplinary areas, summarising those milestones might be worthwhile for future researchers. Here, we intend to highlight the key applications of fluorene derivatives in the form of a review article and have put much effort into consolidating some of their most imperative applications, including those in sensors and medicinal, optoelectronic and electrochemical fields. The manuscript divides the fluorene family into multiple subclasses, counting mono- and polyfluorenes, spirofluorenes, silicon-cored fluorenes, indenofluorenes, etc., based on their structure, and portrays all the critical properties of each class. Since fluorenes are globally accepted as outstanding candidates for numerous applications and practicalities, our effort may find crucial acceptance in the near future.

Design, Synthesis, and Theoretical Studies on the Benzoxadiazole and Thienopyrrole Containing Conjugated Random Copolymers for Organic Solar Cell Applications

In this study, six different donor-π-acceptor1-π-donor-acceptor2 type random co-polymers containing benzodithiophene as a donor, benzooxadiazole (BO), and thieno[3,4-c]pyrrole-4,6-dione (TPD) as acceptor, have been synthesized and characterized. In addition to the acceptor core ratio at different values, the effect of aromatic bridge structures on the optical, electronic, and photovoltaic properties of six different random co-polymers is investigated by using thiophene and selenophene structures as aromatic bridge units. To investigate how the acceptor unit ratio and replacement of aromatic bridge units impact the structural, electronic, and optical properties of the polymers, density functional theory (DFT) calculations are carried out for the tetramer models. The open-circuit voltage (VOC), which is strongly correlated with the HOMO levels of the donor material, is enhanced with the increasing ratio of the TPD moiety. On the other hand, the short-circuit current (JSC), which is associated with the absorption ability of the donor material, is improved by the increasing ratio of BO moiety with the π-bridges. BO moiety dominant selenophene π-bridged co-polymer (P4) showed the best performance with a power conversion efficiency (PCE) of 6.26%, a JSC of 11.44 mA cm2, a VOC of 0.80 V, and a fill factor (FF) of 68.81%.

Continuous Topological Transition and Bandgap Tuning in Ethynylene-Linked Acene π-Conjugated Polymers through Mechanical Strain

By variation of the chemical repeat units of conjugated polymers, only discrete tuning of essential physical parameters is possible. A unique property of a class of π-conjugated polymers, where polycyclic aromatic hydrocarbons are linked via ethynylene linkers, is their topological aromatic to quinoid phase transition discovered recently by Cirera et al. and González-Herrero et al., which is controllable in discrete steps by chemical variations. We have discovered by means of density functional theory computations that such a phase transition can be achieved by applying continuous variations of longitudinal strain, allowing us to tune the bond length alternation and bandgap. At a specific strain value, the bandgap becomes zero due to an orbital level crossing between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). Our hypothesis provides a perspective on the design of organic electronic materials and provides a novel insight into the properties of a continuous phase transition in topological semiconducting polymers.

Hussein A. A Mini Review on the Development of Conjugated Polymers: Steps towards the Commercialization of Organic Solar Cells

This review article covers the synthesis and design of conjugated polymers for carefully adjusting energy levels and energy band gap (EBG) to achieve the desired photovoltaic performance. The formation of bonds and the delocalization of electrons over conjugated chains are both explained by the molecular orbital theory (MOT). The intrinsic characteristics that classify conjugated polymers as semiconducting materials come from the EBG of organic molecules. A quinoid mesomeric structure (D-A ↔ D⁺ = A^-) forms across the major backbones of the polymer as a result of alternating donor-acceptor segments contributing to the pull-push driving force between neighboring units, resulting in a smaller optical EBG. Furthermore, one of the most crucial factors in achieving excellent performance of the polymer is improving the morphology of the active layer. In order to improve exciton diffusion, dissociation, and charge transport, the nanoscale morphology ensures nanometer phase separation between donor and acceptor components in the active layer. It was demonstrated that because of the exciton's short lifetime, only small diffusion distances (10-20 nm) are needed for all photo-generated excitons to reach the interfacial region where they can separate into free charge carriers. There is a comprehensive explanation of the architecture of organic solar cells using single layer, bilayer, and bulk heterojunction (BHJ) devices. The short circuit current density (J_sc), open circuit voltage (V_oc), and fill factor (FF) all have a significant impact on the performance of organic solar cells (OSCs). Since the BHJ concept was first proposed, significant advancement and quick configuration development of these devices have been accomplished. Due to their ability to combine great optical and electronic properties with strong thermal and chemical stability, conjugated polymers are unique semiconducting materials that are used in a wide range of applications. According to the fundamental operating theories of OSCs, unlike inorganic semiconductors such as silicon solar cells, organic photovoltaic devices are unable to produce free carrier charges (holes and electrons). To overcome the Coulombic attraction and separate the excitons into free charges in the interfacial region, organic semiconductors require an additional thermodynamic driving force. From the molecular engineering of conjugated polymers, it was discovered that the most crucial obstacles to achieving the most desirable properties are the design and synthesis of conjugated polymers toward optimal p-type materials. Along with plastic solar cells (PSCs), these materials have extended to a number of different applications such as light-emitting diodes (LEDs) and field-effect transistors (FETs). Additionally, the topics of fluorene and carbazole as donor units in conjugated polymers are covered. The Stille, Suzuki, and Sonogashira coupling reactions widely used to synthesize alternating D-A copolymers are also presented. Moreover, conjugated polymers based on anthracene that can be used in solar cells are covered.

