The PCPDTBT Family: Correlations between Chemical Structure, Polymorphism, and Device Performance

Multifunctional Near Infrared Polymer Dots for Enhanced Synergistic Photodynamic/Photothermal Effect In Vitro

Synergistic photodynamic/photothermal therapy (PDT/PTT) can be used to target cancer cells by locally generating singlet oxygen species or increasing temperature under laser irradiation. This approach offers higher tumor ablation efficiency, lower therapeutic dose requirements, and reduced side effects compared to single treatment approaches. However, the therapeutic efficiency of PDT/PTT is still limited by the low oxygen levels within the solid tumors caused by abnormal vasculature and altered cancer cell metabolism. To address these challenges, we developed multifunctional nanoparticles with high catalytic activity for converting tumor hydrogen peroxide (H2O2) into oxygen (O2). Using poly(styrene-co-maleic anhydride) (PSMA) as a cross-linker, we generated compact, highly fluorescent Pdots, used poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) as a near-infrared photosensitizer for both photodynamic and photothermal applications, and incorporated manganese (Mn) ions to catalyze the H2O2-to-O2 conversion. These Mn-doped Pdots significantly enhance O2 production, achieving an enhanced 1O2 quantum yield from 0.46 to 0.64 with the addition of H2O2, achieving the goal of improving PDT efficiency. With this rational design, we produced Pdots with enhanced H2O2-to-1O2 converting ability for potential use in PDT. For photothermal applications, our Pdots generate a photothermal conversion efficiency of 53%. In vitro studies using human MCF7 adenocarcinoma cells confirmed the biocompatibility of these Pdots in the absence of laser exposure with a pronounced cell killing effect under laser irradiation for synergistic PDT/PTT. These results highlight the promise of Pdots in overcoming oxygen limitations, balancing the performance of PDT/PTT, and enhancing the therapeutic efficacy of PDT/PTT in cancer cells in vitro.

Recent Advances in Polymorphism of Organic Solar Cells

As organic solar cells (OSCs) achieve notable advancements, a significant consensus has been highlighted that the device performance is intricately linked to the active layer morphology. With conjugated molecules being widely employed, intermolecular interactions exert substantial influence over the aggregation state and morphology formation, resulting in distinct molecular packing motifs, also known as polymorphism. This phenomenon is closely associated with processing conditions and exerts a profound impact on functional properties. Consequently, understanding the mechanisms underlying polymorphism formation and establishing a definitive correlation between polymorphism and photophysical behavior is crucial for driving high-performance OSCs. In this review, a comprehensive synthesis of recent developments is provided and emphasizing its pivotal role in the field of OSC polymorphism. The thermodynamic and kinetic principles governing polymorphism formation are examined. Then, representative polymorphisms are classified in OSC materials, segmenting them into homopolymers, copolymers, and IDTT- and BTP-based small molecules. Additionally, prevalent strategies are evaluated for manipulating polymorphism. This review culminates with an analysis of the critical effects of polymorphism on OSCs, including charge carrier characteristics, photovoltaic efficiency, and long-term stability. By offering novel perspectives and practical insights, this work seeks to guide future efforts in the morphological optimization of high-efficiency OSCs.

Accurate Determination of the Uniaxial Complex Refractive Index and the Optical Band Gap of Polymer Thin Films to Correlate Their Absorption Strength and Onset of Absorption

The advanced development of optoelectronic devices requires a methodical knowledge of the fundamental material properties of the key active components. Systematic investigations and correlations of such basic optical properties can lead to new insights for the design of more potent materials. In this perspective, we provide a systematic overview of the uniaxial anisotropic complex refractive indices and the absorption coefficients obtained by ellipsometry as well as the optical band gap energies derived from Tauc plots of six selected solution-processed polymer thin films. While the optical band gap energies are intentionally distributed over the visible spectral range, we found that the absorption strength of all polymer samples are grouped in a random distribution within a rather uniform range of values.

Perpendicular crossing chains enable high mobility in a noncrystalline conjugated polymer

The nature of interchain π-system contacts, and their relationship to hole transport, are elucidated for the high-mobility, noncrystalline conjugated polymer C16-IDTBT by the application of scanning tunneling microscopy, molecular dynamics, and quantum chemical calculations. The microstructure is shown to favor an unusual packing motif in which paired chains cross-over one another at near-perpendicular angles. By linking to mesoscale microstructural features, revealed by coarse-grained molecular dynamics and previous studies, and performing simulations of charge transport, it is demonstrated that the high mobility of C16-IDTBT can be explained by the promotion of a highly interconnected transport network, stemming from the adoption of perpendicular contacts at the nanoscale, in combination with fast intrachain transport.

