Increased conductivity of a hole transport layer due to oxidation by a molecular nanomagnet

Abstract

Thin film transistors based on polyarylamine poly͑N , NЈ-diphenyl-N , NЈbis͑4-hexylphenyl͒-͓1,1Јbiphenyl͔-4,4Ј-diamine ͑pTPD͒ were fabricated using spin coating in order to measure the mobility of pTPD upon oxidation. Partially oxidized pTPD with a molecular magnetic cluster showed an increase in mobility of over two orders of magnitude. A transition in the mobility of pTPD upon doping could also be observed by the presence of a maximum obtained for a given oxidant ratio and subsequent decrease for a higher ratio. Such result agrees well with a previously reported model based on the combined effect of dipolar broadening of the density of states and transport manifold filling. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2917304͔In recent years, there have been increasing interests and research activities in the field of organic light-emitting devices ͑OLEDs͒. The promise of the use of this technology in flat panel displays through the fabrication of low-cost and flexible electronic devices has been the main driving force. Although enormous progress has been achieved in improving the luminance efficiency, color fidelity, and device lifetime, there is a continuous effort for a better stability of the device toward commercialization. Interface engineering between the electrodes and the emitting layer is important for the improvement of the device lifetime as well as luminous efficiency in OLEDs and has lead to the fabrication of multilayer devices, with charge transport and charge injection layer ͑HIL͒ deposited by vacuum sublimation technique. 1,2 In terms of solution processable OLEDs, such as polymer based light emitting devices ͑PLEDs͒, the use of a PEDOT-PSS layer as the HIL is well known to improve the hole injection from the indium tin oxide ͑ITO͒ as well as planarizing the ITO surface and has been well studied. 3,4 Although it has shown improved device performance such as lower operational voltage and higher luminance efficiency, other problems render it not suitable for device stability. For example, it is found that the ITO/PEDOT-PSS interface is not stable due to the etching of ITO by the strong acidic nature of PSS. 5 Therefore, at this stage of PLED development, the search for other better solution processable HIL material is needed and it is much required to modify the HIL to further improve the device lifetime as well as its efficiency. Following such an approach, recent results by Bolink et al. 6 have shown that a solution processable HIL material can be used for PLEDs and showed improved performance as when using PEDOT-PSS. Such HIL material is based on a polyarylamine poly͑N , NЈ-diphenyl-N , NЈbis͑4-hexylphenyl͒-͓1,1Јbiphenyl͔-4,4Ј-diamine ͑pTPD͒ which was doped with a molecular magnet and showed tunable conductivity depending on the level of doping. The diamine derivative pTPD resembles very closely to the well known and intensively used organic molecule N , NЈ-diphenyl-N , NЈbis͑3-methylphenyl͒-͓1,1Јbiphenyl͔-4,4Ј-diamine ͑TPD͒, while being processable by the spin coating technique and...

Nanosecond‐Pulsed Perovskite Light‐Emitting Diodes at High Current Density

“…All devices were illuminated at one‐sun intensity (AM 1.5G, 100 mW cm −2 ) using a solar simulator for 15 min to photoactivate the n ‐dopant. [ 24 ] The device area is defined either by the overlap between ITO and Ag electrodes, or by a patterned insulating SiO 2 (120 nm) layer. All reported types of devices have been fabricated multiple times in at least two separate batches on different days.…”

“…While the IE and EA of poly‐TPD and PTAA are similar, poly‐TPD has a hole mobility around two orders of magnitude smaller than that of PTAA (2.4 × 10 −5 cm 2 V −1 s −1 ). [ 24 ] Figure 2a‐c presents some fundamental characterization of these PeLEDs. The current density ( J ) – voltage ( V ), EL spectra and angular‐dependent emission intensity profiles are shown in Figure S1, Supporting Information.…”