以昇陳

Nature Photonics, Published online: 25 March 2021; doi:10.1038/s41566-021-00783-1

Submicrometre-sized InGaN-based light-emitting diodes are fabricated by tailored ion implantation. The devices are free from electrical leakage and show a luminance of 7,440 nit at 4.9 A cm−2 even at the line/space scale of 0.5/0.5 μm (= 8,500 ppi).

The long aliphatic chains of aggregation‐induced emission (AIE)‐gens are conducive to the excretion of AIE dots from an animal's body. The deep micro cerebrovasculature in marmosets is visualized through the thinned skull. Non‐invasive and high‐spatial‐frequency near‐infrared‐IIb imaging is utilized in non‐human primates. It is believed this work provides crucial ideas to advance the development of biosafe AIE dots and future nanomedicine.

Abstract

Superb reliability and biocompatibility equip aggregation‐induced emission (AIE) dots with tremendous potential for fluorescence bioimaging. However, there is still a chronic lack of design instructions of excretable and bright AIE emitters. Here, a kind of PEGylated AIE (OTPA‐BBT) dots with strong absorption and extremely high second near‐infrared region (NIR‐II) PLQY of 13.6% is designed, and a long‐aliphatic‐chain design blueprint contributing to their excretion from an animal's body is proposed. Assisted by the OTPA‐BBT dots with bright fluorescence beyond 1100 nm and even 1500 nm (NIR‐IIb), large‐depth cerebral vasculature (beyond 600 µm) as well as real‐time blood flow are monitored through a thinned skull, and noninvasive NIR‐IIb imaging with rich high‐spatial‐frequency information gives a precise presentation of gastrointestinal tract in marmosets. Importantly, after intravenous or oral administration, the definite excretion of OTPA‐BBT dots from the body is demonstrated, which provides influential evidence of biosafety.

Ternary organic solar cells are fabricated, achieving a significant J _SC boost by virtue of an optimized crystalline feature with the formation of a eutectic mixture with better acceptor crystalline fibrils. The optimal morphology suppresses energetic disorder and recombination and increases charge transfer and transport, yielding a high efficiency of 17.84% with significant current boost.

Abstract

The intrinsic electronic properties of donor (D) and acceptor (A) materials in coupling with morphological features dictate the output in organic solar cells (OSCs). New physical properties of intimate eutectic mixing are used in nonfullerene-acceptor-based D–A₁–A₂ ternary blends to fine-tune the bulk heterojunction thin film morphology as well as their electronic properties. With enhanced thin film crystallinity and improved carrier transport, a significant J _SC amplification is achieved due to the formation of eutectic fibrillar lamellae and reduced defects state density. Material wise, aligned cascading energy levels with much larger driving force, and suppressed recombination channels confirm efficient charge transfer and transport, enabling an improved power conversion efficiency (PCE) of 17.84%. These results reveal the importance of utilizing specific material interactions to control the crystalline habit in blended films to form a well-suited morphology in guiding superior performances, which is of high demand in the next episode of OSC fabrication toward 20% PCE.

A chemical model capable of predicting the operational stability for organic light‐emitting devices is established, as reported by Dongho Kim, Jun Yeob Lee, Youngmin You, and co‐workers in article number 2003832. This model involves Langevin recombination, followed by electron transfer from a dopant to a host exciton, as the key degradation step. The research disentangles the chemical processes in the degradation and provides a useful foundation for enhancing the operational stability of electroluminescence devices.

An organic small-molecule semiconductor, DPh-DNTT, can be utilized as a dopant-free hole transporting material (HTM) for highly efficient and stable inverted perovskite solar cells due to its temperature-dependent molecular orientation. By decreasing the deposition temperature, DPh-DNTT films with a dominant face-on orientation are achieved, which exhibit improved out-of-plane hole mobility and excellent perovskite device performance without the incorporation of double-edged dopants.

