Development Of Organic Semiconductors Research Articles

Degradable n‐Type Organic Semiconductors Based on Knoevenagel Condensation Reaction

AbstractThe increasing amount of electronic exerts a profound impact on both the environment and human health. Looking forward, it is imperative to develop electronic products that can degrade under mind condition, which largely relies on the development of degradable organic semiconductors (OSCs). Yet, designing degradable OSCs with decent electrical properties is challenging. In this study, two degradable n‐type OSCs based on a dynamic covalent C═C bond formed via the Knoevenagel condensation reaction are reported. The cleavage of Knoevenagel formed C═C bond through a retro‐Knoevenagel process imparts the degradability of these two OSCs in the weak base, particularly in the human‐friendly α‐amino acid of lysine. Meanwhile, the C═C bond formed by Knoevenagel reaction preserves optimal backbone planarity and good electron delocalization of the molecules. This, in turn, endows the OSCs with commendable electron transport performance, achieving an electron mobility of up to 0.57 cm2 V⁻¹ s⁻¹ in organic thin‐film transistors. This work provides a new insight into the molecular design strategy for the development of OSCs with degradability and good electrical properties.

Helical Polycyclic Heteroaromatic as Hole Transport Material for Perovskite Solar Cell: Remarkable Impact of Alkyl Substitution Position

AbstractPolycyclic aromatic hydrocarbons play a critical role in the development of organic semiconductors. This study unravels the impact of alkyl substitution position on the molecular energy level, glass transition temperature, diffusion of external species, and hole transport of a pyrrole‐rich, helical polycyclic heteroaromatic, that is TBPC. Compared to terminal substitution, internal hexyl substitution results in steric repulsion with TBPC, weakening π─π stacking and therefore improving thin film morphology. Internal substitution also reduces energy disorder, lowers reorganization energy, and increases intermolecular transfer integrals, leading to enhanced hole mobility. Notably, the organic semiconductor with internal hexyl substitution (TBPC‐611) exhibits a higher molecular packing density, resulting in a markedly higher glass transition temperature and slower diffusion of external species. Using TBPC‐611 as the hole transport material, this work successfully fabricates perovskite solar cells with an average power conversion efficiency above 24%, showing good photostability and thermostability. These findings contribute new insights to the development of high‐performance organic semiconductors.

Stretchable and Self-Healing Elastomers with Aggregation-Induced Emission Based on Hydrogen Bonding Cross-Linked Networks

With the fast advancement of flexible and stretchable electronics, the development of organic semiconductors with intrinsic stretchability and self-healing properties is desirable and significant yet remains a substantial challenge. Herein, we propose a simple and effective synthetic strategy to construct intrinsically stretchable and self-healing organic light-emitting elastomers via incorporating aggregation-induced emission (AIE) luminogens into hydrogen-bonding cross-linked networks. Owing to the hydrogen-bonding interactions within the networks, the resulting light-emitting elastomers achieved a stress–strain of about 700% and a self-healing efficiency of over 70% under ambient conditions. More importantly, the resulting elastomers have been examined to be highly adhesive and compatible with the silver nanowire networks, exhibiting smart luminescence behaviors and excellent conductivity. This study sheds light on the design and development of stretchable and self-healing organic light-emitting elastomers with promising optoelectronic characteristics, which would inspire a wide range of fancy applications for flexible and stretchable electronics.

The Role of Electrochemical and Spectroelectrochemical Techniques in the Preparation and Characterization of Conjugated Polymers: From Polyaniline to Modern Organic Semiconductors.

This review article presents different electrochemical and spectroelectrochemical techniques used to investigate conjugated polymers. The development of this research area is presented from an over 40-year perspective—the period of research carried out by Professor Mieczyslaw Lapkowski. Initial research involved polymers derived from simple aromatic compounds, such as polyaniline. Since then, scientific advances in the field of conductive polymers have led to the development of so-called organic electronics. Electrochemical and spectroelectrochemical methods have a great influence in the development of organic semiconductors. Their potential for explaining many phenomena is discussed and the most relevant examples are provided.

