Organic Semiconducting Polymer Research Articles

(Invited) Doping at the Extreme in Organic Semiconductors: Challenges and Opportunities

Molecular doping is an effective tool to enhance bulk conductivity, increase carrier injection and de-activate electron or hole traps in organic molecular and polymer semiconductors. Considerable effort has been directed toward the synthesis of powerful and stable p-type and n-type molecular dopants over the past decade.[1,2] This talk reviews a range of molecular redox agents used in organic electronics, with focus on strong reductants and oxidants for organic semiconductors with low electron affinity (EA) and large ionization energy (IE), respectively. In particular, we look at air-stable dimers, e.g. [RuCp*Mes]2, formed of 19-electron organometallic sandwich compounds able to reduce organic semiconductors with EA well below 3 eV.[3] We review powerful single-electron molecular oxidants, e.g. F6-TCNNQ and CN6-CP, which can introduce holes in organic semiconductors with IE larger than 5.6 eV. Applications of these n- and p-dopants to improve the conductivity of carrier injection layers and create large gap semiconductor p-i-n structures are described.[4] The last part of the talk focuses on recent work on adduct-based p-doping of organic semiconductors, applicable to a range of hole transport materials.[5][1]S. Barlow, S.R. Marder, X. Lin, F. Zhang and A. Kahn, Electrical Doping of Organic Semiconductors with Molecular Oxidants and Reductants, Handbook of Conducting Polymers (2019)[2] G. Song, S.B. Kim,S. Mohapatra, Y. Qi, T. Sajoto, A. Kahn, S.R. Marder, S. Barlow, n-Doping of Organic Electronic Materials Using Air-Stable Organometallics, Adv. Mat. 24, 699 (2012)[3] X. Lin, B. Wegner, K. M. Lee, M. A. Fusella, F. Zhang, K. Moudgil, B. P. Rand, S. Barlow, S. R. Marder, N. Kochand A. Kahn, Beating the Thermodynamic Limit: Photo-Activation of n-Doping in Organic Semiconductors, Nature Materials 16, 1209 (2017)[4] H. L. Smith, J. T. Dull, S. Mohapatra, S. Barlow, S. Marder, B. P. Rand, and A. Kahn, Powerful organic molecular oxidant and reductant enable a large gap, blue light-emitting organic homojunction diode, ACS Appl. Mat. Int. 14, 2381 (2022)[5] N. Sakai, R. Warren, F. Zhang, S. Nayak, S. V. Kesava, Y.-H. Lin, H. S. Biswal, X. Lin, A. Kahn, M. Riede, P. K. Nayak and H. J. Snaith, Adduct-based p-doping of Organic Semiconductors, Nature Materials, 20, 1248 (2021)

Deciphering single-cell transcriptomic landscape of tumors in colorectal cancer treated with photothermal semiconducting polymers to design the combination therapy with checkpoint blockades for inhibition of tumor progression and metastasis

Immunotherapy is often less effective for tumors with “immune-excluded,” or “immune-desert” microenvironment. To circumvent this hurdle, new therapeutic strategies need to be designed to reprogram the tumor microenvironment (TME). It is well known that photothermal therapy (PTT) can prime the TME and provoke the systemic anti-tumor immunity. But few studies perform extensive exploration in depth to decipher the changes in TME after PTT with cutting-edge technology besides conventional flow cytometry analysis. In this study, we designed a nanosystem consisting of organic semiconductor polymer liposome nanoparticles (Y8 NPs) as a multimodal imaging and photothermal agent to image and treat tumors. Upon laser irradiation, Y8 NPs in tumors could rapidly increase the temperature, induce massive cancer cell apoptosis and also promote the immunogenic cell death (ICD), ultimately remodulating the TME. We employed single cell RNA sequencing (scRNA-seq) technology to comprehensively explore transcriptomic profiling of individual cells constituting TME, demonstrating heterogenous alterations in the subtypes of immune cells, even tumor cells. Considering the findings by scRNA-seq and TME remodulation, the combinational strategy with checkpoint blockade PD-1 antibody was designed to treat the tumors, demonstrating that the combination not only impedes primary tumor progression but also produce profound abscopal anti-tumor effect. In conclusion, we provide a simple strategy for the remodulation of TME with a photothermal nanosystem to achieve activation of anti-tumor immunity, and suppress primary and metastatic tumor progression.