Effect of Chemical Modification on Molecular Ordering in Polydiketopyrrolopyrrole Copolymers: From Liquid Crystalline to Crystalline

The chemical architecture of conjugated polymers is often designed by contemplating and understanding the consequences of structural changes on electronic properties at the molecular level. However, even minor changes to the chemical structure of a polymer can significantly influence the packing arrangement, which also influences the electronic properties of the bulk material. Here, we investigate the molecular arrangement in the ordered state at room temperature of a series of three different polydiketopyrrolopyrroles (PDPPs) in bulk and oriented thin films in detail by wide-angle X-ray scattering and by atomic force microscopy. The changes in the chemical structure of the investigated PDPPs, namely, an additional side chain or a different flanking unit, lead to an increase in long-range order and thereby to a change in the phase state from sanidic ordered via sanidic rectangular or oblique to crystalline.

Enhanced organic photovoltaic-based retinal prosthesis using a cathode-modified structure with plasmonic silver nanoparticles: a computational study

Introduction

Organic interfaces have recently emerged as a breakthrough trend in biomedical applications, demonstrating exceptional performance in stimulating retinal neuronal cells owing to their high flexibility and compatibility with tissues. However, the primary challenge associated with organic photovoltaics is their low efficiency compared to that of their inorganic counterparts. Among different approaches, embedding plasmonic metal nanoparticles (NPs) in active or buffer layers can efficiently improve photovoltaic cell performance.

Methods

A cathode decorated with silver nanoparticles is introduced to increase the absorption Phenomenon and improve the interface performance as a computational study. In addition to embedding spherical silver nanoparticles in the active layer (A-AgNPs), a monolayer array of spherical AgNPs in the cathode electrode (K-AgNPs) is incorporated. In this configuration, the large K-AgNPs play dual roles: acting as cathode electrode and serving as plasmonic centers to increase light trapping and absorption. The bulk heterojunction PCPDTBT:PCBM is chosen as the active layer due to its favorable electronic properties.

Results

Our computational analysis demonstrates a notable 10% enhancement in the photovoltaic cell current density for the developed structure with K-AgNPs in contrast to without them. Additionally, the simulation results reveal that the modeled device achieves a two-fold efficiency of the bare photovoltaic cell (without A-AgNPs and K-AgNPs), which is particularly evident at a low intensity of 0.26 mW/mm2.

Discussion

This study aims to propose an efficient epiretinal prosthesis structure using a different strategy for plasmonic effects rather than conventional methods, such as incorporating NPs into the active or buffer layer. This structure can prevent the harmful side effects of using large metal NPs (r > 10 nm) in the active layer during exciton quenching, charge trapping, and recombination, which deteriorate the power conversion efficiency (PCE).

Crystallization of D-A Conjugated Polymers: A Review of Recent Research

D-A conjugated polymers are key materials for organic solar cells and organic thin-film transistors, and their film structure is one of the most important factors in determining device performance. The formation of film structure largely depends on the crystallization process, but the crystallization of D-A conjugated polymers is not well understood. In this review, we attempted to achieve a clearer understanding of the crystallization of D-A conjugated polymers. We first summarized the features of D-A conjugated polymers, which can affect their crystallization process. Then, the crystallization process of D-A conjugated polymers was discussed, including the possible chain conformations in the solution as well as the nucleation and growth processes. After that, the crystal structure of D-A conjugated polymers, including the molecular orientation and polymorphism, was reviewed. We proposed that the nucleation process and the orientation of the nuclei on the substrate are critical for the crystal structure. Finally, we summarized the possible crystal morphologies of D-A conjugated polymers and explained their formation process in terms of nucleation and growth processes. This review provides fundamental knowledge on how to manipulate the crystallization process of D-A conjugated polymers to regulate their film structure.