Modulating the Chiroptical Response of Chiral Polymers with Extended Conjugation within the Structural Building Blocks

Advancing the emerging area of chiral photonics requires modeling-guided concepts of chiral material design to enhance optical activity and associated optical rotatory dispersion. Herein, we introduce conformational engineering achieved by tuning polymer backbone conjugation through introduction of thiophene structural units in a chiral fluorene polymer backbone. Our theoretical calculations reveal a relationship between the structural conformation and the resultant rotational strength. We further synthesize a series of chiral fluorene-based polymers copolymerized with thiophene whose optical chirality trend is in qualitative agreement with predictions of our quantum chemical calculations. Varying the number of thiophene units in the monomer building block allows us to modulate the rotational strength by tuning the intrafibril helicity of single-stranded polymer chains, whereby the monomer conjugation is retained throughout the whole length of the polymer backbone. Our design concept delineates an underexamined approach: the concept of tuning backbone conjugation and helicity within the main chain to enhance the optical activity of chiral polymer systems.

Indane-1,3-Dione: From Synthetic Strategies to Applications

Indane-1,3-dione is a versatile building block used in numerous applications ranging from biosensing, bioactivity, bioimaging to electronics or photopolymerization. In this review, an overview of the different chemical reactions enabling access to this scaffold but also to the most common derivatives of indane-1,3-dione are presented. Parallel to this, the different applications in which indane-1,3-dione-based structures have been used are also presented, evidencing the versatility of this structure.

Designing small organic non-fullerene acceptor molecules with diflorobenzene or quinoline core and dithiophene donor moiety through density functional theory

The non-fullerene acceptors A1-A5 with diflourobenzene or quinoline core (bridge) unit, donor cyclopenta[1,2-b:3,4-b']dithiophene unit and 2-(2-methylene-3-oxo-2,3-dihydro-1H-inden-1-ylidene)malononitrile as acceptor unit with additional phenyl, fulvene or thieno[3,2-d]pyrimidinyl 5-oxide groups have been designed through DFT calculations. The optimization of molecular geometries were performed with density functional theory (DFT) at B3LYP 6-31G (d,p) level of theory. The frontier molecular orbital (FMO) energies, band gap energies and dipole moments (ground and excited state) have been calculated to probe the photovoltaic properties. The band gap (1.42-2.01 eV) and dipole moment values (5.5-18. Debye) showed that these designed acceptors are good candidates for organic solar cells. Time-Dependent Density Functional Theory (TD-DFT) results showed λmax (wave length at maximum absorption) value (611-837 nm), oscillator strength (f) and excitation energies (1.50-2.02 eV) in gas phase and in CHCl3 solvent (1.48-1.89 eV) using integral equation formalism variant (IEFPCM) model. The λmax in CHCl3 showed marginal red shift for all designed acceptors compared with gas phase absorption. The partial density of states (PDOS) has been plotted by using multiwfn which showed that all the designed molecules have more electronic distribution at the donor moiety and lowest at the central bridge. The reorganization energies of electron (λe) (0.0007 eV to 0.017 eV), and the hole reorganization energy values (0.0003 eV to - 0.0403 eV) were smaller which suggested that higher charged motilities. The blends of acceptors A1-A5 with donor polymer D1 provided open circuit voltage (Voc) and ∆HOMO off-set of the HOMO of donor and acceptors. These blends showed 1.04 to 1.5 eV values of Voc and 0 to 0.38 eV ∆HOMO off set values of the donor-acceptor bends which indicate improved performance of the cell. Finally, the blend of D1-A4 was used for the study of distribution of HOMO and LUMO. The HOMO were found distributed on the donor polymer (D1) while the A4 acceptor was found with LUMO distribution. Based on λmax values, and band gap energies (Eg), excitation energies (Ex), reorganization energies; the A3 and A4 will prove good acceptor molecules for the development of organic solar cells.

