Search

We investigate the charge-generation processes limiting the performance of low-offset organic bulk-heterojunction solar cells by studying a series of newly synthesized PBDB-T-derivative donor polymers whose ionisation energy (IE) is tuned via functional group (difluorination or cyanation) and backbone (thiophene or selenophene bridge) modifications. When blended with the acceptor Y6, the series present heterojunction donor-acceptor IE offsets ( ΔE IE ) ranging from 0.22 to 0.59 eV. As expected, small ΔE IE decrease nonradiative voltage losses but severely suppresses photocurrent generation. We explore the origin of this reduced charge-generation efficiency at low ΔE IE through a combination of opto-electronic and spectroscopic measurements and molecular and device-level modeling. We find that, in addition to the expected decrease in local exciton dissociation efficiency, reducing ΔE IE also strongly reduces the charge transfer (CT) state dissociation efficiency, demonstrating that poor CT-state dissociation can limit the performance of low-offset heterojunction solar cells., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The synthesis and applications of ring-opening metathesis polymerization (ROMP) derived poly(olefins) have emerged as an exciting area of great interest in the field of biomaterials science. The major focus of this mini-review is to present recent advances in the synthesis of functional materials using ROMP-derived poly(olefins) utilized for drug release, sensing, and cellular uptake in the past seven years (2015-2022). This review reveals that materials synthesized by ROMP-derived well-defined functional poly(olefins) stand to be highly promising systems for medical as well as biological studies. Thus, this review may prove to be beneficial for the design and development of new smart and flexible-functionality ROMP-based polymeric materials for various biological applications., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The energy required to heat, cool, and illuminate buildings continues to increase with growing urbanization, engendering a substantial global carbon footprint for the built environment. Passive modulation of the solar heat gain of buildings through the design of spectrally selective thermochromic fenestration elements holds promise for substantially alleviating energy consumed for climate control and lighting. The binary vanadium(IV) oxide VO 2 manifests a robust metal-insulator transition that brings about a pronounced modulation of its near-infrared transmittance in response to thermal activation. As such, VO 2 nanocrystals are potentially useful as the active elements of transparent thermochromic films and coatings. Practical applications in retrofitting existing buildings requires the design of workflows to embed thermochromic fillers within industrially viable resins. Here, we describe the dispersion of VO 2 nanocrystals within a polyvinyl butyral laminate commonly used in the laminated glass industry as a result of its high optical clarity, toughness, ductility, and strong adhesion to glass. To form high-optical-clarity nanocomposite films, VO 2 nanocrystals are encased in a silica shell and functionalized with 3-methacryloxypropyltrimethoxysilane, enabling excellent dispersion of the nanocrystals in PVB through the formation of siloxane linkages and miscibility of the methacrylate group with the random copolymer. Encapsulation, functionalization, and dispersion of the core-shell VO 2 @SiO 2 nanocrystals mitigates both Mie scattering and light scattering from refractive index discontinuities. The nanocomposite laminates exhibit a 22.3% modulation of NIR transmittance with the functionalizing moiety engendering a 77% increase of visible light transmittance as compared to unfunctionalized core-shell particles. The functionalization scheme and workflow demonstrated, here, illustrates a viable approach for integrating thermochromic functionality within laminated glass used for retrofitting buildings., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Novel methods to synthesize electron-deficient π-conjugated polymers utilizing transition-metal-free coupling reactions for the use of nonfunctionalized monomers are attractive due to their improved atom economy and environmental prospective. Herein we describe the use of i PrMgCl·LiCl complex to afford thiazole-based conjugated polymers in the absence of any transition metal catalyst, that enables access to well-defined polymers with good molecular weights. The mechanistically distinct polymerizations proceeded via nucleophilic aromatic substitution (S N Ar) reaction supported by density functional theory (DFT) calculations. This work demonstrates the first example of fully conjugated thiazole-based aromatic homopolymers without the need of any transition metal catalyst.

An extensive polycyclic π-system with 23 fused rings is synthesized via a highly efficient borylation reaction, in which four B-N covalent bonds and four B←N coordinate bonds are formed in one pot. B←N coordinate bonds not only lock the backbone into a near-coplanar conformation but also decrease the LUMO energy level to around -3.82 eV, demonstrating the dual utility of this strategy for the synthesis of extensive rigid polycyclic molecules and the development of n -type conjugated materials for organic electronics and organic photovoltaics.

