以昇陳

Solution‐processed ternary oxides exhibit tunable optical and electrical properties in carrier transport layers for optoelectronic applications. Many ternary oxides have been developed with desirable properties to cater to various photoactive materials. In this review, the impacts of composition tuning in ternary oxide on achieving high‐performance and stable organic and perovskite optoelectronic devices are summarized.

Abstract

With the remarkable progress in solution‐processed optoelectronics, high performance is required of the carrier transport/injection layer. Ternary oxides containing a variety of crystal structures, and adjustable composition that results in tunable optical and electrical properties, are one of the promising class of candidates to fulfill the requirements of carrier transport/injection layers for high‐performance and stable optoelectronic devices. Solution‐processed ternary oxides have seen considerable progress in recent decades, due to their advantages in the quest to design low‐cost, high‐performance, large‐scale, and stable optoelectronic devices. Herein, the recent advances of solution‐processed ternary oxides are reviewed. The first section consists of a brief introduction to the topic. In the following section, the fundamentals of the effect of tuning ternary oxide composition are summarized. Section three briefly reviews the synthesis approaches for preparing ternary oxides. Section four discusses the recent progress of solution‐processed ternary oxide as carrier transport/injection layer in optoelectronic devices (such as organic solar cells, perovskite solar cells, organic light emitting diodes, etc.). In this section, the impact of controlling ternary oxide composition on device performance and stability is highlighted. Finally, a brief summary and an outlook are given.

Machine‐learning approaches are utilized to build models for the prediction of efficiency using important frontier molecular orbital energy levels of organic materials as features. Furthermore, a versatile Random Forest model reveals that the lowest unoccupied molecular orbital energy of donor can be considered as a critical feature in design of ternary organic solar cells.

Abstract

Ternary organic solar cells (OSCs) have progressed significantly in recent years due to the sufficient photon harvesting of the blend photoactive layer including three absorption‐complementary materials. With the rapid development of highly efficient ternary OSCs in photovoltaics, the precise energy‐level alignment of the three active components within ternary OSC devices should be taken into account. The machine‐learning technique is a computational method that can effectively learn from previous historical data to build predictive models. In this study, a dataset of 124 fullerene derivatives‐based ternary OSCs is manually constructed from a diverse range of literature along with their frontier molecular orbital theory levels, and device structures. Different machine‐learning algorithms are trained based on these electronic parameters to predict photovoltaic efficiency. Thus, the best predictive capability is provided by using the Random Forest approach beyond other machine‐learning algorithms in the dataset. Furthermore, the Random Forest algorithm yields valuable insights into the crucial role of lowest unoccupied molecular orbital energy levels of organic donors in the performance of ternary OSCs. The outcome of this study demonstrates a smart strategy for extracting underlying complex correlations in fullerene derivatives‐based ternary OSCs, thereby accelerating the development of ternary OSCs and related research fields.

Solution‐processed red fluorescent organic light‐emitting diodes (OLEDs) with external quantum efficiencies of up to 22.5% are fabricated using a synergistic strategy of molecular engineering and host selection with thermally activated delayed‐fluorescence emitters. With this strategy, a good balance of the critical photophysical parameters is realized by effectively fine tuning the excited states of the emitters, which is verified to support the record‐high efficiency reported.

Abstract

Developing high‐efficiency solution‐processable thermally activated delayed‐fluorescence (TADF) emitters, especially in longer wavelength regions, is a formidable challenge. Three red TADF emitters, namely NAI_R1, NAI_R2, and NAI_R3, are developed by phenyl encapsulation and tert‐butyl substitution on a prototypical 1,8‐naphthalimide‐acridine hybrid. This design strategy not only grants these molecules high solubility, excellent thermal stability, and good film‐forming ability, but also pulls down their charge‐transfer (CT) energy levels excited states. Furthermore, dispersing these emitters into two different host materials of mCP and mCPCN finely tailors their CT‐state energy levels. More importantly, a synergistic combination of molecular engineering and host selection can effectively manipulate the competition between the radiative and nonradiative decay rates of the CT singlet states of these emitters and the reverse intersystem crossing from their triplet to singlet states. Consequently, the optimal combination of NAI_R3 emitter and mCP host successfully results in a state‐of‐the‐art external quantum efficiency (EQE) of 22.5% for solution‐processed red TADF organic light‐emitting diodes (OLEDs) with an emission peak above 620 nm. This finding demonstrates that a synergistic strategy of molecular engineering and host selection with TADF emitters could provide a new pathway for developing efficient solution‐processable TADF systems.

Next‐generation solar cells consisting of organic materials are studied. To develop novel dyes for dye‐sensitized solar cells, the essential dye structures are explored to attain high efficiency. Additionally, the interfaces in the perovskite solar cells are characterized via electrochemical methods, and newly developed laser deposition methods for perovskite layers are discussed.

Abstract

Next‐generation organic solar cells such as dye‐sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are studied at the National Institute of Advanced Industrial Science and Technology (AIST), and their materials, electronic properties, and fabrication processes are investigated. To enhance the performance of DSSCs, the basic structure of an electron donor, π‐electron linker, and electron acceptor, i.e., D–π–A, is suggested. In addition, special organic dyes containing coumarin, carbazole, and triphenylamine electron donor groups are synthesized to find an effective dye structure that avoids charge recombination at electrode surfaces. Meanwhile, PSCs are manufactured using both a coating method and a laser deposition technique. The results of interfacial studies demonstrate that the level of the conduction band edge (CBE) of a compact TiO₂ layer is shifted after TiCl₄ treatment, which strongly affects the solar cell performance. Furthermore, a special laser deposition system is developed for the fabrication of the perovskite layers of PSCs, which facilitates the control over the deposition rate of methyl ammonium iodide used as their precursor.

