Nonlinear optical (NLO) materials can be useful for a variety of applications varying from modulation of optical signals facilitated by the electro-optic effect-the effect whereby the refractive ...index of a material changes in response to an applied electric field-to microfabrication, sensing, imaging, and cancer therapy facilitated by multiphoton absorption, wherein molecules simultaneously absorb two or more photons of light. This short Focus article is a brief personal perspective of some of the key advances in second-order NLO materials and in multiphoton-absorbing materials, and of how and why these advances have led to renewed interest in organic NLO materials.
Perylene-3,4,9,10-tetracarboxylic acid diimides (perylene diimides, PDIs) have been used as industrial pigments for many years. More recently, new applications for PDI derivatives have emerged in ...areas including organic photovoltaic devices and field-effect transistors. This Perspective discusses the synthesis and physical properties of PDI derivatives and their applications in organic electronics.
We design and synthesize two isomeric fused-ring electron acceptors, FNIC1 and FNIC2, which have the same end-groups and side-chains, but isomeric fused-nine-ring cores. Subtle changes in the two ...isomers influence their electronic, optical, charge-transport, and morphological properties. As compared with FNIC1, FNIC2 film exhibits a red-shifted absorption peak at 794 nm (752 nm for FNIC1), larger electron affinity of 4.00 eV (3.92 eV for FNIC1), smaller ionization energy of 5.56 eV (5.61 eV for FNIC1), and higher electron mobility of 1.7 × 10–3 cm2 V–1 s–1 (1.2 × 10–3 cm2 V–1 s–1 for FNIC1). The as-cast organic solar cells based on PTB7-Th:FNIC2 blends exhibit a power conversion efficiency (PCE) of 13.0%, which is significantly higher than that of PTB7-Th:FNIC1-based devices (10.3%). Semitransparent devices based on PTB7-Th:FNIC2 blends exhibit PCEs varying from 9.51% to 11.6% at different average visible transmittance (AVT, 20.3– 13.6%), significantly higher than those of PTB7-Th:FNIC1-based devices (7.58–9.14% with AVT of 20.2– 14.7%).
Imine-linked two-dimensional covalent organic frameworks (2D COFs) are crystalline polymer networks with enhanced stability compared to boronate ester-linked systems and with broad monomer scope. ...They are traditionally prepared by condensing polyfunctional aldehydes and amines at elevated temperature in a mixture of organic solvents and aqueous CH3CO2H, which catalyzes imine formation and exchange. Here we employ metal triflates, which are water-tolerant Lewis acids, to accelerate 2D imine-linked COF synthesis and improve their materials quality. Low catalyst loadings provide crystalline polymer networks in nearly quantitative yields. These conditions are demonstrated for several COFs, including heteroatom-containing systems of interest for optoelectronic applications.
The performance of lead‐halide perovskite light‐emitting diodes (LEDs) has increased rapidly in recent years. However, most reports feature devices operated at relatively small current densities ...(<500 mA cm−2) with moderate radiance (<400 W sr−1 m−2). Here, Joule heating and inefficient thermal dissipation are shown to be major obstacles toward high radiance and long lifetime. Several thermal management strategies are proposed in this work, such as doping charge‐transport layers, optimizing device geometry, and attaching heat spreaders and sinks. Combining these strategies, high‐performance perovskite LEDs are demonstrated with maximum radiance of 2555 W sr−1 m−2, peak external quantum efficiency (EQE) of 17%, considerably reduced EQE roll‐off (EQE > 10% to current densities as high as 2000 mA cm−2), and tenfold increase in operational lifetime (when driven at 100 mA cm−2). Furthermore, with proper thermal management, a maximum current density of 2.5 kA cm−2 and an EQE of ≈1% at 1 kA cm−2 are shown using electrical pulses, which represents an important milestone toward electrically driven perovskite lasers.
Several thermal management strategies are proposed and applied to perovskite light‐emitting diodes (LEDs), resulting in greatly reduced efficiency roll‐off, record high radiance, and significantly improved operational lifetime. Furthermore, these thermal management strategies enable pulsed operation of perovskite LEDs in the kA cm‐2 range with much improved device performance, an important step toward electrically driven perovskite lasers.
Organic semiconductors have been the subject of intensive academic and commercial interest over the past two decades, and successful commercial devices incorporating them are slowly beginning to ...enter the market. Much of the focus has been on the development of hole transporting, or p‐type, semiconductors that have seen a dramatic rise in performance over the last decade. Much less attention has been devoted to electron transporting, or so called n‐type, materials, and in this paper we focus upon recent developments in several classes of n‐type materials and the design guidelines used to develop them.