Polyaniline derivatives represent one of the most widely used classes of conductive polymers. The fundamentally important electronic properties of pernigraniline salts, the fully oxidized and acid-doped derivatives of polyanilines, however, are still not well-understood due to their poor stability and configurational uncertainty. To address these issues and to synthetically access stable analogues of pernigraniline salts, ladder-type constitution was imparted into a series of model oligomer analogues with rigid backbones constituted by up to 27 fused rings. The syntheses were achieved through iterative cross-coupling reactions followed by cyclization and oxidation. In contrast to their unstable non-ladder-type counterparts, these ladder-type pernigraniline-like molecules all adopt a well-defined all- trans configuration and demonstrate an excellent chemical stability after protonation, rendering it possible to reveal the intrinsic electronic and magnetic properties of molecules resembling pernigraniline. Protonated salts of these oligomers feature a significant diradicaloid open-shell resonance contribution. A dominant temperature-independent Pauli paramagnetism was observed in the solid state, an indication of the delocalization nature of the polarons in ladder-type analogues of pernigraniline salt.

Carbon monoxide (CO) is an important biological gasotransmitter in living cells. Precise spatial and temporal control over release of CO is a major requirement for clinical application. To date, the most reported carbon monoxide releasing materials use expensive fabrication methods and require harmful and poorly designed tissue-penetrating UV irradiation to initiate the CO release precisely at infected sites. Herein, we report the first example of utilizing a green light-responsive CO-releasing polymer P synthesized via ring-opening metathesis polymerization. Both monomer M and polymer P were very stable under dark conditions and CO release was effectively triggered using minimal power and low energy wavelength irradiation (550 nm, ≤28 mW). Time-dependent density functional theory (TD-DFT) calculations were carried out to simulate the electronic transition and insight into the nature of the excitations for both L and M . TD-DFT calculations indicate that the absorption peak of M is mainly due to the excitation of the seventh singlet excited state, S7. Furthermore, stretchable materials using polytetrafluoroethylene (PTFE) strips based on P were fabricated to afford P-PTFE, which can be used as a simple, inexpensive, and portable CO storage bandage. Insignificant cytotoxicity as well as cell permeability was found for M and P against human embryonic kidney cells.

Directed alignment of polymer chains plays an indispensable role in charge transport properties. We focus not only on a specific method to induce the alignment but also on the design of a liquid crystalline (LC) conjugated polymer to take advantage of an intrinsic self-assembly characteristic. We synthesized a lyotropic LC conjugated polymer, CP1-P, having o -nitrobenzyl (ONB) esters as photocleavable side chains and adopted a floating film transfer method to induce the polymer chain alignment through a lyotropic LC phase transition. An optimum amount of a high boiling point solvent (1,2-dichlorobenzene) in chloroform turned out to be an important factor to maximize the polymer chain alignment. The hole transport mobility along the polymer chain alignment direction was 13-14 times higher than that in the direction perpendicular to the alignment. In addition, the removal of side chains resulted in the solvent resistivity while maintaining the alignment feature in organic thin-film transistors., Competing Interests: The authors declare no competing financial interest.

Recent advances in flexible and stretchable electronics (FSE), a technology diverging from the conventional rigid silicon technology, have stimulated fundamental scientific and technological research efforts. FSE aims at enabling disruptive applications such as flexible displays, wearable sensors, printed RFID tags on packaging, electronics on skin/organs, and Internet-of-things as well as possibly reducing the cost of electronic device fabrication. Thus, the key materials components of electronics, the semiconductor, the dielectric, and the conductor as well as the passive (substrate, planarization, passivation, and encapsulation layers) must exhibit electrical performance and mechanical properties compatible with FSE components and products. In this review, we summarize and analyze recent advances in materials concepts as well as in thin-film fabrication techniques for high- k (or high-capacitance) gate dielectrics when integrated with FSE-compatible semiconductors such as organics, metal oxides, quantum dot arrays, carbon nanotubes, graphene, and other 2D semiconductors. Since thin-film transistors (TFTs) are the key enablers of FSE devices, we discuss TFT structures and operation mechanisms after a discussion on the needs and general requirements of gate dielectrics. Also, the advantages of high- k dielectrics over low- k ones in TFT applications were elaborated. Next, after presenting the design and properties of high- k polymers and inorganic, electrolyte, and hybrid dielectric families, we focus on the most important fabrication methodologies for their deposition as TFT gate dielectric thin films. Furthermore, we provide a detailed summary of recent progress in performance of FSE TFTs based on these high- k dielectrics, focusing primarily on emerging semiconductor types. Finally, we conclude with an outlook and challenges section.