Unraveling the Unconventional Order of a High-Mobility Indacenodithiophene-Benzothiadiazole Copolymer

A new class of donor-acceptor (D-A) copolymers found to produce high charge carrier mobilities competitive with amorphous silicon (>1 cm² V^-1 s^-1) exhibit the puzzling microstructure of substantial local order, however lacking long-range order and crystallinity previously deemed necessary for achieving high mobility. Here, we demonstrate the application of low-dose transmission electron microscopy to image and quantify the nanoscale and mesoscale organization of an archetypal D-A copolymer across areas comparable to electronic devices (≈9 μm²). The local structure is spatially resolved by mapping the backbone (001) spacing reflection, revealing nanocrystallites of aligned polymer chains throughout nearly the entire film. Analysis of the nanoscale structure of its ordered domains suggests significant short- and medium-range order and preferential grain boundary orientations. Moreover, we provide insights into the rich, interconnected mesoscale organization of this new family of D-A copolymers by analysis of the local orientational spatial autocorrelations.

Atomic Force Microscope Study of Ag-Conduct Polymer Hybrid Films: Evidence for Light-Induced Charge Separation

Scanning Kelvin probe microscopy (SKPM), electrostatic force microscopy (EFM) are used to study the microscopic processes of the photo-induced charge separation at the interface of Ag and conductive polymers, i.e., poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-bʹ]dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and poly(3-hexylthiophene-2,5-diyl) (P3HT). They are also widely used in order to directly observe the charge distribution and dynamic changes at the interfaces in nanostructures, owing to their high sensitivity. Using SKPM, it is proved that the charge of the photo-induced polymer PCPDTBT is transferred to Ag nanoparticles (NPs). The surface charge of the Ag-induced NPs is quantified while using EFM, and it is determined that the charge is injected into the polymer P3HT from the Ag NPs. We expect that this technology will provide guidance to facilitate the separation and transfer of the interfacial charges in the composite material systems and it will be applicable to various photovoltaic material systems.

Enhanced optical imaging properties of lipid nanocapsules as vehicles for fluorescent conjugated polymers

Conjugated polymer nanoparticles (CPNs) have emerged as highly photostable probes for optical and photoacoustic imaging. However, the aggregation of conjugated polymer (CP) molecules upon nanoparticle formation is associated with fluorescence quenching, poor yields and mutable particle sizes. This study investigated whether the CP encapsulation within the liquid midchain triglyceride (MCT) core of lipid nanocapsules (LNCs) may achieve reduced packing of CP chains leading to a stable system with enhanced optical features. The red- and near infrared-emitting CPs, CN-PPV and PCPDTBT, showed precipitation and aggregation-induced quenching with concentrations >~25 µg/mL in MCT alone. Despite this, CP encapsulation within LNCs abolished quenching at concentrations up to 1500 µg/mL. PCPDTBT-LNCs exhibited a quantum yield of 2.8% and a higher signal:background ratio in an optical imaging phantom compared to literature reports of PCPDTBT encapsulated in PEG-PLGA nanoparticles. In contrast, PCPDTBT-LNCs had slightly lower photoacoustic amplitudes than reported PEG-PLGA systems. CP-LNCs were also stable in size (32 ± 0.7 nm) and photoluminescence over 21 days at 4 °C, 25 °C and 37 °C. In summary, encapsulation of CP within the liquid core of lipid nanocapsules enhances the optical properties of fluorescent CP.

Charge transport in high-mobility conjugated polymers and molecular semiconductors

Conjugated polymers and molecular semiconductors are emerging as a viable semiconductor technology in industries such as displays, electronics, renewable energy, sensing and healthcare. A key enabling factor has been significant scientific progress in improving their charge transport properties and carrier mobilities, which has been made possible by a better understanding of the molecular structure-property relationships and the underpinning charge transport physics. Here we aim to present a coherent review of how we understand charge transport in these high-mobility van der Waals bonded semiconductors. Specific questions of interest include estimates for intrinsic limits to the carrier mobilities that might ultimately be achievable; a discussion of the coupling between charge and structural dynamics; the importance of molecular conformations and mesoscale structural features; how the transport physics of conjugated polymers and small molecule semiconductors are related; and how the incorporation of counterions in doped films-as used, for example, in bioelectronics and thermoelectric devices-affects the electronic structure and charge transport properties.