Degradable polymers via olefin metathesis polymerization

The development of degradable polymers has commanded significant attention over the past half century. Approaches have predominantly relied on ring-opening polymerization of cyclic esters (e.g., lactones, lactides) and N-carboxyanhydrides, as well as radical ring-opening polymerizations of cyclic ketene acetals. In recent years, there has been a significant effort applied to expand the family of degradable polymers accessible via olefin metathesis polymerization. Given the excellent functional group tolerance of olefin metathesis polymerization reactions generally, a broad range of conceivable degradable moieties can be incorporated into appropriate monomers and thus into polymer backbones. This approach has proven particularly versatile in synthesizing a broad spectrum of degradable polymers including poly(ester), poly(amino acid), poly(acetal), poly(carbonate), poly(phosphoester), poly(phosphoramidate), poly(enol ether), poly(azobenzene), poly(disulfide), poly(sulfonate ester), poly(silyl ether), and poly(oxazinone) among others. In this review, we will highlight the main olefin metathesis polymerization strategies that have been used to access degradable polymers, including (i) acyclic diene metathesis polymerization, (ii) entropy-driven and (iii) enthalpy-driven ring-opening metathesis polymerization, as well as (iv) cascade enyne metathesis polymerization. In addition, the livingness or control of polymerization reactions via different strategies are highlighted and compared. Potential applications, challenges and future perspectives of this new library of degradable polyolefins are discussed. It is clear from recent and accelerating developments in this field that olefin metathesis polymerization represents a powerful synthetic tool towards degradable polymers with novel structures and properties inaccessible by other polymerization approaches.

An unfused-ring acceptor with high side-chain economy enabling 11.17% as-cast organic solar cells

Side-chain engineering on nonfullerene acceptors (NFAs) is crucial for modulating their solubility and crystallinity as well as packing behaviours in active layers to pursue high-performance organic solar cells (OSCs). High weight ratios of side chains are generally used by NFAs for the desired device efficiencies. Side-chain economy has seldom been discussed despite increased cost and difficulties in synthesis when optimizing the molecular design. Herein, we introduce 7H-dibenzo[c,g]carbazole (DCB) as an electron-donating core to design unfused-ring acceptors (UFAs) with a dramatically low weight ratio of side chains. DCB-4F has thus been designed and compared with the carbazole cored analogue (CB-4F). The unique conformation of the DCB core endows DCB-4F with higher solubility (8.2 mg mL^-1 in chloroform) compared to CB-4F (2.2 mg mL^-1) when using the same side chains. Featuring a lowest unoccupied molecular orbital (LUMO) level of -3.86 eV and an optical bandgap of 1.55 eV, the DCB-4F film exhibits an absorption profile (maximum 667 nm) complementary to polymer donor PM6. The PM6:DCB-4F as-cast OSCs deliver a power conversion efficiency (PCE) of 9.56% with a high open-circuit voltage (V_OC) of 1.00 V. By adding 10 wt% PC₇₁BM into the casting solutions, a greatly improved PCE of 11.17% is readily achieved, which is one of the highest PCEs for as-cast single-junction UFA-based devices. The PM6:DCB-4F based blends show homogeneous nano-fiberous morphology and higher hydrophobicity. The design of conformation-tuned NFAs using sterically hindered DCB-like cores is promising to achieve highly efficient as-cast OSCs.

