Efficient inorganic perovskite light-emitting diodes (PeLEDs) with an ultrathin perovskite emission layer (∼30 nm) were realized by doping Lewis base polyethylene glycol (PEG) into CsPbBr3 films. PEG in the perovskite films not only physically fills the crystal boundaries but also interacts with the perovskite crystals to passivate the crystal grains, reduce nonradiative recombination, and ensure efficient luminance and high efficiency. As a result, promoted brightness, current efficiency (CE), and external quantum efficiency (EQE) were achieved. The nonradiative decay rate of the PEG:CsPbBr3 composite film is 1 order of magnitude less than that of the neat CsPbBr3 film. After further optimization of the molar ratio between CsBr and PbBr2, a peak CE of 19 cd/A, a maximum EQE of 5.34%, and a maximum brightness of 36600 cd/m2 were achieved, demonstrating the interaction between PEG and the precursors. The results are expected to offer some helpful implications in optimizing the polymer-assisted PeLEDs with ultrathin emission layers, which might have potential application in see-through displays.

Red-emissive solid-state carbon nanoparticles (CNPs) with a hollow sphere structure for white light-emitting diodes (WLEDs) were designed and synthesized by molecular self-assembly and microwave pyrolysis. Highly ordered graphite-like structures for CNPs were characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, and ultraviolet–visible (UV–vis) spectroscopy. The emission mechanism of the red-emissive solid-state CNPs was investigated in detail by steady-state and time-resolved photoluminescence (PL) spectroscopy. The as-prepared CNPs showed a red emission band centered at 620 nm with excitation wavelength independence, indicating uniform size of sp2 carbon domains in the CNPs. The CNPs also had a PL quantum yield (QY) of 17% under 380 nm excitation. Significantly, the PL QY of the organosilane-functionalized CNPs was 47%, which is the highest value recorded for red-emissive solid-state carbon-based materials under UV-light excitation. More importantly, the red-emissive CNPs exhibited a PL QY of 25% after storage in air for 12 months, indicating their excellent stability. The red-emissive CNP powders were used as environmentally friendly and low-cost phosphors on a commercial 460 nm blue GaN-based chip, and a pure white light with CIE coordinates of (0.35, 0.36) was achieved. The experimental results indicated that the red-emissive CNP phosphors have potential applications in WLEDs.Keywords: carbon nanoparticles, white light-emitting diodes, red emission; self-assembly, excitation wavelength-independent photoluminescence

Perovskite light-emitting diodes (PeLEDs) have attracted much attention in the past two years due to their high photo-luminescence quantum efficiencies and wavelength tuneable characteristics. In this work, the effect of annealing temperature and time on the perovskite (CH3NH3PbBr3) films and devices have been investigated in detail. The properties including photoluminescence, crystallinity and morphology of perovskite films together with device performance have been affected significantly by the annealing temperature and time. The PeLED with 80 °C annealing for 20 min shows the best device performance and exhibits a maximum luminance of 13700 cd m−2, and a maximum current efficiency of 8.22 cd A−1. This work will provide useful information for the future optimization and development in high quality perovskite films and high performance PeLEDs.

In this work, for the first time, thermal evaporated rubidium fluoride (RbF) and water-soluble RbF have been employed as the cathode interfacial layers (CILs) in inverted polymer solar cells (PSCs), respectively. The device with thermal evaporated RbF CIL exhibited a power conversion efficiency (PCE) of 6.41% when the thickness of RbF was 14 Å. A higher PCE of 6.82% was obtained in the aqueous RbF-based device, which is higher than that of a typical ZnO-CIL-based device (6.73%). More importantly, aqueous RbF opens a route to less poisonous, convenient, and low-cost processing CIL in inverted PSCs.

A multilayer transparent electrode WO3/Ag/WO3 (WAW) has been introduced into perovskite solar cells (PSCs). It is found that the substrate has an obvious effect on the perovskite morphology and crystallization and thus power conversion efficiency (PCE) of the PSCs. The precursor composition and its effect on the morphology, crystal, and device properties of the perovskite films based on WAW and ITO electrodes have been investigated in detail. When the CH3NH3I (MAI):PbI2 molar ratio is 1.04:1, the perovskite film shows flat and dense morphology formed by the complete reaction of MAI and PbI2, and PSC device shows the maximum PCE value of 9.73%, comparable with the controlled device with the MAI:PbI2 molar ratio of 1:1 based on ITO electrode (10.51%). Meanwhile, a flexible PSC based on WAW transparent electrode has also been fabricated, which exhibits a PCE of 8.04%, indicating that WAW multilayer transparent electrodes have the potential application in PSCs, especially in flexible PSCs.

A low-work-function, indium tin oxide (ITO)-free transparent cathode having a tin oxide (SnOX)/Ag/SnOX/bismuth oxide (Bi2O3) (SASB) structure is developed without using annealing treatment. This represents the first time that Bi2O3 has been introduced to lower the work function of transparent electrodes. The SASB transparent cathode exhibits excellent photoelectric properties with a maximum transmittance of ∼88%, a low sheet resistance of ∼9.0 Ω·sq–1, and a suitable work function of 4.22 eV that matches the lowest unoccupied molecular orbital level of the acceptor for exacting electrons efficiently. The power conversion efficiency of the polymer solar cell with the SASB electrode is 6.21%, which is comparable to that of ITO-based devices. The results indicate that SASB is a good alternative to ITO as transparent cathodes in optoelectronic devices.Keywords: bismuth oxide; ITO-free; polymer solar cell; transparent cathode; work function

Transparent electrodes with a dielectric–metal–dielectric (DMD) structure can be implemented in a simple manufacturing process and have good optical and electrical properties. In this study, nickel oxide (NiO) is introduced into the DMD structure as a more appropriate dielectric material that has a high conduction band for electron blocking and a low valence band for efficient hole transport. The indium-free NiO/Ag/NiO (NAN) transparent electrode exhibits an adjustable high transmittance of ∼82% combined with a low sheet resistance of ∼7.6 Ω·s·q–1 and a work function of 5.3 eV after UVO treatment. The NAN electrode shows excellent surface morphology and good thermal, humidity, and environmental stabilities. Only a small change in sheet resistance can be found after NAN electrode is preserved in air for 1 year. The power conversion efficiencies of organic photovoltaic cells with NAN electrodes deposited on glass and polyethylene terephthalate (PET) substrates are 6.07 and 5.55%, respectively, which are competitive with those of indium tin oxide (ITO)-based devices. Good photoelectric properties, the low-cost material, and the room-temperature deposition process imply that NAN electrode is a striking candidate for low-cost and flexible transparent electrode for efficient flexible optoelectronic devices.Keywords: flexible electronics; NiO; organic photovoltaic cells; transparent electrode