Efficient Debundling of Few-Walled Carbon Nanotubes by Wrapping with Donor-Acceptor Polymers for Improving Thermoelectric Properties

Organic thermoelectric (TE) materials have great potential as sustainable energy sources for powering flexible and wearable electronic devices via harvesting of human body heat. Recent advances in soluble conjugated polymer/carbon nanotube (CNT) composites have facilitated achievement of high TE power factors. However, the effects of conjugated polymers on the debundling and electrical percolation of CNTs and on the TE properties of their composites are not yet fully understood. Herein, we introduce a novel type of polymer/CNT composite composed of a donor-acceptor (D-A)-type polymer and few-walled CNTs (FWCNTs). Three kinds of D-A polymers are employed to disperse FWCNTs, and the photophysical, morphological, and TE properties of the resulting polymer/FWCNT composites are compared with those of composites composed of FWCNTs dispersed with conventional donor-only poly(3-hexylthiophene). The results reveal that the strong intermolecular interaction forces and high backbone planarity of the D-A polymers facilitate effective debundling of FWCNTs, which results in much smaller bundle sizes. Consequently, the D-A polymer/FWCNT composite films show superior electrical percolation and TE performances with improved power factors of up to 459 μW/mK². Finally, we demonstrate the feasibility of the D-A polymer/FWCNT composites for use in the fabrication of a flexible TE generator, which shows a maximum power output of 210 nW at a temperature gradient of 20 K.

Low molecular weight PEG-PLGA polymers provide a superior matrix for conjugated polymer nanoparticles in terms of physicochemical properties, biocompatibility and optical/photoacoustic performance

The near-infrared absorbing conjugated polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) has been investigated as a contrast agent for optical and photoacoustic imaging. Lipophilic π-conjugated polymers can be efficiently encapsulated within self-assembling diblock copolymer poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG-PLGA) nanoparticles, although the effect of variations in PEG and PLGA chain lengths on nanoparticle properties, performance and biocompatibility have not yet been investigated. In this study, PEG-PLGA with different block lengths (PEG_2kDa-PLGA_4kDa, PEG_2kDa-PLGA_15kDa and PEG_5kDa-PLGA_55kDa) were used to encapsulate PCPDTBT. Nanoparticle sizes were smallest (<100 nm) when using PEG_2kDa-PLGA_4kDa, with <5% PCPDTBT content and a reduction in the total solids concentration of the organic phase. All PEG-PLGA nanoparticles were colloidally stable in water and serum-supplemented cell culture medium over 24 h at 37 °C, with slight evidence of protein surface adsorption. PEG_2kDa-PLGA_4kDa systems showed a threefold lower cytotoxicity (IC₅₀ value) than the other two systems. Haemolytic activity was <2.5% for all systems and no platelet aggregation or inhibition of ADP-induced platelet aggregation was observed. Encapsulation of PCPDTBT within a PEG-PLGA matrix shifted fluorescence emission towards red wavelengths (760 nm in THF vs. 840 nm in nanoparticles) and reduced the quantum yield by 30-70-fold compared to THF. Nonetheless, PCPDTBT:PEG_2kDa-PLGA_4kDa systems had a marginally higher quantum yield and signal-to-background ratio in a phantom mouse compared with PEG_2kDa-PLGA_15kDa and PEG_5kDa-PLGA_55kDa systems. As a photoacoustic imaging probe, PCPDTBT:PEG_2kDa-PLGA_4kDa systems also showed a higher photoacoustic amplitude compared to higher molecular weight PEG-PLGA systems. Overall, the low molecular weight PEG_2kDa-PLGA_4kDa nanoparticle systems conferred the benefits of smaller sizes, reduced cytotoxicity and enhanced imaging performance compared to higher molecular weight matrix polymers.

Impact of polymorphism on the optoelectronic properties of a low-bandgap semiconducting polymer

Polymorphism of organic semiconducting materials exerts critical effects on their physical properties such as optical absorption, emission and electrical conductivity, and provides an excellent platform for investigating structure–property relations. It is, however, challenging to efficiently tune the polymorphism of conjugated polymers in aggregated, semi-crystalline phases due to their conformational freedom and anisotropic nature. Here, two distinctly different semi-crystalline polymorphs (β₁ and β₂) of a low-bandgap diketopyrrolopyrrole polymer are formed through controlling the solvent quality, as evidenced by spectroscopic, structural, thermal and charge transport studies. Compared to β₁, the β₂ polymorph exhibits a lower optical band gap, an enhanced photoluminescence, a reduced π-stacking distance, a higher hole mobility in field-effect transistors and improved photocurrent generation in polymer solar cells. The β₁ and β₂ polymorphs provide insights into the control of polymer self-organization for plastic electronics and hold potential for developing programmable ink formulations for next-generation electronic devices.

