Inkjet-Printed Full-Color Matrix Quasi-Two-Dimensional Perovskite Light-Emitting Diodes.

Full-color matrix devices based on perovskite light-emitting diodes (PeLEDs) formed via inkjet printing are increasingly attractive due to their tunable emission, high color purity, and low cost. A key challenge for realizing PeLED matrix devices is achieving high-quality perovskite films with a favorable emission structure via inkjet printing techniques. In this work, a narrow phase distribution, high-quality quasi-two-dimensional (quasi-2D) perovskite film without a "coffee ring" was obtained via the introduction of a phenylbutylammonium cation into the perovskite and the use of a vacuum-assisted quick-drying process. Relatively efficient emissions of red, green, and blue (RGB) uniform quasi-2D perovskite films with high photoluminescence quantum yields were cast by the inkjet printing technique. The RGB monochrome perovskite matrix devices with 120 pixel-per-inch resolution exhibited electroluminescence, with maximum external quantum efficiencies of 3.5, 3.4, and 1.0% (for red, green, and blue light emissions, respectively). Furthermore, a full-color perovskite matrix device with a color gamut of 102% (NTSC 1931) was realized. To the best of our knowledge, this is the first report of a full-color perovskite matrix device formed by inkjet printing.

Effects of ZnMgO Electron Transport Layer on the Performance of InP-Based Inverted Quantum Dot Light-Emitting Diodes.

An environment-friendly inverted indium phosphide red quantum dot light-emitting diode (InP QLED) was fabricated using Mg-doped zinc oxide (ZnMgO) as the electron transport layer (ETL). The effects of ZnMgO ETL on the performance of InP QLED were investigated. X-ray diffraction (XRD) analysis indicated that ZnMgO film has an amorphous structure, which is similar to zinc oxide (ZnO) film. Comparison of morphology between ZnO film and ZnMgO film demonstrated that Mg-doped ZnO film remains a high-quality surface (root mean square roughness: 0.86 nm) as smooth as ZnO film. The optical band gap and ultraviolet photoelectron spectroscopy (UPS) analysis revealed that the conduction band of ZnO shifts to a more matched position with InP quantum dot after Mg-doping, resulting in the decrease in turn-on voltage from 2.51 to 2.32 V. In addition, the ratio of irradiation recombination of QLED increases from 7% to 25% using ZnMgO ETL, which can be attributed to reduction in trap state by introducing Mg ions into ZnO lattices. As a result, ZnMgO is a promising material to enhance the performance of inverted InP QLED. This work suggests that ZnMgO has the potential to improve the performance of QLED, which consists of the ITO/ETL/InP QDs/TCTA/MoO3/Al, and Mg-doping strategy is an efficient route to directionally regulate ZnO conduction bands.

Bifacial passivation towards efficient FAPbBr3-based inverted perovskite light-emitting diodes.

A unique technique to passivate both bottom and top sides of perovskite has been successfully developed to achieve highly efficient inverted perovskite light-emitting diodes (PeLEDs). For the bottom passivation, an organic/inorganic hybrid electron transporting layer (ETL) replaces the widely adopted inorganic ETL to overcome the disadvantages of the pure inorganic ETL. The ZPM (ZnO-in-polymer matrix) ETL, which consists of ZnO nanoparticles blended into polyvinylpyrrolidone, not only passivates the surface defects of ZnO nanoparticles, but also improves the morphology and stability of FAPbBr3 film. For the top passivation, smaller grains and a FAPbBr3/PEA2PbBr4 3D/2D hybrid structure are obtained by applying a small amount of PEABr solution. The synergetic interplay of organic/inorganic hybrid ETL and organic halide salt surface modification substantially shrinks the grain size to facilitate radiative recombination, and suppresses non-radiative recombination both at the interface of ETL/perovskite and HTL/perovskite, and in the perovskite layer. As a result, the highly efficient green PeLED sets a new record of device performance for FAPbBr3-based inverted PeLEDs, with current efficiency of 39.7 cd A-1, external quantum efficiency of 9.0%, power efficiency of 46.4 lm W-1, maximum luminance of 6.03 × 104 cd m-2, and half-lifetime of 297 minutes at an initial brightness of ∼100 cd m-2.