Singlet exciton fission is a spin-allowed process to generate two triplet excitons from a single absorbed photon. This phenomenon offers great potential in organic photovoltaics, but the mechanism remains poorly understood. Most reports to date have addressed intermolecular fission within small-molecular crystals. However, through appropriate chemical design chromophores capable of intramolecular fission can also be produced. Here we directly observe sub-100 fs activated singlet fission in a semiconducting poly(thienylenevinylene). We demonstrate that fission proceeds directly from the initial 1Bu exciton, contrary to current models that involve the lower-lying 2Ag exciton. In solution, the generated triplet pairs rapidly recombine and decay through the 2Ag state. In films, exciton diffusion breaks this symmetry and we observe long-lived triplets which form charge-transfer states in photovoltaic blends.

We study the molecular order and morphology in poly(3-hexylthiophene) (P3HT) and poly(3-hexylselenophene) (P3HS) thin films and their blends with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM). We find that substitution of the sulfur atoms in the thiophene rings of P3HT by heavy selenium atoms increases the tendency of the molecules to form better ordered phase; interestingly, their overall fraction of ordered phase is much lower than that of P3HT-based films. The higher tendency of P3HS molecules to order (aggregate) is consistent with more planar chain conformation simulated. The lower fraction of ordered phase (or the higher fraction of disordered phase) in P3HS-based films is clearly identified by in-plane skeleton Raman modes under resonant excitation conditions, such as a smaller ratio of the C═C modes associated with the ordered (∼1422 cm(-1)) and disordered (∼1446 cm(-1)) phases (I(1422 cm(-1))/I(1446 cm(-1)) = 1.4 for P3HS and 0.6 for P3HS:PCBM), compared with P3HT-based films (I(1449 cm(-1))/I(1470 cm(-1)) = 2.5 for P3HT and 1.0 for P3HT:PCBM) and a larger Raman dispersion of the C═C mode: P3HS (17 cm(-1)) versus P3HT (6 cm(-1)) and P3HS:PCBM (36 cm(-1)) versus P3HT:PCBM films (23 cm(-1)). The higher fraction of disordered phase in P3HS prevents the formation of micrometer-sized PCBM aggregates in blend films during thermal annealing. Importantly, this lower fraction but better quality of ordered phase in P3HS molecules strongly influences P3HS:PCBM photovoltaic performance, producing smaller short-circuit current (J(sc)) in pristine devices, but significantly larger increase in J(sc) after annealing compared to P3HT:PCBM devices. Our results clarify the effects of heavy atom substitution in low band gap polymers and their impact on blend morphology and device performance. Furthermore, our study clearly demonstrates resonant Raman spectroscopy as a simple, but powerful, structural probe which provides important information about "fraction/quantity of ordered phase" of molecules, not easily accessible using traditional X-ray-based techniques.

The improvement of the power conversion efficiency (PCE) of polymer bulk heterojunction (BHJ) solar cells has generally been achieved through synthetic design to control frontier molecular orbital energies and molecular ordering of the electron-donating polymer. An alternate approach to control the PCE of a BHJ is to tune the miscibility of the fullerene and a semiconducting polymer by varying the structure of the fullerene. The miscibility of a series of 1,4-fullerene adducts in the semiconducting polymer, poly(3-hexylselenophene), P3HS, was measured by dynamic secondary ion mass spectrometry using a model bilayer structure. The microstructure of the bilayer was investigated using high-angle annular dark-field scanning transmission microscopy and linked to the polymer-fullerene miscibility. Finally, P3HS:fullerene BHJ solar cells were fabricated from each fullerene derivative, enabling the correlation of the active layer microstructure to the charge collection efficiency and resulting PCE of each system. The volume fraction of polymer-rich, fullerene-rich, and polymer-fullerene mixed domains can be tuned using the miscibility leading to improvement in the charge collection efficiency and PCE in P3HS:fullerene BHJ solar cells. These results suggest a rational approach to the design of fullerenes for improved BHJ solar cells.

The synthesis of a novel electron-deficient fused pyrrolo[3,2-d:4,5-d']bisthiazole is reported from 2-bromothiazole. This was copolymerized with thiophene, selenophene, thienothiophene, and bithiophene by microwave-assisted Stille polycondensation. The resulting polymers exhibited small optical band gaps combined with low-lying HOMO energy levels and demonstrated semiconducting behavior in organic field effect transistors.