Organic (opto)electronic materials have received considerable attention due to their applications in thin-film-transistors, light-emitting diodes, solar cells, sensors, photorefractive devices, and many others. The technological promises include low cost of these materials and the possibility of their room-temperature deposition from solution on large-area and/or flexible substrates. The article reviews the current understanding of the physical mechanisms that determine the (opto)electronic properties of high-performance organic materials. The focus of the review is on photoinduced processes and on electronic properties important for optoelectronic applications relying on charge carrier photogeneration. Additionally, it highlights the capabilities of various experimental techniques for characterization of these materials, summarizes top-of-the-line device performance, and outlines recent trends in the further development of the field. The properties of materials based both on small molecules and on conjug...

Organic Optoelectronic Materials: Mechanisms and Applications

In this paper, two near-infrared absorbing molecules are successfully incorporated into nonfullerene-based small-molecule organic solar cells (NFSM-OSCs) to achieve a very high power conversion efficiency (PCE) of 12.08%. This is achieved by tuning the sequentially evolved crystalline morphology through combined solvent additive and solvent vapor annealing, which mainly work on ZnP-TBO and 6TIC, respectively. It not only helps improve the crystallinity of the ZnP-TBO and 6TIC blend, but also forms multilength scale morphology to enhance charge mobility and charge extraction. Moreover, it simultaneously reduces the nongeminate recombination by effective charge delocalization. The resultant device performance shows remarkably enhanced fill factor and Jsc . These result in a very respectable PCE, which is the highest among all NFSM-OSCs and all small-molecule binary solar cells reported so far.

Over 12% Efficiency Nonfullerene All-Small-Molecule Organic Solar Cells with Sequentially Evolved Multilength Scale Morphologies

We report the first highly efficient artificial light-harvesting systems based on nanocrystals of difluoroboron chromophores to mimic the chlorosomes, one of the most efficient light-harvesting systems found in green photosynthetic bacteria. Uniform nanocrystals with controlled donor/acceptor ratios were prepared by simple coassembly of the donors and acceptors in water. The light-harvesting system funneled the excitation energy collected by a thousand donor chromophores to a single acceptor. The well-defined spatial organization of individual chromophores in the nanocrystals enabled an energy transfer efficiency of 95 %, even at a donor/acceptor ratio as high as 1000:1, and a significant fluorescence of the acceptor was observed up to donor/acceptor ratios of 200 000:1.

Light‐Harvesting Systems Based on Organic Nanocrystals To Mimic Chlorosomes

Metal@semiconductor core-shell nanocrystals with atomically organized interfaces for efficient hot electron-mediated photocatalysis

Many studies have been conducted regarding the separation behavior of carriers (electrons and holes) because of involving the generation of superoxide radicals (O2− ), hydroxyl radicals (HO ), and hydrogen peroxide (H2O2) in the photocatalytic process of heteropolyacids. Instead, relatively little attention has been focused on the potential Coulomb interactions between photogenerated electrons (e−) and holes (h+). Herein, choline-phosphotungstic acid (Ch3-HPW) was synthesized via one-step acid-base neutralization reaction method, and characterized. The electronic excited state analysis of Ch3-HPW showed that the formation of singlet oxygen (1O2) was related to the electron-hole interactions in the photocatalytic process of ground state molecular oxygen (3O2) activation. Subsequently, a facile fuel photocatalytic oxidative desulfurization and extraction system was established on the basis of Ch3-HPW, air, and acetonitrile (MeCN), to better understand the 3O2 activation in specific applications. The main photocatalytic reaction conditions affecting the desulfurization process, including the amount of Ch3-HPW, the volume ratio of MeCN to model oil, the initial S-concentration, air/N2 bubbling, sulfur compounds, and fuel composition, were systematically investigated under UV radiation. The sulfur removal for model oil and straight-run gasoline in the system were 99.6% and 89.9%, respectively. The results of radical scavenger experiments, electron spin-resonance (ESR) spectroscopy, and density functional theory (DFT) calculations further demonstrated that 1O2, H2O2, and h+ played important roles in the oxidation of sulfur-containing compounds. A new method was developed for the desulfurization of liquid fuels using green and inexpensive O2 in this work to promote the development of photocatalytic process of exciton-involved HPA-based photocatalysts.

Electron-hole interactions in choline-phosphotungstic acid boosting molecular oxygen activation for fuel desulfurization

Confirmation of direct photogeneration of intrinsic delocalized free carriers in small-molecule organic semiconductors has been a long-sought but unsolved issue, which is of fundamental significance to its application in photo-electric devices. Although the excitonic description of photoexcitation in these materials has been widely accepted, this concept is challenged by recently reported phenomena. Here we report observation of direct delocalized free carrier generation upon interband photoexcitation in highly crystalline zinc phthalocyanine films prepared by the weak epitaxy growth method using ultrafast spectroscopy. Transient absorption spectra spanning the visible to mid-infrared region revealed the existence of short-lived free electrons and holes with a diffusion length estimated to cross at least 11 molecules along the π-π stacking direction that subsequently localize to form charge transfer excitons. The interband transition was evidenced by ultraviolet-visible absorption, photoluminescence and electroluminescence spectroscopy. Our results suggest that delocalized free carriers photogeneration can also be achieved in organic semiconductors when the molecules are packed properly.

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Photogenerated Intrinsic Free Carriers in Small-molecule Organic Semiconductors Visualized by Ultrafast Spectroscopy.

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Photogenerated Intrinsic Free Carriers in Small-molecule Organic Semiconductors Visualized by Ultrafast Spectroscopy.