Abdullah S, Brza MA, Abdulwahid RT. Influence of Fluorine Substitution on the Optical, Thermal, Electrochemical and Structural Properties of Carbazole-Benzothiadiazole Dicarboxylic Imide Alternate Copolymers

In this work four novel donor-acceptor copolymers, PCDTBTDI-DMO, PCDTBTDI-8, P2F-CDTBTDI-DMO and P2F-CDTBTDI-8, were designed and synthesised via Suzuki polymerisation. The first two copolymers consist of 2,7-carbazole flanked by thienyl moieties as the electron donor unit and benzothiadiazole dicarboxylic imide (BTDI) as electron acceptor units. In the structures of P2F-CDTBTDI-DMO and P2F-CDTBTDI-8 copolymers, two fluorine atoms were incorporated at 3,6-positions of 2,7-carbazole to investigate the impact of fluorine upon the optoelectronic, structural and thermal properties of the resulting polymers. P2F-CDTBTDI-8 possesses the highest number average molecular weight (Mn = 24,200 g mol-1) among all the polymers synthesised. PCDTBTDI-DMO and PCDTBTDI-8 show identical optical band gaps of 1.76 eV. However, the optical band gaps of fluorinated copolymers are slightly higher than non-fluorinated counterparts. All polymers have deep-lying highest occupied molecular orbital (HOMO) levels. Changing the alkyl chain substituents on BTDI moieties from linear n-octyl to branched 3,7-dimethyloctyl groups as well as substituting the two hydrogen atoms at 3,6-positions of carbazole unit by fluorine atoms has negligible impact on the HOMO levels of the polymers. Similarly, the lowest unoccupied molecular orbital (LUMO) energy levels are almost comparable for all polymers. Thermogravimetric analysis (TGA) has shown that all polymers have good thermal stability and also confirmed that the fluorinated copolymers have higher thermal stability relative to those non-fluorinated analogues. Powder X-ray diffraction (XRD) studies proved that all polymers have an amorphous nature in the solid state.

Discovery of Self-Assembling π-Conjugated Peptides by Active Learning-Directed Coarse-Grained Molecular Simulation

Electronically active organic molecules have demonstrated great promise as novel soft materials for energy harvesting and transport. Self-assembled nanoaggregates formed from π-conjugated oligopeptides composed of an aromatic core flanked by oligopeptide wings offer emergent optoelectronic properties within a water-soluble and biocompatible substrate. Nanoaggregate properties can be controlled by tuning core chemistry and peptide composition, but the sequence-structure-function relations remain poorly characterized. In this work, we employ coarse-grained molecular dynamics simulations within an active learning protocol employing deep representational learning and Bayesian optimization to efficiently identify molecules capable of assembling pseudo-1D nanoaggregates with good stacking of the electronically active π-cores. We consider the DXXX-OPV3-XXXD oligopeptide family, where D is an Asp residue and OPV3 is an oligophenylenevinylene oligomer (1,4-distyrylbenzene), to identify the top performing XXX tripeptides within all 20³ = 8000 possible sequences. By direct simulation of only 2.3% of this space, we identify molecules predicted to exhibit superior assembly relative to those reported in prior work. Spectral clustering of the top candidates reveals new design rules governing assembly. This work establishes new understanding of DXXX-OPV3-XXXD assembly, identifies promising new candidates for experimental testing, and presents a computational design platform that can be generically extended to other peptide-based and peptide-like systems.

The Role of Hydrophobicity in the Stability and pH-Switchability of (RXDX)4 and Coumarin-(RXDX)4 Conjugate β-Sheets

pH-Switchable, self-assembling materials are of interest in biological imaging and sensing applications. Here we propose that combining the pH-switchability of RXDX (X = Ala, Val, Leu, Ile, Phe) peptides and the optical properties of coumarin creates an ideal candidate for these materials. This suggestion is tested with a thorough set of all-atom molecular dynamics simulations. We first investigate the dependence of pH-switchabiliy on the identity of the hydrophobic residue, X, in the bare (RXDX)₄ systems. Increasing the hydrophobicity stabilizes the fiber which, in turn, reduces the pH-switchabilty of the system. This behavior is found to be somewhat transferable to systems in which a single hydrophobic residue is replaced with a coumarin containing amino acid. In this case, conjugates with X = Ala are found to be unstable at both pHs, while conjugates with X = Val, Leu, Ile, and Phe are found to form stable β-sheets at least at neutral pH. The coumarin-(RFDF)₄ conjugate is found to have the largest relative entropy value of 0.884 ± 0.001 between neutral and acidic coumarin ordering distributions. Thus, we posit that coumarin-(RFDF)₄ containing peptide sequences are ideal candidates for pH-sensing bioelectronic materials.