Synthesis and Performance of Bithiophene Isoindigo Organic Semiconductors with Side‐Chain Functionality in Transistors

The isoindigo and its derivatives have rapidly garnered attention as widely employed electron‐deficient moieties, finding extensive applications in organic field‐effect transistors. In this study, four different isoindigo‐based organic semiconductor polymers were synthesized via a Stille coupling reaction of four isoindigo molecules with varying side chains serving as acceptors and bithiophene as donors. Furthermore, their optical, electrochemical, thermal stability, and other relevant properties were comprehensively evaluated. These polymers exhibited remarkable electrochemical and thermal stability attributed to their low LUMO energy level, which facilitates effective electrical contact between the semiconductor layer and the source/drain while ensuring excellent air stability for the semiconductor polymers. Additionally, solution‐gate field‐effect transistors prepared using these polymers achieved hole mobilities of 10‐2 cm2V‐1S‐1 along with an Ion/Ioff ratio of 8.39×103, demonstrating exceptional field‐effect performance.

CRISPR/Cas12a coupled with In2O3/multiwalled carbon nanotube/PTCDA-EDA-DAP modified electrode self-powered photoelectrochemical assay for EBV-DNA

The design and engineering of photoelectroactive materials is recognized as a crucial step to regulate the performance of photoelectrochemical biosensing. Herein, an organic semiconductor polymer, PTCDA-EDA-DAP, was synthesized from perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), ethylenediamine (EDA) and 1,3-diamino-2-propanol (DAP). In2O3/multiwalled carbon nanotube/PTCDA-EDA-DAP enable a stable and unchanging photocurrent in the range from 0 V to 0.3 V and an excellent self-powered photocurrent. Based on this superior photoelectrochemical property, we fabricated an ultrasensitive photoelectrochemical assay for EBV-DNA based on CRISPR/Cas12a double cycling signal amplification. The target DNA stimulated Nt.BsmAI nicking, extension growth and a short chain nucleic acid as secondary targets being generated. The secondary target initiated next round of polymerization/cleavage. So that, after the two rounds of slicing and prolongation growth, the exponential growth dsDNA was generated resulting dsDNA bound to the Cas12a-crRNA complex, the trans-cleavage activity of Cas12a was activated, and resulted in amplified photocurrent. This photoelectrochemical assay had a LOD of 45 aM. The successful detection of EBV-DNA in serum samples demonstrated the promising application in real samples.

Development of high-performance flexible photodetectors through band engineering and synergistic modulation in P3HT/C3N5 thin film

Flexible photodetectors, with applications ranging from large-scale photosensors to flexible solar cells and fiber-optical sensors, offer a promising avenue for technological advancement. Despite their high performance and stability, conventional inorganic photodetectors suffer from complex, costly manufacturing processes and lack mechanical flexibility. This gap is potentially bridged by organic semiconducting polymers (OSPs), which require enhancements in charge transport capabilities. Integrating exfoliated graphitic carbon nitride (C3N5) with OSPs, specifically into a poly(3-hexylthiophene-2,5-diyl) (P3HT) matrix, has shown to significantly improve electrical and optoelectronic properties due to C3N5's excellent optoelectronic features, adjustable bandgap, and stability. This study successfully fabricated flexible photodetectors with a P3HT/C3N5(3 %) mix in a Schottky barrier diodes (SBDs) configuration, achieving a 100-fold increase in photocurrent, exceptional flexibility, and rapid response to light. These findings highlight the potential of a synergistic approach in developing high-performance, commercially viable flexible photodetectors.

Semiconducting Polymer Dots for Dual-Wavelength Differential Background-Suppressed Photoacoustic Imaging.

Photoacoustic imaging (PAI) can sensitively detect regions and substances with strong optical absorption, which means that diseased tissue can be imaged with high contrast in the presence of surrounding healthy tissue through the photoacoustic effect. However, its signal intensity and resolution may be limited by background signals generated by endogenous chromophores such as melanin and hemoglobin. A feasible method for practical application of this so-called background-suppressed PAI is still lacking. In this work, a dual-wavelength differential background noise-suppressed photoacoustic tomography is developed based on organic semiconducting polymer dots (Pdots). The Pdots have a strong absorption peak at 945nm, and then the absorption decreases sharply with the increase of wavelength, and the absorption intensity drops to only about a quarter of the original value at 1050nm. The present system significantly suppresses the strong background noise of blood through dual-wavelength differential PAI, enabling precise monitoring of the distribution information of theranostic agents in diseased tissues. The signal-to-noise ratio of the theranostic agent distribution map is increased by about 20dB. This work provides a platform for real-time and accurate monitoring of tumors and drugs, which helps avoid damage to healthy tissue during treatment and has clinical significance in cancer treatment.

