Laminated low-melting-point-alloy electrodes for vacuum-free-processed quantum-dot light-emitting-diodes

Abstract

Quantum-dot light-emitting-diodes (QLEDs) can be fabricated by low-cost solution processes, such as spin-coating or inkjet printing, making them strong rivals to their organic LED counterparts. However, the top electrodes, which are usually based on metallic thin-films, such as Al or Ag, have to be deposited by a costly vacuum process, which is incompatible with the low-cost solution process. In this work, an InSnBi alloy, which has a low-melting-point of 47 °C, is developed as a laminated top cathode for the QLEDs. Because of the presence of the native oxides that serve as an electron blocking layer, the resultant vacuum-free fabricated QLEDs exhibit an improved performance, with a peak external quantum efficiency of 12.3%, 9.15%, and 2.5% for red, green, and blue devices, respectively, which is 1.5-, 1-, and 1.1-fold higher than that of QLEDs with evaporated Al cathodes. The elimination of the costly vacuum process allows rapid high throughput, and low-cost fabrication of QLEDs for material screening purpose.

Fusible Low Work Function Top Electrode for Vacuum-Free Perovskite Light-Emitting Diode Application: Role of OH-Terminated Sn Atoms at the Alloy Surface

“…Figure a–e depicts the XPS spectra of Bi, In, Sn, and Pb elements. As can be seen in Figure b–d, the elemental XPS spectra of Bi, In, and Pb depict multiple peaks such as Bi 4f 7/2 , 4f 5/2 , 5s; In 3d 5/2 , 3d 3/2 ; and Pb 4f 7/2 , 4f 5/2 , respectively, which result from the spin–orbit interaction . Therefore, the Bi, In, and Pb elements in LMPA composition exist in the metallic state.…”

“…However, the XPS spectrum of Sn exhibits four peaks which are metallic 3d 5/2 , 3d 3/2 and oxidized 3d 5/2 , 3d 3/2 centered at 484.2, 492.4 eV and 485.85, 494.35 eV, respectively (Figure e). The presence of oxidized Sn 3d 5/2 and Sn 3d 3/2 indicate that a part of Sn is oxidized and forms SnO . Recently, Xia et al demonstrated that the presence of the native oxides in oxidized Sn could serve as an electron blocking layer in the quantum-dot light-emitting diodes (QLEDs), which improve the charge balance injection as well as stability of the devices. , …”

“…The presence of oxidized Sn 3d 5/2 and Sn 3d 3/2 indicate that a part of Sn is oxidized and forms SnO . Recently, Xia et al demonstrated that the presence of the native oxides in oxidized Sn could serve as an electron blocking layer in the quantum-dot light-emitting diodes (QLEDs), which improve the charge balance injection as well as stability of the devices. , …”

“…Therefore, these materials could dissolve underneath layers in the device structure. To avoid dissolution of underneath layers, people have used several low melting point solvent free alloys in quantum dot light-emitting diodes. , These low melting point alloys (LMPAs) expect to have work functions in the range 4.2–4.3 eV with limited experimental evidence . A general strategy for high-efficiency p–i–n structured perovskite device fabrication is to use low work function top electrodes which should match with the LUMO level of the electron transport materials.…”

“…32,33 These low melting point alloys (LMPAs) expect to have work functions in the range 4.2−4.3 eV with limited experimental evidence. 33 A general strategy for high-efficiency p−i−n structured perovskite device fabrication is to use low work function top electrodes which should match with the LUMO level of the electron transport materials. Calcium having a work function ∼2.9 eV becomes the obvious choice, albeit very poor environmental stability.…”