Tuning polymorphism of conjugated polymers, though a promising method for studying and controlling the structure-property relations in these materials remains a challenge. Here, the authors identify two aggregated semi-crystalline polymorphs of a low-bandgap diketopyrrolopyrrole-based polymer.

Self-Organization and Charge Transport Properties of Selenium and Tellurium Analogues of Polythiophene

A series of conjugated polymers comprising polythiophene, polyselenophene, and polytellurophene with branched 3,7-dimethyloctyl side chains, well-matched molecular weight, dispersity, and regioregularity is synthesized. The ionization potential is found to vary from 5.14 to 5.32 eV, with polytellurophene having the lowest potential. Field-effect transistors based on these materials exhibit distinct hole transport mobility that varies by nearly three orders of magnitude, with polytellurophene having the highest mobility (2.5 × 10^-2 cm² V^-1 s^-1 ). The large difference in mobility demonstrates the significant impact of heteroatom substitution. Although the series of polymers are very similar in structure, their solid-state properties are different. While the thin film microstructure of polythiophene and polyselenophene is identical, polytellurophene reveals globular features in the film topography. Polytellurophenes also appear to be the least crystalline, even though their charge transport properties are superior to other samples. The torsional barrier and degree of planarity between repeat units increase as one moves down group-16 elements. These studies show how a single atom in a polymer chain can have a substantial influence on the bulk properties of a material, and that heavy group-16 atoms have a positive influence on charge transport properties when all other variables are kept unchanged.

Introducing correlations into carrier transport simulations of disordered materials through seeded nucleation: impact on density of states, carrier mobility, and carrier statistics

Disorder in organic semiconductors has made it challenging to achieve performance gains; this is a result of the many competing and often nuanced mechanisms effecting charge transport. In this article, we attempt to illuminate one of these mechanisms in the hopes of aiding experimentalists in exceeding current performance thresholds. Using a heuristic exponential function, energetic correlation has been added to the Gaussian disorder model (GDM). The new model is grounded in the concept that energetic correlations can arise in materials without strong dipoles or dopants, but may be a result of an incomplete crystal formation process. The proposed correlation has been used to explain the exponential tail states often observed in these materials; it is also better able to capture the carrier mobility field dependence, commonly known as the Poole-Frenkel dependence, when compared to the GDM. Investigation of simulated current transients shows that the exponential tail states do not necessitate Montroll and Scher fits. Montroll and Scher fits occur in the form of two distinct power law curves that share a common constant in their exponent; they are clearly observed as linear lines when the current transient is plotted using a log-log scale. Typically, these fits have been found appropriate for describing amorphous silicon and other disordered materials which display exponential tail states. Furthermore, we observe the proposed correlation function leads to domains of energetically similar sites separated by boundaries where the site energies exhibit stochastic deviation. These boundary sites are found to be the source of the extended exponential tail states, and are responsible for high charge visitation frequency, which may be associated with the molecular turnover number and ultimately the material stability.

Small Molecules Derived from Thieno[3,4-c]pyrrole-4,6-dione (TPD) and Their Use in Solution Processed Organic Solar Cells

In this work, microwave synthesis, chemical, optical and electrochemical characterization of three small organic molecules, TPA-TPD, TPA-PT-TPD and TPA-TT-TPD with donor-acceptor structure and their use in organic photovoltaic cells are reported. For the synthesis, 5-(2-ethylhexyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione was used as electron withdrawing fragment while the triphenylamine was used as electron donating fragment. Molecular electronic geometry and electronic distribution density were established by density functional theory (DFT) calculations and confirmed by optical and chemical characterization. These molecules were employed as electron-donors in the active layer for manufacturing bulk heterojunction organic solar cells, where [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) was used as electron-acceptor. As cathode, Field's metal (FM), an eutectic alloy (Bi/In/Sn: 32.5%, 51%, and 16.5%, respectively) with a melting point above 62 °C, was easily deposited by drop casting under vacuum-free process and at air atmosphere. Prepared devices based on TPA-TPD:PC71BM (1:4 w/w ratio) presented a large VOC = 0.97 V, with JSC = 7.9 mA/cm², a FF = 0.34, then, a power conversion efficiency (PCE) of 2.6%.