Near‐infrared organic light‐emitting diodes (NIR OLEDs) enable many unique applications ranging from night‐vision displays and photodynamic therapies. However, the development of efficient NIR OLEDs with a low efficiency roll‐off is still challenging. Here, a series of new heteroleptic Pt(II) complexes (1–4) flanked by both pyridyl pyrimidinate and functional azolate chelates are synthesized. The reduced ππ* energy gap of the pyridyl pyrimidinate chelate, and strong intermolecular interaction and high crystallinity in vacuum‐deposited thin films engender strong intermolecular charge transfer transition including metal–metal‐to‐ligand charge transfer; thereby, exhibiting efficient photoluminescence within 776–832 nm and short radiative lifetimes of 0.52–0.79 µs. Consequently, nondoped NIR‐emitting OLEDs based on these Pt(II) complexes are fabricated, to which Pt(II) complexes 2 and 4 give record high maximum external quantum efficiency of 10.61% at 794 nm and 9.58% at 803 nm, respectively. Moreover, low efficiency roll‐off is also observed, among which the device efficiencies of 2 and 4 are at least four times higher than that of the best NIR‐emitting OLEDs recorded at current density of 100 mA cm−2.
Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) has been used for gaining insights into perovskite solar cells (PSCs). However, the importance of selecting ion beam parameters to eliminate artifacts in the resulting depth profile is often overlooked. In this work, significant artifacts were identified with commonly applied sputter sources, i.e., an O 2 + beam and an Ar-gas cluster ion beam (Ar-GCIB), which could lead to misinterpretation of the PSC structure. On the other hand, polyatomic C 60 + and Ar + ion beams were found to be able to produce depth profiles that properly reflect the distribution of the components. On the basis of this validated method, differences in component distribution, depending on the fabrication processes, were identified and discussed. The solvent-engineering process yielded a homogeneous film with higher device performance, but sequential deposition led to a perovskite layer sandwiched by methylammonium-deficient layers that impeded the performance. For device degradation, it was found that most components remained intact at their original position except for iodide. This result unambiguously indicated that iodide diffusion was one of the key factors governing the device lifetime. With the validated parameters provided, ToF-SIMS was demonstrated as a powerful tool to unveil the structure variation amid device performance and during degradation, which are crucial for the future development of PSCs.
PtPd nanocrystals (NCs) with various alloying compositions are strategically prepared through the chemical method and exploited as counter electrodes (CEs) in dyesensitized solar cells (DSSCs). The photovoltaic results unveil the composition-dependent trend with a volcano-shaped plot of
Interlayer charge-transfer (CT) excitons in heterostructures are of great importance because of their crucial roles in manipulating the device performance and many-body quantum behaviors. Nonetheless, enigmas arise in organic/inorganic heterointerfaces because localized excitons and inhomogeneity in organic materials hinder the interlayer CT processes. Here, we demonstrate that the interlayer CT excitons form in the new organic/inorganic heterostructure composed by the Pt(II) complex 4Me and monolayered transition-metal dichalcogenide PtSe 2 . The "edge-on" alignment of 4Me is resolved by high-resolution transmission electron microscopy and grazing-incidence X-ray diffraction. Photoelectron spectroscopies verify that the interlayer CT was promoted by the type-II energy band alignment. Moreover, steady-state vis/NIR spectroscopy captures the interlayer CT optical transition and transient absorption spectroscopies unveil the fast charge separation (0.4 ps) coupled with the out-of-plane acoustic phonon mode (0.40 THz) from the PtSe 2 monolayer, followed by the slow charge recombination (0.86 μs). This work systematically characterizes the morphology of the 2D heterointerface and the photophysical mechanism of interlayer CT processes, which expand the vision of the material design in organic/inorganic heterostructures and monolayer-based devices.
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