Revealing the Sequence-Structure-Electronic Property Relation of Self-Assembling π-Conjugated Oligopeptides by Molecular and Quantum Mechanical Modeling

Self-assembled nanoaggregates of π-conjugated synthetic peptides present a biocompatible and highly tunable alternative to silicon-based optical and electronic materials. Understanding the relationship between structural morphology and electronic properties of these assemblies is critical for understanding and controlling their mechanical, optical, and electronic responses. In this work, we combine all-atom classical molecular simulations with quantum mechanical electronic structure calculations to ascertain the sequence-structure-electronic property relationship within a family of Asp-X-X-quaterthiophene-X-X-Asp (DXX-OT4-XXD) oligopeptides in which X is one of the five amino acids {Ala, Phe, Gly, Ile, Val} ({A, F, G, I, V}). Molecular dynamics simulations reveal that smaller amino acid substituents (A, G) favor linear stacking within a peptide dimer, whereas larger groups (F, I, V) induce larger twist angles between the peptides. Density functional theory calculations on the dimer show the absorption spectrum to be dominated by transitions between carbon and sulfur p orbitals. Although the absorption spectrum is largely insensitive to the relative twist angle, the highest occupied molecular orbital strongly localizes onto one molecule within the dimer at large twist angles, impeding the efficiency of transport between molecules. Our results provide a fundamental understanding of the relation between peptide orientation and electronic structure and offer design precepts for rational engineering of these systems.

Mainstream Ammonium Recovery to Advance Sustainable Urban Wastewater Management

Throughout the 20th century, the prevailing approach toward nitrogen management in municipal wastewater treatment was to remove ammonium by transforming it into dinitrogen (N₂) using biological processes such as conventional activated sludge. While this has been a very successful strategy for safeguarding human health and protecting aquatic ecosystems, the conversion of ammonium into its elemental form is incompatible with the developing circular economy of the 21st century. Equally important, the activated sludge process and other emerging ammonium removal pathways have several environmental and technological limitations. Here, we assess that the theoretical energy embedded in ammonium in domestic wastewater represents roughly 38-48% of the embedded chemical energy available in the whole of the discharged bodily waste. The current routes for ammonium removal not only neglect the energy embedded in ammonium, but they can also produce N₂O, a very strong greenhouse gas, with such emissions comprising the equivalent of 14-26% of the overall carbon footprint of wastewater treatment plants. N₂O emissions often exceed the carbon emissions related to the electricity consumption for the process requirements of WWTPs. Considering these limitations, there is a need to develop alternative ammonium management approaches that center around recovery of ammonium from domestic wastewater rather than deal with its "destruction" into elemental dinitrogen. Current ammonium recovery techniques are applicable only at orders of magnitude above domestic wastewater strength, and so new techniques based on physicochemical adsorption are of particular interest. A new pathway is proposed that allows for mainstream ammonium recovery from wastewater based on physicochemical adsorption through development of polymer-based adsorbents. Provided adequate adsorbents corresponding to characteristics outlined in this paper are designed and brought to industrial production, this adsorption-based approach opens perspectives for mainstream continuous adsorption coupled with side-stream recovery of ammonium with minimal chemical requirements. This proposed pathway can bring forward an effective resource-oriented approach to upgrade the fate of ammonium in urban water management without generating hidden externalized environmental costs.

The Effect of Acceptor Structure on Emission Color Tuning in Organic Semiconductors with D-π-A-π-D Structures

A series of novel donor-acceptor D-π-A-π-D compounds were synthesized and characterized in order to determine the influence of different acceptor units on their properties. The introduction of acceptor moieties had a direct impact on the HOMO and LUMO energy levels. Fluorescence spectra of compounds can be changed by the choice of an appropriate acceptor and were shifted from the green to the near-infrared part of spectra. Due to observed concentration induced emission quenching, the green exciplex type host was used to evaluate the potential of synthesized molecules as emitters in organic light emitting diodes (OLEDs).

A direct comparison of monomeric vs. dimeric and non-annulated vs. N-annulated perylene diimide electron acceptors for organic photovoltaics

A systematic structure–property-function evaluation of four structurally related organic photoactive materials based on the perylene diimide chromophore.