Recent progress in the development of n‐type organic semiconductors for a range of applications, including field‐effect transistors and solar cells is reviewed. We focus on the design guidelines used to develop n‐type materials by examining several illustrative materials classes including fullerenes, rylenes, acenes, and siloles.
Transparent conducting oxides (TCOs), such as indium tin oxide and zinc oxide, play an important role as electrode materials in organic-semiconductor devices. The properties of the inorganic–organic ...interfacethe offset between the TCO Fermi level and the relevant transport level, the extent to which the organic semiconductor can wet the oxide surface, and the influence of the surface on semiconductor morphologysignificantly affect device performance. This review surveys the literature on TCO modification with phosphonic acids (PAs), which has increasingly been used to engineer these interfacial properties. The first part outlines the relevance of TCO surface modification to organic electronics, surveys methods for the synthesis of PAs, discusses the modes by which they can bind to TCO surfaces, and compares PAs to alternative organic surface modifiers. The next section discusses methods of PA monolayer deposition, the kinetics of monolayer formation, and structural evidence regarding molecular orientation on TCOs. The next sections discuss TCO work-function modification using PAs, tuning of TCO surface energy using PAs, and initiation of polymerizations from TCO-tethered PAs. Finally, studies that examine the use of PA-modified TCOs in organic light-emitting diodes and organic photovoltaics are compared.
Here we report that a covalent organic framework (COF), which contains 2,5-di(imine)-substituted 1,4-dihydroxybenzene (diiminol) moieties, undergoes color changes in the presence of solvents or ...solvent vapor that are rapid, passive, reversible, and easily detectable by the naked eye. A new visible absorption band appears in the presence of polar solvents, especially water, suggesting reversible conversion to another species. This reversibility is attributed to the ability of the diiminol to rapidly tautomerize to an iminol/cis-ketoenamine and its inability to doubly tautomerize to a diketoenamine. Density functional theory (DFT) calculations suggest similar energies for the two tautomers in the presence of water, but the diiminol is much more stable in its absence. Time-dependent DFT calculations confirm that the iminol/cis-ketoenamine absorbs at longer wavelength than the diiminol and indicate that this absorption has significant charge-transfer character. A colorimetric humidity sensing device constructed from an oriented thin film of the COF responded quickly to water vapor and was stable for months. These results suggest that tautomerization-induced electronic structure changes can be exploited in COF platforms to give rapid, reversible sensing in systems that exhibit long-term stability.
Persistent emission with a long lifetime (>1 s) from organic materials can only be observed at a low temperature, because of the significant nonradiative deactivation pathway that occurs at ...room‐temperature (RT). If organic materials with persistent RT emission in air could be developed, they could potentially be utilized for a variety of applications. Here, organic host‐guest materials with efficient persistent RT phosphorescence (RTP) are developed by minimizing the nonradiative deactivation pathway of triplet excitons. The nonradiative deactivation pathway is dependent on both nonradiative deactivation of the guest and quenching by diffusional motion of the host. The rigidity and oxygen barrier properties of the steroidal compound used as the host suppressed the quenching, and the aromatic hydrocarbon used as the guest is highly deuterated to minimize nonradiative deactivation of the guest. Red‐green‐blue persistent RTP with a lifetime >1 s and a quantum yield >10% in air is realized for a pure organic material.
Efficient persistent room temperature phosphorescence with a quantum efficiency of greater than 10% and a lifetime longer than 1 s from pure organic amorphous host‐guest materials is demonstrated in air. Physical rigidity and oxygen blocking characteristics of amorphous steroidal compounds as the host greatly minimize quenching of long‐lifetime triplet exitons of the guest by interaction with the host and oxygen.
Organic electron‐transporting materials are essential for the fabrication of organic p‐n junctions, photovoltaic cells, n‐channel field‐effect transistors, and complementary logic circuits. Rylene ...diimides are a robust, versatile class of polycyclic aromatic electron‐transport materials with excellent thermal and oxidative stability, high electron affinities, and, in many cases, high electron mobilities; they are, therefore, promising candidates for a variety of organic electronics applications. In this review, recent developments in the area of high‐electron‐mobility diimides based on rylenes and related aromatic cores, particularly perylene‐ and naphthalene‐diimide‐based small molecules and polymers, for application in high‐performance organic field‐effect transistors and photovoltaic cells are summarized and analyzed.
Electronic devices based on organic materials offer the potential of low‐cost processing on flexible substrates when compared to traditional inorganic semiconductors. Rylene diimides have recently shown promise as potential alternatives to the fullerenes as acceptors in photovoltaic devices, exhibiting power conversion efficiencies that are amongst the highest achieved for all‐polymer fullerene‐free systems. This article reviews their development for both transistor and solar cell applications.