Nature Photonics, Published online: 17 June 2019; doi:10.1038/s41566-019-0463-x

A simple yet effective side chain modulation on the backbone for obtaining both enhanced V _oc and J _sc simultaneously is demonstrated in this work. Compared with the controlled molecule 3TT‐CIC, 3TT‐OCIC showed PCE of 13.13% with improved V _oc of 0.69 V and J _sc of 27.58 mA cm⁻², and the tandem device gives an excellent efficiency of 15.72%.

Abstract

It is a great challenge to simultaneously improve the two tangled parameters, open circuit voltage (V _oc) and short circuit current density (J _sc) for organic solar cells (OSCs). Herein, such a challenge is addressed by a synergistic approach using fine‐tuning molecular backbone and morphology control simultaneously by a simple yet effective side chain modulation on the backbone of an acceptor–donor–acceptor (A–D–A)‐type acceptor. With this, two terthieno[3,2‐b]thiophene (3TT) based A–D–A‐type acceptors, 3TT‐OCIC with backbone modulation and 3TT‐CIC without such modification, are designed and synthesized. Compared with the controlled molecule 3TT‐CIC, 3TT‐OCIC shows power conversion efficiency (PCE) of 13.13% with improved V _oc of 0.69 V and J _sc of 27.58 mA cm⁻², corresponding to PCE of 12.15% with V _oc of 0.65 V and J _sc of 27.04 mA cm⁻² for 3TT‐CIC–based device. Furthermore, with effective near infrared absorption, 3TT‐OCIC is used as the rear subcell acceptor in a tandem device and gave an excellent PCE of 15.72%.

An energetic cascade between mixed and pure regions assists in suppressing recombination losses in nonfullerene acceptor (NFA)‐based organic solar cells. The impact of polymer–NFA blend composition upon film morphology, energetics, charge carrier recombination kinetics, and photocurrent properties is studied.

Abstract

Here, it is investigated whether an energetic cascade between mixed and pure regions assists in suppressing recombination losses in non‐fullerene acceptor (NFA)‐based organic solar cells. The impact of polymer‐NFA blend composition upon morphology, energetics, charge carrier recombination kinetics, and photocurrent properties are studied. By changing film composition, morphological structures are varied from consisting of highly intermixed polymer‐NFA phases to consisting of both intermixed and pure phase. Cyclic voltammetry is employed to investigate the impact of blend morphology upon NFA lowest unoccupied molecular orbital (LUMO) level energetics. Transient absorption spectroscopy reveals the importance of an energetic cascade between mixed and pure phases in the electron–hole dynamics in order to well separate spatially localized electron–hole pairs. Raman spectroscopy is used to investigate the origin of energetic shift of NFA LUMO levels. It appears that the increase in NFA electron affinity in pure phases relative to mixed phases is correlated with a transition from a relatively planar backbone structure of NFA in pure, aggregated phases, to a more twisted structure in molecularly mixed phases. The studies focus on addressing whether aggregation‐dependent acceptor LUMO level energetics are a general design requirement for both fullerene and NFAs, and quantifying the magnitude, origin, and impact of such energetic shifts upon device performance.

Among all existing near‐infrared (NIR)‐II fluorophores, the NIR‐II molecular dyes are the most remarkable in translating this imaging window into the clinical setting. Advanced NIR‐II dye‐derived bioconjugates will give doctors an unparalleled view into tissues for tumor detection at greater depths and contrast, allowing early detection during cancer screenings and solid tumor resection by delineation of the boundaries between healthy and cancerous tissues.

Abstract

Fluorescence bioimaging affords a vital tool for both researchers and surgeons to molecularly target a variety of biological tissues and processes. This review focuses on summarizing organic dyes emitting at a biological transparency window termed the near‐infrared‐II (NIR‐II) window, where minimal light interaction with the surrounding tissues allows photons to travel nearly unperturbed throughout the body. NIR‐II fluorescence imaging overcomes the penetration/contrast bottleneck of imaging in the visible region, making it a remarkable modality for early diagnosis of cancer and highly sensitive tumor surgery. Due to their convenient bioconjugation with peptides/antibodies, NIR‐II molecular dyes are desirable candidates for targeted cancer imaging, significantly overcoming the autofluorescence/scattering issues for deep tissue molecular imaging. To promote the clinical translation of NIR‐II bioimaging, advancements in the high‐performance small molecule–derived probes are critically important. Here, molecules with clinical potential for NIR‐II imaging are discussed, summarizing the synthesis and chemical structures of NIR‐II dyes, chemical and optical properties of NIR‐II dyes, bioconjugation and biological behavior of NIR‐II dyes, whole body imaging with NIR‐II dyes for cancer detection and surgery, as well as NIR‐II fluorescence microscopy imaging. A key perspective on the direction of NIR‐II molecular dyes for cancer imaging and surgery is also discussed.