Conformational Analysis of Conjugated Organic Materials: What Are My Heteroatoms Really Doing?

Organic semiconductor small molecules and polymers often incorporate heteroatoms into their chemical structures to affect the electronic properties of the material. A particular design philosophy has been to use these heteroatoms to influence torsional potentials, since the overlap of adjacent π-orbitals is most efficient in planar systems and is critical for charge delocalization in these systems. Since these design rules became popular, the messages from the earlier works have become lost in a sea of reports of "conformational locks", where the non-covalent interactions have relatively small contributions to planarizing torsional potentials. Greater influences can be found in the stabilization by extended conjugation, consideration of steric repulsion, and the interactions involving solubilizing chains and neighboring molecules or polymer chains in condensed phases.

Polymer-Unit Graph: Advancing Interpretability in Graph Neural Network Machine Learning for Organic Polymer Semiconductor Materials.

The graph representation of complex materials plays a crucial role in the field of inorganic and organic materials investigations for developing data-centric materials science, such as those using graph neural networks (GNNs). However, the currently prevalent GNN models are primarily employed for investigating periodic crystals and organic small molecule data, yet they still encounter challenges in terms of interpretability and computational efficiency when applied to polymer monomers and organic macromolecules data. There is still a lack of graph representation of organic polymers and macromolecules specifically tailored for GNN models to explore the structural characteristics. The Polymer-unit Graph, a novel coarse-grained graph representation method introduced in study, is dedicated to expressing and analyzing polymers and macromolecules. By incorporating the Polymer-unit Graph into the GNN models and analyzing the organic semiconductor (OSC) materials database, it becomes possible to uncover intricate structure-property relationships involving branched-chain engineering, fluoridation substitution, and donor-acceptor combination effects on the elementary structure of OSC polymers. Furthermore, the Polymer-unit Graph enables visualizing the relationship between target properties and polymer units while reducing training time by an impressive 98% and minimizing molecular graph representation models. In conclusion, the Polymer-unit Graph successfully integrates the concept of Polymer-unit into the field of GNNs, enabling more accurate analysis and understanding of organic polymers and macromolecules.

Controlling Nonradiative Recombination in an Organic Semiconducting Polymer Donor–Acceptor System Using Organometallic Phosphors

Controlling Nonradiative Recombination in an Organic Semiconducting Polymer Donor–Acceptor System Using Organometallic Phosphors

Benchmarking DFT and Supervised Machine Learning: An Organic Semiconducting Polymer Investigation.

Using a training set consisting of twenty-two well-known semiconducting organic polymers, we studied the ability of a simple linear regression supervised machine learning algorithm to accurately predict the bandgap (BG) and ionization potential (IP) of new polymers. We show that using the PBE or PW91 exchange-correlation functionals and this simple linear regression, calculated BGs and IPs can be obtained with average percent errors of less than 3 and 4%, respectively. We then apply this method to predict the BG and IP of a group of new polymers composed of monomers used in the training set and their derivatives in AABB and ABAB orientations.

Importance of Short-Range Order in Governing Thin Film Morphology and Electronic Properties of Polymeric Organic Semiconductors

Importance of Short-Range Order in Governing Thin Film Morphology and Electronic Properties of Polymeric Organic Semiconductors

Performance-enhanced intrinsic polarization-sensitive organic photodetectors by molecular interaction modulation

Polarization-sensitive organic photodetectors (OPDs) are increasingly paid attention for their broad application prospect. However, it is extremely difficult to achieve highly sensitive detection of polarized light for most organic semiconductor polymers with intrinsic isotropic amorphous behavior. In this study, the performance-enhanced intrinsic anisotropic all-polymer bulk heterojunctions (BHJs) are obtained by constructing molecular fluorination engineering in the fused-ring backbone of the acceptor polymer. The molecular orientation, alignment, and packing can be effectively optimized during the floating-film formation process without using any additives and post-treatments. The outstanding intrinsic polarization-sensitive photodetection performance with a very high photocurrent dichroic ratio of 3.73, a specific detectivity of 1.3 × 1011 Jones at 0 V, and a broad linear dynamic range of 120 dB is achieved for the optimum-fluorine-content self-assembly all-polymer organic BHJ film. The superiorities of self-powered capability, fast response, and high-contrast imaging demonstrate that the backbone fluorination for acceptor polymers is conducive to achieving excellent structural regularity and can endow the intrinsic polarization-sensitive all-polymer OPDs with more demanding polarized-light detection ability.