Toward More Efficient Organic Semiconductors: The Relationship between Morphology, Charge Transport, and Photophysical Properties

In recent years, materials science has been facing an electronics revolution due to the fast progress in the development of organic semiconductors. In this context, the current study attempts to tune the photophysical properties of polycyclic aromatic hydrocarbons (PAHs) by engineering their morphology and size. Four families of PAHs─oligoacenes, circulenes, triangulenes, and sunflowers─are considered to investigate the evolution of their optoelectronic properties with size and morphology. Based on the calculated properties, several quantitative structure–property relationships have been established for the prediction of reorganization energy. It is found that morphologies like circulene and triangulene that are less aromatic and have smaller energy gaps achieve smaller reorganization energy and thus are better candidates for charge transport materials. For all considered PAHs, the excitation energies of the strongest low-lying electronic transition (β peak) span in the visible region and demonstrate the size tunability. The β peak of some oligoacene and triangulene families exhibits plasmonic behavior that is important for the fabrication of lighter optical devices compared with metallic systems. We have also explored the effect of sulfur heteroatoms on the structural, electronic, and optical properties of circulene and sunflower morphologies.

Alkyl-Substituted Selenium-Bridged V-Shaped Organic Semiconductors Exhibiting High Hole Mobility and Unusual Aggregation Behavior.

Toward the development of high-performance organic semiconductors (OSCs), carrier mobility is the most important requirement for next-generation OSC-based electronics. The strategy is that OSCs consisting of a highly extended π-electron core exhibit two-dimensional (2D) aggregated structures to offer effective charge transport. However, such OSCs, in general, show poor solubility in common organic solvents, resulting in limited solution processability. This is a critical trade-off between the development of OSCs with simultaneous high carrier mobility and suitable solubility. To address this issue, herein, five-membered ring-fused selenium-bridged V-shaped binaphthalene with decyl substituents (C10-DNS-VW) is developed and synthesized by an efficient method. C10-DNS-VW exhibits significantly high solubility for solution processes. Notably, C10-DNS-VW forms a one-dimensional π-stacked packing motif (1D motif) and a 2D herringbone (HB) packing motif (2D motif), depending on the crystal growth condition. On the other hand, the fabrication of thin films by means of both solution process and vacuum deposition techniques forms only the 2D HB motif. External stress tests such as heating and exposure to solvent vapor indicated that 1D and 2D motifs could be synergistically induced by the total balance of intermolecular interactions. Finally, the single-crystalline films of C10-DNS-VW by solution process exhibit carrier mobility up to 11 cm2 V-1 s-1 with suitable transistor stability under ambient conditions for more than two months, indicating that C10-DNS-VW is one of the most promising candidates for breaking the trade-off in the field of solution-processed technologies.

Fabrication of Hybrid Membranes Containing Nylon-11 and Organic Semiconductor Particles with Potential Applications in Molecular Electronics.

Chemical degradation is a major disadvantage in the development of organic semiconductors. This work proposes the manufacture and characterization of organic semiconductor membranes in order to prevent semiconductor properties decreasing. Semiconductor membranes consisting of Nylon-11 and particles of π-conjugated molecular semiconductors were manufactured by high-vacuum evaporation followed by thermal relaxation. Initially, and with the aim of obtaining semiconductor particles, bulk heterojunction (BHJ) was carried out using green chemistry techniques between the zinc phthalocyanine (ZnPc) and the zinc hexadecafluoro-phthalocyanine (F16ZnPc) as n-type molecular semiconductors with the p-type molecular semiconductor dibenzotetrathiafulvalene (DBTTF). Consequently, the π-conjugated semiconductors particles were embedded in a Nylon-11 matrix and characterized, both structurally and considering their optical and electrical properties. Thin films of these materials were manufactured in order to comparatively study the membranes and precursor semiconductor particles. The membranes presented bandgap (Eg) values that were lower than those obtained in the films, which is an indicator of an improvement in their semiconductor capacity. Finally, the membranes were subjected to accelerated lighting conditions, to determine the stability of the polymer and the operating capacity of the membrane. After fatigue conditions, the electrical behavior of the proposed semiconductor membranes remained practically unaltered; therefore, they could have potential applications in molecular electronics. The chemical stability of membranes, which did not degrade in their polymer compound, nor in the semiconductor, was monitored by IR spectroscopy.