Abstract

Crystallized p-type small-molecule semiconductors have great potential as an efficient and stable hole transporting materials (HTMs) for perovskite solar cells (PSCs) due to their relatively high hole mobility, good stability, and tunable highest occupied molecular orbitals. Here, a thienoacene-based organic semiconductor, 2,9-diphenyldinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DPh-DNTT), is thermally evaporated and employed as the dopant-free HTM that can be scaled up for large-area fabrication. By controlling the deposition temperature, the molecular orientation is modulated into a dominant face-on orientation with π–π stacking direction perpendicular to the substrate surface, maximizing the out-of-plane carrier mobility. With an engineered face-on orientation, the DPh-DNTT film shows an improved out-of-plane mobility of 3.3 × 10⁻² cm² V⁻¹ s⁻¹, outperforming the HTMs reported so far. Such orientation-reinforced mobility contributes to a remarkable efficiency of 20.2% for CH₃NH₃PbI₃ inverted PSCs with enhanced stability. The results reported here provide insights into engineering the orientation of molecules for the dopant-free organic HTMs for PSCs.

Small‐molecule organic solar cells based on a new electron donor reach power conversion efficiencies exceeding 13% with and without the use of electrode interlayers, but differ strongly in stability. Surprisingly, the surface composition and morphology of the interlayers deteriorate with time even under inert conditions, reducing device performance. Without interlayers, the cells give stable high performance.

Abstract

Electron transport layers (ETLs) placed between the electrodes and a photoactive layer can enhance the performance of organic solar cells but also impose limitations. Most ETLs are ultrathin films, and their deposition can disturb the morphology of the photoactive layers, complicate device fabrication, raise cost, and also affect device stability. To fully overcome such drawbacks, efficient organic solar cells that operate without an ETL are preferred. In this study, a new small‐molecule electron donor (H31) based on a thiophene‐substituted benzodithiophene core unit with trialkylsilyl side chains is designed and synthesized. Blending H31 with the electron acceptor Y6 gives solar cells with power conversion efficiencies exceeding 13% with and without 2,9‐bis[3‐(dimethyloxidoamino)propyl]anthra[2,1,9‐def:6,5,10‐d′e′f ′]diisoquinoline‐1,3,8,10(2H,9H)‐tetrone (PDINO) as the ETL. The ETL‐free cells deliver a superior shelf life compared to devices with an ETL. Small‐molecule donor–acceptor blends thus provide interesting perspectives for achieving efficient, reproducible, and stable device architectures without electrode interlayers.

A facile strategy of employing an acceptor‐analogue is developed to efficiently reduce trap density to a magnitude of 10¹⁵ cm⁻³ for organic photovoltaic materials, which is comparable to and even lower than those of some inorganic counterparts, and boosts the power conversion efficiency of organic solar cells up to 17.8%.

Abstract

Typical organic semiconductor materials exhibit a high trap density of states, ranging from 10¹⁶ to 10¹⁸ cm⁻³, which is one of the important factors in limiting the improvement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). In order to reduce the trap density within OSCs, a new strategy to design and synthesize an electron acceptor analogue, BTPR, is developed, which is introduced into OSCs as a third component to enhance the molecular packing order of electron acceptor with and without blending a polymer donor. Finally, the as‐cast ternary OSC devices employing BTPR show a notable PCE of 17.8%, with a low trap density (10¹⁵ cm⁻³) and a low energy loss (0.217 eV) caused by non‐radiative recombination. This PCE is among the highest values for single‐junction OSCs. The trap density of OSCs with the BTPR additives, as low as 10¹⁵ cm⁻³, is comparable to and even lower than those of several typical high‐performance inorganic/hybrid counterparts, like 10¹⁶ cm⁻³ for amorphous silicon, 10¹⁶ cm⁻³ for metal oxides, and 10¹⁴ to 10¹⁵ cm⁻³ for halide perovskite thin film, and makes it promising for OSCs to obtain a PCE of up to 20%.