Novel porphyrin-based donor–acceptor conjugated organic polymers for efficient photocatalytic production of hydrogen peroxide in pure water

The N–H bond on the porphyrin ring serves as the O2 reduction site and undergoes a two-step one-electron oxygen reduction. Meanwhile, the benzene ring serves as the water oxidation site and undergoes 4e− water oxidation to produce O2.

Next-Generation Polymeric Organic Semiconductors for Electrochemical Transistors with Applications in Bioelectronics

Over the last decade, significant progress has been made in developing efficient mixed-organic-ionic-electronic conductors (OMIECs) for electrochemical transistors. Improvements in device performance for both transconductance and operational stability paved the way for applications of electrochemical transistors for health monitoring, neuromorphic computing, or electrochemical sensors. While the tuning of the energy levels (via backbone engineering) and the local environment of the polymers (via side-chain engineering) is reported to be a successful strategy for improving the electronic and ionic charge transport properties, little is known about how the short- and long-range order of polymers impacts the device performance.In my talk, I will discuss the importance of microstructure and dynamic microstructural rearrangements of OMIECs which greatly influence the electronic charge transport properties in electrochemical transistors [1]. By combining electrochemical and spectroelectrochemical measurements alongside electrochemical X-ray diffraction measurements, we observe that holes and anions are placed in ordered aggregates and crystallites at relatively low charge carrier densities (< 2x1020 cm-3) for selected OMIECs, explaining the large increase in transconductance at low operational voltages. Moreover, we find that the electrochemical charging of p-type polymeric OMIECs induces structural order along the polymer backbones. We interpret this structural ordering as the key factor for achieving high transconductance since percolating networks can form more easily when polymer chains are planarizing. Surprisingly, these dynamic microstructural rearrangements are highly reversible, however only when high charge carrier densities are avoided where bipolarons are forming. Based on these findings, I will discuss chemical design strategies for next-generation OMIECs with improved transconductance and operation stability in electrochemical transistors.[1] Garrett LeCroy, Camila Cendra, Tyler J. Quill, et.al., Role of aggregates and microstructure of mixed-ionicelectronic-conductors on charge transport in electrochemical transistors, Mater. Horiz., 2023, accepted.

Organic Semiconducting Polymers for Augmenting Biosynthesis and Bioconversion.

Solar-driven biosynthesis and bioconversion are essential for achieving sustainable resources and renewable energy. These processes harness solar energy to produce biomass, chemicals, and fuels. While they offer promising avenues, some challenges and limitations should be investigated and addressed for their improvement and widespread adoption. These include the low utilization of light energy, the inadequate selectivity of products, and the limited utilization of inorganic carbon/nitrogen sources. Organic semiconducting polymers offer a promising solution to these challenges by collaborating with natural microorganisms and developing artificial photosynthetic biohybrid systems. In this Perspective, we highlight the latest advancements in the use of appropriate organic semiconducting polymers to construct artificial photosynthetic biohybrid systems. We focus on how these systems can enhance the natural photosynthetic efficiency of photosynthetic organisms, create artificial photosynthesis capability of nonphotosynthetic organisms, and customize the value-added chemicals of photosynthetic synthesis. By examining the structure-activity relationships and emphasizing the mechanism of electron transfer based on organic semiconducting polymers in artificial photosynthetic biohybrid systems, we aim to shed light on the potential of this novel strategy for artificial photosynthetic biohybrid systems. Notably, these coupling strategies between organic semiconducting polymers and organisms during artificial photosynthetic biohybrid systems will pave the way for a more sustainable future with solar fuels and chemicals.

Organic semiconductor self-powered photoelectrochemical strategy for L. Monocytogenes detection coupled with target-triggered DNA polymerase activity

The materials involved in studies of self-powered modes are mainly focused on inorganic semiconductor, heterostructure and homojunction. Here, it was found that the self-powered characteristics can be realized based on the photocurrent of polymer organic semiconductor, amino-modified 3,4,9,10-perylenetetracarboxylic dianhydride polymer (PTC-NH2), which being mediated with methylene blue (Mb) and ascorbic acid (AA). A self-powered organic semiconductor photoelectrochemical (PEC) strategy based on co-mediation of Mb and AA was developed for L. monocytogenes detection. This PEC sensing strategy used the target to activate the activity of Taq DNA polymerase. The activated Taq DNA polymerase hydrolysis the DNA which being labeled with Mb. Thereby detaching Mb from magnetic beads (MBs), the strong photocurrent at 0 V with the combined action of AA was produced from PTC-NH2 modified ITO, and realize target detection sensitively. The limit of detection was 85 CFU/mL of L. monocytogenes. This research provides a promising application for the detection of target with the organic semiconductor self-powered PEC sensing strategy. It is anticipated this organic semiconductor self-powered method can give a promising approach for the design and development of low-power-consumption electronics and flexible wearable detection equipment.