Rationally Controlled Synthesis of CdSexTe1-x Alloy Nanocrystals and Their Application in Efficient Graded Bandgap Solar Cells.

CdSexTe1-x semiconductor nanocrystals (NCs), being rod-shaped/irregular dot-shaped in morphology, have been fabricated via a simple hot-injection method. The NCs composition is well controlled through varying molar ratios of Se to Te precursors. Through changing the composition of the CdSexTe1-x NCs, the spectral absorption of the NC thin film between 570-800 nm is proved to be tunable. It is shown that the bandgap of homogeneously alloyed CdSexTe1-x active thin film is nonlinearly correlated with the different compositions, which is perceived as optical bowing. The solar cell devices based on CdSexTe1-x NCs with the structure of ITO/ZnO/CdSe/CdSexTe1-x/MoOx/Au and the graded bandgap ITO/ZnO/CdSe(w/o)/CdSexTe1-x/CdTe/MoOx/Au are systematically evaluated. It was found that the performance of solar cells degrades almost linearly with the increase of alloy NC film thickness with respect to ITO/ZnO/CdSe/CdSe0.2Te0.8/MoOx/Au. From another perspective, in terms of the graded bandgap structure of ITO/ZnO/CdSe/CdSexTe1-x/CdTe/MoOx/Au, the performance is improved in contrast with its single-junction analogues. The graded bandgap structure is proved to be efficient when absorbing spectrum and the solar cells fabricated under the structure of ITO/ZnO/CdSe0.8Te0.2/CdSe0.2Te0.8/CdTe/MoOx/Au indicate power conversion efficiency (PCE) of 6.37%, a value among the highest for solution-processed inversely-structured CdSexTe1-x NC solar cells. As the NC solar cells are solution-processed under environmental conditions, they are promising for fabricating solar cells at low cost, roll by roll and in large area.

Solvent Engineering for High-Performance PbS Quantum Dots Solar Cells.

PbS colloidal quantum dots (CQDs) solar cells have already demonstrated very impressive advances in recent years due to the development of many different techniques to tailor the interface morphology and compactness in PbS CQDs thin film. Here, n-hexane, n-octane, n-heptane, isooctane and toluene or their hybrids are for the first time introduced as solvent for comparison of the dispersion of PbS CQDs. PbS CQDs solar cells with the configuration of PbS/TiO2 heterojunction are then fabricated by using different CQDs solution under ambient conditions. The performances of the PbS CQDs solar cells are found to be tuned by changing solvent and its content in the PbS CQDs solution. The best device could show a power conversion efficiency (PCE) of 7.64% under AM 1.5 G illumination at 100 mW cm-2 in a n-octane/isooctane (95%/5% v/v) hybrid solvent scheme, which shows a ~15% improvement compared to the control devices. These results offer important insight into the solvent engineering of high-performance PbS CQDs solar cells.

CdTe Nanocrystal Hetero-Junction Solar Cells with High Open Circuit Voltage Based on Sb-doped TiO2 Electron Acceptor Materials.

We propose Sb-doped TiO2 as electron acceptor material for depleted CdTe nanocrystal (NC) hetero-junction solar cells. Novel devices with the architecture of FTO/ZnO/Sb:TiO2/CdTe/Au based on CdTe NC and TiO2 precursor are fabricated by rational ambient solution process. By introducing TiO2 with dopant concentration, we are able to tailor the optoelectronic properties of NC solar cells. Our novel devices demonstrate a very high open circuit voltage of 0.74 V, which is the highest Voc reported for any CdTe NC based solar cells. The power conversion efficiency (PCE) of solar cells increases with the increase of Sb-doped content from 1% to 3%, then decreases almost linearly with further increase of Sb content due to the recombination effect. The champion device shows Jsc, Voc, FF, and PCE of 14.65 mA/cm², 0.70 V, 34.44, and 3.53% respectively, which is prospective for solution processed NC solar cells with high Voc.