Barium Hydroxide as an Interlayer Between Zinc Oxide and a Luminescent Conjugated Polymer for Light-Emitting Diodes (original) (raw)
Related papers
Reduced molybdenum oxide as an efficient electron injection layer in polymer light-emitting diodes
Applied Physics Letters, 2011
We report a significant improvement in the performance of single layer polymer light-emitting diodes ͑PLEDs͒, based on the green emitting copolymer poly͓͑9,9-dioctylfluorenyl-2,7-diyl͒co-͑1,4-benzo-͕2, 1Ј,3͖-thiadiazole͔͒, upon inserting a very thin layer of partially reduced molybdenum oxide ͑MoO x , where x = 2.7͒ at the polymer/Al cathode interface. Both fully oxidized ͑x=3͒ and partially reduced ͑x = 2.7͒ thin molybdenum oxide layers were investigated as electron injection layers and their influence on PLED device performance was examined. Improved current density, luminance, and efficiency was achieved only in the case of devices with a thin partially reduced MoO 2.7 film as electron injection layer, as a result of improved electron injection and more facile transfer at the modified polymer/Al interface.
ACS Applied Materials & Interfaces, 2015
The role of cathode buffer layer (CBL) is crucial in determining the power conversion efficiency (PCE) of inverted organic solar cells (IOSCs). The hallmarks of a promising CBL include high transparency, ideal energy levels and tendency to offer good interfacial contact with the organic bulk-heterojunction (BHJ) layers. Zinc oxide (ZnO), with its ability to form numerous morphologies in juxtapose to its excellent electron affinity, solution processability, and good transparency is an ideal CBL material for IOSCs. Technically, when CBL is sandwiched between the BHJ active layer and the indium-tin-oxide (ITO) cathode, it performs two functions viz, electron collection from the photoactive layer that is effectively carried out by morphologies like nanoparticles or nanoridges obtained by ZnO sol-gel (ZnO SG) method through an accumulation of individual nanoparticles and secondly, transport of collected electrons towards the cathode, which is more effectively manifested by 1D nanostructures like ZnO nanorods (ZnO NRs). This work presents the use of bilayered ZnO CBL in IOSCs of poly (3-hexylthiophene) (P3HT): [6, 6]-phenyl-C 60 -butyric acid methyl ester (PCBM) to overcome the limitations offered by a conventionally used single layer CBL. We found that the PCE of IOSCs with an appropriate bilayer CBL comprising of ZnO NRs-ZnO SG is ~18.21% higher than those containing ZnO SG-ZnO NRs. We believe that, in bilayer ZnO NRs-ZnO SG, ZnO SG collects electrons effectively from photoactive layer while ZnO NRs transport them further to ITO resulting significant increase in the photocurrent to achieve highest PCE of 3.70%. The enhancement in performance was obtained through improved interfacial engineering, enhanced electrical properties and reduced surface/bulk defects in bilayer ZnO NRs-ZnO SG. This study demonstrates that the novel bilayer ZnO CBL approach of electron collection/transport would overcome crucial interfacial recombination issues and contribute in enhancing PCE of IOSCs.
The Journal of Physical Chemistry C, 2014
Photoinduced charge separation at hybrid organic−inorganic interfaces is poorly understood and challenging to control. We investigate charge separation at a model system of ZnO/poly(3-hexylthiophene) (P3HT) and employ Sr doping of ZnO and phenyl-C61-butyric acid (PCBA) self-assembled modification to study and enhance the charge separation efficiency. We find that doping alone lowers the efficiency of charge separation due to the introduction of defect states at the oxide surface. However, with the combination of doping and molecular modification, charge separation efficiency is significantly enhanced due to the passivation of interfacial traps and improved modifier coverage. This demonstrates a complex noncumulative effect of doping and surface modification and shows that with the correct choice of metal oxide dopant and organic modifier, a poorly performing hybrid interface can be turned into an efficient one.
A study of tin oxide as an election injection layer in hybrid polymer light-emitting diodes
Semiconductor Science and Technology, 2014
We investigate the n-type metal oxide Tin (IV) oxide (SnO 2), as an electron injection and transport layer in hybrid polymer light-emitting diodes (HyLEDs). SnO 2 is air stable and biosafe, with high optical transparency and electrical conductivity, and with a deep valence band energy, making it highly suitable for such applications. Results reveal that SnO 2 is effective as an electron injecting cathode material, when a thin hole-blocking interlayer of Cs 2 CO 3 or Ba(OH) 2 is coated on it. Devices are optimized with respect to injection-layer thickness and hole-blocking layer configuration, with high performance metrics (current efficiencies of 20 cd/A, external quantum efficiencies of 6.5%) being demonstrated in the device with Ba(OH) 2 as the inorganic interlayer in the hybrid architecture. Also, we characterize thin-films of spray-pyrolysis deposited SnO 2 , as compared with the commonly used interlayer material ZnO, in terms of film morphology and interfacial photophysics.