Experimental and theoretical investigations on the optical and electrochemical properties of π-conjugated donor-acceptor-donor (DAD) compounds toward a universal model

A series of nine (9) donor-acceptor-donor (DAD) π-conjugated small molecules were synthesized via palladium catalyzed Stille aromatic cross-coupling reactions by the combination of six (6) heterocycle building blocks (thiophene, furan, thiazole, 2,1,3-benzothiadiazole, 2,1,3-pyridinothiadiazole, thienothiadiazole) acting as electron donating (thiazole, furan, thiophene) and electron deficient (benzothiadiazole, pyridinethiadiazole, thienothiadiazole) units. These model compounds enable determining the correspondence between the theoretical and experimental optical and electrochemical properties for the first time, via Density Functional Theory (DFT), time-dependent DFT, UV-Vis spectroscopy, and cyclic voltammetry, accordingly. The obtained theoretical models can be utilized for the design and synthesis of new DAD structures with precise optical bandgaps, absorption maxima, and energy levels suitable for different optoelectronic applications.

Advantageous Microwave-Assisted Suzuki Polycondensation for the Synthesis of Aniline-Fluorene Alternate Copolymers as Molecular Model with Solvent Sensing Properties

Polymerization via Suzuki coupling under microwave (µW) irradiation has been studied for the synthesis of poly{1,4-(2/3-aminobenzene)-alt-2,7-(9,9-dihexylfluorene)} (PAF), chosen as molecular model. Briefly, µW-assisted procedures accelerated by two orders of magnitude the time required when using classical polymerization processes, and the production yield was increased (>95%). In contrast, although the sizes of the polymers that were obtained by non-conventional heating reactions were reproducible and adequate for most applications, with this methodology the molecular weight of final polymers were not increased with respect to conventional heating. Asymmetric orientation of the amine group within the monomer and the assignments of each dyad or regioregularity, whose values ranged from 38% to 95% with this molecule, were analysed using common NMR spectroscopic data. Additionally, the synthesis of a new cationic polyelectrolyte, poly{1,4-(2/3-aminobenzene)-co-alt-2,7-[9,9´-bis(6''-N,N,N-trimethylammonium-hexyl)fluorene]} dibromide (PAFAm), from poly{1,4-(2/3-aminobenzene)-co-alt-2,7-[9,9´-bis(6''-bromohexyl)fluorene]} (PAFBr) by using previously optimized conditions for µW-assisted heating procedures was reported. Finally, the characterization of the final products from these batches showed unkown interesting solvatochromic properties of the PAF molecule. The study of the solvatochromism phenomena, which was investigated as a function of the polarity of the solvents, showed a well-defined Lippert correlation, indicating that the emission shift observed in PAF might be due to its interaction with surrounding environment. Proven high sensitivity to changes of its environment makes PAF a promising candidate of sensing applications.

Effect of donor to acceptor ratio on electrochemical and spectroscopic properties of oligoalkylthiophene 1,3,4-oxadiazole derivatives

A structure-property study across a series of donor-acceptor-donor structures composed of mono- and bi-(1,3,4-oxadiazole) units symmetrically substituted with alkyl functionalized bi-, ter- and quaterthiophene segments is presented. Synthetically tailoring the ratio of electron-withdrawing 1,3,4-oxadiazole to electron-releasing thiophene units and their alkyl grafting pattern permitted us to scrutinize the impact of these structural factors on the redox, absorptive and emissive properties of these push-pull molecules. Contrasting trends of redox potentials were observed, with the oxidation potential closely following the donor-to-acceptor ratio, whereas the reduction potential being tuned independently by either the number of acceptor units or the conjugation length of the donor-acceptor system. Increasing the thiophene unit contribution delivered a shift from blue to green luminescence, while the structural rigidity afforded by intramolecular non-covalent interactions between 1,3,4-oxadiazole and the thiophene moieties has been identified as the prime factor determining the emission efficiency of these molecules. All six structures investigated electro-polymerize easily, yielding electroactive and electrochromic polymers. The polymer doping process is largely influenced by the length of the oligothiophene repeating unit and the alkyl chain grafting density. Polymers with relatively short oligothiophene segments are able to support polarons and polaron-pairs, whereas those with segments longer than six thiophene units could also stabilize diamagnetic charge carries - bipolarons. Increasing the alkyl chain grafting density improved the reversibility and broadened the working potential window of the p-doping process. Stable radical anions have also been investigated, bringing detailed information about the conjugation pattern of these electron-surplus species. This study delivers interesting clues towards the conscious structural design of bespoke frontier energy level oligothiophene functional materials and their polymers by incorporating a structurally matching 1,3,4-oxadiazole unit.

