Perovskite light‐emitting diodes (PeLEDs) are emerging candidates for the applications of solution‐processed full‐color displays. However, the device performance of deep‐blue PeLED still lags far behind that of their red and green counterparts, which is largely limited by low external quantum efficiency (EQE) and poor operational stability. Here, a facile and reliable crystallization strategy for perovskite grains is proposed, with improved deep‐blue emission through rational interfacial engineering. By modifying the substrate with potassium cation (K+) as the supplier of heterogeneous nucleation seeds, the interfacial K+‐guided grain growth is realized for well‐packed perovskite assemblies with high surface coverage and the controlled crystal orientation, leading to the enhanced radiative recombination and hole‐transport capabilities. Synergistical boost in device performance is achieved for deep‐blue PeLEDs emitting at 469 nm with a peak EQE of 4.14%, a maximum luminance of 451 cd m–2, and spectrally stable color coordinates of (0.125, 0.076) that matches well with the National Television System Committee (NTSC) standard blue.

The on-surface polymerization of 1,3,6,8-tetrabromopyrene (Br4 Py) on Cu(111) and Au(111) surfaces under ultrahigh vacuum conditions was investigated by a combination of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Deposition of Br4 Py on Cu(111) held at 300 K resulted in a spontaneous debromination reaction, generating the formation of a branched coordination polymer network stabilized by C-Cu-C bonds. After annealing at 473 K, the C-Cu-C bonds were converted to covalent C-C bonds, leading to the formation of a covalently linked molecular network of short oligomers. In contrast, highly ordered self-assembled two-dimensional (2D) patterns stabilized by both Br-Br halogen and Br-H hydrogen bonds were observed upon deposition of Br4 Py on Au(111) held at 300 K. Subsequent annealing of the sample at 473 K led to a dissociation of the C-Br bonds and the formation of disordered metal-coordinated molecular networks. Further annealing at 573 K resulted in the formation of covalently linked disordered networks. Importantly, we found that the chosen substrate not only plays an important role as catalyst for the Ullmann reaction, but also influences the formation of different types of intermolecular bonds and thus, determines the final polymer network morphology. DFT calculations further support our experimental findings obtained by STM and XPS and add complementary information on the reaction pathway of Br4 Py on the different substrates.

PSS-GO:NH3 layer, and partially to the better matched energy-level-alignment at the perovskite interface. Furthermore, the device was shown to be more stable in the ambient condition, which is clearly associated with the improved peovskite structure stability by the GO:NH3 layer observed by the GIXRD measurements. All these achievements will promote more applications of chemically modified graphene oxide interfacial layer in the PSCs as well as other organic multilayer devices.

Rubidium adsorption on the surface of the topological insulator Bi(2)Se(3) is found to induce a strong downward band bending, leading to the appearance of a quantum-confined two-dimensional electron gas state (2DEG) in the conduction band. The 2DEG shows a strong Rashba-type spin-orbit splitting, and it has previously been pointed out that this has relevance to nanoscale spintronics devices. The adsorption of Rb atoms, on the other hand, renders the surface very reactive, and exposure to oxygen leads to a rapid degrading of the 2DEG. We show that intercalating the Rb atoms, presumably into the van der Waals gaps in the quintuple layer structure of Bi(2)Se(3), drastically reduces the surface reactivity while not affecting the promising electronic structure. The intercalation process is observed above room temperature and accelerated with increasing initial Rb coverage, an effect that is ascribed to the Coulomb interaction between the charged Rb ions. Coulomb repulsion is also thought to be responsible for a uniform distribution of Rb on the surface.

The adsorption behaviour as well as the influence of bromine substituents on the formation of highly-ordered two-dimensional structures of pyrene derivatives on Au(111) are studied by a combination of scanning tunnelling microscopy (STM) and density functional theory (DFT) calculations.

Efficient and stable blue emission of perovskite light-emitting diodes (PeLEDs) is a requisite toward their potential applications in full-color displays and solid-state lighting. Rational manipulation over the entire electroluminescence process is promising to break the efficiency limit of blue PeLEDs. Herein, a facile device architecture is proposed to achieve efficient blue PeLEDs for simultaneously reducing the energetic loss during electronphoton conversion and boosting the light outcoupling. Effective interfacial engineering is employed to manipulate the perovskite crystallization nucleation, enabling highly compact perovskite nanocrystal assemblies and suppressing the trap-induced carrier losses by means of interfacial hydrogen bonding interactions. This strategy contributes to a high external quantum efficiency (EQE) of 12.8% for blue PeLEDs emitting at 486 nm as well as improved operational stability. Moreover, blue PeLEDs reach a peak EQE of 16.8% with the incorporation of internal outcoupling structures for waveguided light, which can be further raised to 27.5% by integrating a lensbased structure for substrate-mode light. These results verify the validity of this strategy in producing efficient and stable blue PeLEDs for practical applications.

The electronic structures of rubrene films deposited on CHNHPbI perovskite have been investigated using in situ ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It was found that rubrene molecules interacted weakly with the perovskite substrate. Due to charge redistribution at their interface, a downward 'band bending'-like energy shift of ∼0.3 eV and an upward band bending of ∼0.1 eV were identified at the upper rubrene side and the CHNHPbI substrate side, respectively. After the energy level alignment was established at the rubrene/CHNHPbI interface, its highest occupied molecular orbital (HOMO)-valence band maximum (VBM) offset was found to be as low as ∼0.1 eV favoring the hole extraction with its lowest unoccupied molecular orbital (LUMO)-conduction band minimum (CBM) offset as large as ∼1.4 eV effectively blocking the undesired electron transfer from perovskite to rubrene. As a demonstration, simple inverted planar solar cell devices incorporating rubrene and rubrene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) hole transport layers (HTLs) were fabricated in this work and yielded a champion power conversion efficiency of 8.76% and 13.52%, respectively. Thus, the present work suggests that a rubrene thin film could serve as a promising hole transport layer for efficient perovskite-based solar cells.

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