Next-generation organic semiconductors driven by bent-shaped π-electron cores

The development of organic semiconductors (OSCs) applicable to organic field-effect transistors (OFETs) is crucial to realizing printed and flexible electronics, such as flexible displays and low-priced identification tags. OSCs for printed and flexible electronics must meet several prerequisites: (1) high chemical stability for use without special care, (2) charge carrier mobility exceeding 10 cm2/Vs for several applications, (3) appropriate solubility in organic solvents for solution processes, (4) high thermal durability for device fabrications and applications, and (5) a simple synthetic route for large-scale production. Previously reported OSCs do not meet all the requirements simultaneously, which has motivated intensive development of OSCs for future printed and flexible electronics applications. The author and collaborators developed state-of-the-art OSCs based on bent-shaped π-electron cores (π-cores) that satisfy the requirements for printed semiconductor devices. In this focused review, the chemistry and device engineering are introduced with respect to sulfur-bridged V-shaped and N-shaped π-cores among a series of bent-shaped π-cores. The development of organic semiconductors (OSCs) applicable to organic field-effect transistors is crucial to printed and flexible electronics. OSCs must meet several prerequisites: 1) high chemical stability, 2) charge carrier mobility exceeding 10 cm2/Vs, 3) appropriate solubility, and 4) high thermal durability. The author and collaborators developed state-of-the-art OSCs based on bent-shaped π-electron cores (π-cores) that satisfy the requirements for printed semiconductor devices. In this focused review, the chemistry and device engineering are introduced with respect to sulfur-bridged V-shaped and N-shaped π-cores among a series of bent-shaped π-cores.

(Invited) Organic and Inorganic Materials for Efficient Pb and Pb-Free Perovskite Solar Cells

Perovskite solar cells have attracted much attention as cost-effective next generation printable photovoltaics. In a relatively short period, power conversion efficiencies in such cells have been substantially increased, mainly due to improvements of the fabrication protocols for the perovskite layer as well as the development of new materials for buffer layers. Our approaches toward efficient lead and lead-free perovskite solar cells are as follows. 1) Development of organic semiconductors as efficient charge-collection layer: We design and synthesis of novel p-conjugated materials in terms of control of the energy level of frontier orbitals and molecular aggregation. 2) Development of highly purified perovskite precursor materials: We synthesis of a series of complexes of lead halides or tin halides as purified precursor for perovskite materials. 3) Development of fabrication methods for perovskite layer by solution process: We focus on the intermediates formed during the solution process and develop efficient fabrication methods based on the mechanism. In this talk, we introduce our recent progress on tin halide perovskite solar cells as well as lead halide perovskites.

Ladder-type heteroheptacene-cored semiconductors for small-molecule solar cells

The development of organic semiconductors is essential to improve the performance of organic solar cells (OSCs). In this work, a carbazole-based heteroheptacene (HHA) building block is first used to construct two semiconducting small molecules (CDTRH and C3TRH) with different conjugation lengths. The conjugation length of the small molecules (SMs) has a significant impact on the device performance of bulk heterojunction (BHJ) OSCs based on them and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM). CDTRH/PC71BM blend film exhibits a clear phase separation with smaller domain sizes compared to those based on C3TRH/PC71BM due to the shorter conjugation length of the former SM. Meanwhile, compared to C3TRH, CDTRH shows a higher hole mobility of 3.25 × 10−5 cm2 V−1 s−1 which contributes to the better performance of corresponding solar cells. Finally, OSCs based on CDTRH exhibit a power conversion efficiency (PCE) of 6.19% with an open-circuit voltage of 1.01 V, a short-circuit current of 14.36 mA cm−2, which is the best result in any ladder-type heteroheptacene-based SMs for OSCs. The PCE of 6.19% is much higher than the 3.83% PCE for the C3TRH-based devices fabricated under the same condition. These findings indicate that in combination with a suitable conjugation bridge, the ladder-type HHA core is a promising for developing efficient p-type SM semiconductors for OSCs.