Lest We Forget-The Importance of Heteroatom Interactions in Heterocyclic Conjugated Systems, from Synthetic Metals to Organic Semiconductors.

The field of synthetic metals is, and remains, highly influential for the development of organic semiconductor materials. Yet, with the passing of time and the rapid development of conjugated materials in recent years, the link between synthetic metals and organic semiconductors is at risk of being forgotten. This review reflectson one of the key concepts developed in synthetic metals - heteroatom interactions. The application of this strategy in recent organic semiconductor materials, small molecules and polymers, is highlighted, with analysis of X-ray crystal structures and comparisons with model systems used to determine the influence of these non-covalent short contacts. The case is made that the wide range of effective heteroatom interactions and the high performance that has been achieved in devices from organic solar cells to transistors is testament to the seeds sown by the synthetic metals research community.

Preparation of Novel Organic Polymer Semiconductor and Its Properties in Transistors through Collaborative Theoretical and Experimental Approaches.

Conjugated polymer semiconductors based on donor-acceptor structures are commonly employed as core materials for optoelectronic devices in the field of organic electronics. In this study, we designed and synthesized a novel acceptor unit thiophene-vinyl-diketopyrrolopyrrole, named TVDPP, based on a four-step organic synthesis procedure. Stille coupling reactions were applied with high yields of polymerization of TVDPP with fluorinated thiophene (FT) monomer. The molecular weight and thermal stability of the polymers were tested and showed high molecular weight and good thermal stability. Theoretical simulation calculations and 2D grazing-incidence wide-angle X-ray scattering (GIWAXS) tests verified the planarity of the material and excellent stacking properties, which are favorable for achieving high carrier mobility. Measurements based on the polymer as an organic thin film transistor (OTFT) device were carried out, and the mobility and on/off current ratio reached 0.383 cm2 V-1 s-1 and 104, respectively, showing its great potential in organic optoelectronics.

Rational Design of Novel Conjugated Terpolymers Based on Diketopyrrolopyrrole and Their Applications to Organic Thin-Film Transistors.

Organic polymer semiconductor materials, due to their good chemical modifiability, can be easily tuned by rational molecular structure design to modulate their material properties, which, in turn, affects the device performance. Here, we designed and synthesized a series of materials based on terpolymer structures and applied them to organic thin-film transistor (OTFT) device applications. The four polymers, obtained by polymerization of three monomers relying on the Stille coupling reaction, shared comparable molecular weights, with the main structural difference being the ratio of the thiazole component to the fluorinated thiophene (Tz/FS). The conjugated polymers exhibited similar energy levels and thermal stability; however, their photochemical and crystalline properties were distinctly different, leading to significantly varied mobility behavior. Materials with a Tz/FS ratio of 50:50 showed the highest electron mobility, up to 0.69 cm2 V-1 s-1. Our investigation reveals the fundamental relationship between the structure and properties of materials and provides a basis for the design of semiconductor materials with higher carrier mobility.

Donor-Acceptor-Based Organic Polymer Semiconductor Materials to Achieve High Hole Mobility in Organic Field-Effect Transistors.

Organic polymer semiconductor materials are conveniently tuned to energy levels because of their good chemically modifiable properties, thus enhancing their carrier transport capabilities. Here, we have designed and prepared a polymer with a donor-acceptor structure and tested its potential as a p-type material for organic field-effect transistor (OFET) applications using a solution-processing method. The conjugated polymers, obtained via the polymerization of the two monomers relying on the Stille coupling reaction, possess extremely high molecular weights and thermodynamic stability. Theoretical-based calculations show that PDPP-2S-Se has superior planarity, which is favorable for carrier transport within the main chain. Photophysical and electrochemical measurements systematically investigated the properties of the material and the energy levels with respect to the theoretical values. The maximum hole mobility of the PDPP-2S-Se-based OFET device is 0.59 cm2 V-1 s-1, which makes it a useful material for potential organic electronics applications.