Three Destinies of Solution-Processable Polymer Light-Emitting Diodes under Long-Time Operation

Abstract

The article describes three different ways of polymer light-emitting diode (PLED) degradation, caused by damage of the protective layer. The electroluminescence and charge-transport properties of a completely encapsulated diode, the diodes with a leaky protective layer and diodes without encapsulation were compared under long-time exploitation. The studied devices incorporated Super Yellow light-emitting poly-(1,4-phenylenevinylene) PPV copolymer as an electroluminescence component, and (poly-(3,4-ethylenedioxythiophene)–poly-(styrene sulfonate) (PEDOT:PSS) as a charge-transport layer between the indium tin oxide (ITO) anode and aluminum–calcium cathode. To analyze the PLED degradation mechanism regarding charge transport, impedance spectroscopy was used. The values of resistance and capacitance of the internal layers revealed an effect of applied voltage on charge carrier injection and recombination. The factors responsible for the device degradation were analyzed on a macromolecular level by comparing the plots of voltage dependence of resistance and capacitance at different operation times elapsed.

Room-Temperature Photodeposited Amorphous VOx Hole-Transport Layers for Organic Devices

“…In both cases, the work function values are close to the ITO work function, reported to be between 4.4 and 4.8 eV . Similarly, these are also close to the HOMO level of the active layer used; the value for super yellow is reported between 5.1 and 5.4 eV , while PM6:Y6 is generally said to have its HOMO in between 5.5 and 5.7 eV. ,, This allows the VO x layer, with its intermediate value of around 5 eV, to act as an efficient hole transfer layer between the active layer and the ITO. This has a significant impact on OLED devices, where a low turn-on voltage is favored by sufficient conductivity and suitable work function that facilitate the injection of holes from the anode and the transfer of those holes into the emission layer. , The work function of the VO x films is close to the ITO work function and the HOMO level of the active layer, super yellow.…”

“…In both cases, the work function values are close to the ITO work function, reported to be between 4.4 and 4.8 eV. 54 Similarly, these are also close to the HOMO level of the active layer used; the value for super yellow is reported between 5.1 and 5.4 eV 55,56 while PM6:Y6 is generally said to have its HOMO in between 5.5 and 5.7 eV. 32,57,58 This allows the VO x layer, with its intermediate value of around 5 eV, to act as an efficient hole transfer layer between the active layer and the ITO.…”

Room-temperature photodeposited amorphous VOx hole-transport layers for organic devices

“…superyellow is reported between 5.1-5.4 eV 40,41 while PM6:Y6 is generally said to have its HOMO in between 5.5-5.7 eV. 27,42,43 This allows the VO x layer, with its intermediate value of around 5 eV, to act as efficient hole transfer layer between the active layer and the ITO.…”

Hofmeister Series for Conducting Polymers: The Road to Better Electrochemical Activity?

“…The use of PEDOT:PSS aqueous dispersions has proven to be very attractive for producing films of varying thicknesses on both conductive and non-conductive substrates, and has opened up the possibility of using many common coating and printing techniques such as drop casting, spin coating, spray coating, inkjet printing, and screen printing. These advantages have made PEDOT:PSS one of the most commercially successful conducting polymers [3] and it is now actively used in solar cells [4][5][6], LEDs [7,8], field effect transistors [9], thermoelectric devices [10,11], electrochromic devices [12], and sensors [13].…”