Recent progress in the development of n-type organic semiconductors for organic field effect transistors

This article reviews recent major progress in the development of organic semiconductors as electron transport n-channel materials in organic field effect transistors (OFETs).

Furan-containing conjugated polymers for organic solar cells

Development of organic semiconductors is one of the most intriguing and productive topics in material science and engineering. Many efforts have been made on the synthesis of aromatic building blocks such as benzene, thiophene and pyrrole due to the facile preparation accompanied by the intrinsic environmental stability and relatively efficient properties of the resulting polymers. In the past, furan has been less explored in this field because of its high oxidation potential. Recently, furan has attracted obsession due to its weaker aromaticity, the greater solubilities of furan-containing π-conjugated polymers relative to other benzenoid systems and the accessibility of furan-based starting materials from renewable resources. This review elaborates the advancements of organic photovoltaic polymers containing furan building blocks. The uniqueness and advantages of furan-containing building blocks in semiconducting materials are also discussed.

Theoretical Approach for the Development of Organic Semiconductors on the Basis of the MO Symmetry: Thienoacene as an Example

ABSTRACTWe have explored materials for organic field-effect transistors (OFETs) from the viewpoint of theoretical calculations. The herringbone structure, which realizes two-dimensional conduction, is investigated in detail. Transfer integrals (t) are calculated systematically as a function of the dihedral angle between the molecular planes (θ) and the displacement along the molecular long axis (D). Acenes, oligothiophenes, thienoacenes and tetrathiafulvalenes are investigated, and are discussed from the molecular orbital (MO) symmetry. Thienoacenes (nTAs) are particularly examined as a candidate of OFET materials from the calculations of transfer integrals and reorganization energies (λ) based on the energy levels and the MO symmetry. LUMO of nTAs have MO symmetry suitable for conduction, but these orbitals are usually not related to the conduction. We have investigated the electronic properties of the derivatives with dicarboximide moiety. nTA-tetracarboxydiimide is expected to show the herringbone structure and exhibit n-type transport from the properties of LUMO.

Controlled Deposition of Crystalline Organic Semiconductors for Field‐Effect‐Transistor Applications

AbstractThe search for low‐cost, large‐area, flexible devices has led to a remarkable increase in the research and development of organic semiconductors, which serve as one of the most important components for organic field‐effect transistors (OFETs). In the current review, we highlight deposition techniques that offer precise control over the location or in‐plane orientation of organic semiconductors. We focus on various vapor‐ and solution‐processing techniques for patterning organic single crystals in desired locations. Furthermore, the alignment of organic semiconductors via different methods relying on mechanical forces, alignment layers, epitaxial growth, and external magnetic and electric fields are surveyed. The advantages, limitations, and applications of these techniques in OFETs are also discussed.

From One‐ to Three‐Dimensional Organic Semiconductors: In Search of the Organic Silicon?

AbstractOrganic semiconductors based on π‐conjugated systems are the focus of considerable interest in the emerging area of soft or flexible photonics and electronics. Whereas in recent years the performances of devices such as organic light‐emitting diodes (OLEDs), organic field‐effect transistors (OFETs), or solar cells have undergone considerable progress, a number of technical and fundamental problems related to the low dimensionality of organic semiconductors based on linear π‐conjugated systems remain unsatisfactorily resolved. This low dimensionality results in an anisotropy of the optical and charge‐transport properties, which in turn implies a control of the material organization/molecular orientation during or after device fabrication. Such a constraint evidently represents a problem when device fabrication by solution‐based processes, such as printing techniques, is envisioned. The aim of this short Review is to illustrate possible alternative strategies based on the development of organic semiconductors with higher dimensionality, capable to exhibit isotropic electronic properties.