A naphthodithieno[3,2-b]thiophene-based copolymer as a novel third component in ternary polymer solar cells with a simultaneously enhanced open circuit voltage, short circuit current and fill factor

Ternary polymer solar cells with simultaneously improved V_OC, J_SC and FF have been achieved by doping PV12 as a third component.

Two-acceptor one-donor random terpolymers comprising thiophene- and phenyl-capped diketopyrrolopyrrole for organic photovoltaics

A series of random terpolymers comprising two electron deficient phenyl (PDPP) and thiophene (ThDPP)-capped diketopyrrolopyrrole (DPP) in conjugation with the electron-donating thiophene moiety are synthesised using Stille coupling.

Synthesis of Dithienocyclohexanones (DTCHs) as a Family of Building Blocks for π-Conjugated Compounds in Organic Electronics

The development and widespread application of organic electronic devices require the availability of simple and cost-effective suitable materials. In this study, the preparation of a new class of conjugated compounds on the basis of a dithienocyclohexanone (DTCH) core is reported. Several synthetic strategies for the preparation of dialkyl DTCH derivatives are explored, with special emphasis on the establishment of a sustainable synthetic access. Two successful synthetic pathways, both consisting of five steps, are identified: the first one featuring readily available 3-thiophenecarboxaldeyde and the second one 3-ethynylthiophene as the starting materials. Both procedures are characterized by reasonably high overall yields (over 30%) and remarkably low E factors (<400). Preliminary evidences of the use of such building blocks in the micellar Suzuki-Miyaura cross-coupling reactions leading to promising molecular semiconductors are also given. Moreover, on a small molecule containing DTCH moiety, solar cell performance was investigated.

Effect of carbon hybridization in 9H-fluorene unit on the photovoltaic properties of different fluorene-based conjugated polymers

To investigate the effect of different carbon hybridization in 9H-fluorene on the resultant polymers, a series of donor–acceptor conjugated polymers have been synthesized by copolymerizing substituted 9H-fluorenes with triazoloquinoxaline. All polymers exhibit good solution-processability and broad absorption in 350–1000 nm region with narrow optical bandgaps ranging from 1.27 eV to 1.55 eV. The results indicate that fluorene functionalization via different carbon hybridization on 9-position could be an effective strategy to fine-tune the absorption, energy levels, and photovoltaic performance of the polymers. 9-Position sp2-hybridized carbon in fluorene could enhance absorption of ultraviolet-visible and form good morphology of blending layers, through its planar rigid structure. All polymer solar cells devices exhibited moderate performance with the best power conversion efficiency of 3.02% achieved based on P2. Compared to ladder-type multifused fluorene, carbon-hybridized 9H-fluorene units can be a very useful building block for constructing narrow bandgap polymers with facile synthesis, and even interesting optoelectronic properties.

Recent Advances in Wide-Bandgap Photovoltaic Polymers

The past decade has witnessed significant advances in the field of organic solar cells (OSCs). Ongoing improvements in the power conversion efficiency of OSCs have been achieved, which were mainly attributed to the design and synthesis of novel conjugated polymers with different architectures and functional moieties. Among various conjugated polymers, the development of wide-bandgap (WBG) polymers has received less attention than that of low-bandgap and medium-bandgap polymers. Here, we briefly summarize recent advances in WBG polymers and their applications in organic photovoltaic (PV) devices, such as tandem, ternary, and non-fullerene solar cells. Addtionally, we also dissuss the application of high open-circuit voltage tandem solar cells in PV-driven electrochemical water dissociation. We mainly focus on the molecular design strategies, the structure-property correlations, and the photovoltaic performance of these WBG polymers. Finally, we extract empirical regularities and provide invigorating perspectives on the future development of WBG photovoltaic materials.

Control of the hierarchical assembly of π-conjugated optoelectronic peptides by pH and flow

Coarse-grained molecular simulations reveal the influence of pH and flow on the self-assembly of DFAG-OPV3-GAFD optoelectronic peptides.