Superficial fluoropolymer layers for efficient light-emitting diodes

• Published in: Organic electronics Vol. 13; no. 6; pp. 992 - 998
• Main Authors: Latini, Gianluca, Tan, Li Wei, Cacialli, Franco, Silva, S. Ravi P.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.06.2012; Elsevier
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electrode; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronics; Exact sciences and technology; Fluoropolymer; Interlayer; OLED; Optoelectronic devices; Physics; Polymer; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Surface double layers, schottky barriers, and work functions; Polymer; OLED; Electrode; Interlayer; Fluoropolymer; Interfacial layer; Performance evaluation; Interlayers; Anode; Photoluminescence; Thin film; Work function; Light emitting device; Thiophene derivative polymer; Optoelectronic device; Dipole; Organic electronics; Minority carrier; Polymer blends; Fluorine containing polymer; Active layer; Durability; Quantum yield; Light emitting diode; Quenching; Charge density; Solid state; Heterogeneous material; Luminance; Electrochemical properties; Heterogeneous medium; Styrenesulfonic acid polymer; Organic light emitting diodes; Styrenesulfonate polymer; Reliability
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2012.02.019

[Display omitted] ► This work is on the use of fluoropolymers in organic-based optoelectronic devices. ► The insertion of a PTFE interlayer results in an improved charge confinement. ► PTFE-based devices have been characterized and their efficiency results enhanced. ► PTFE behaves as a chemical zipper between two incompatible heterogeneous media. ► We observe an extended device longevity by a factor of 7. Fluoropolymers are characterized by high chemical inertness and, when in solid state, by superficial dipoles due to the C–F bond where the charge density is strongly displaced. These two characteristics are exploited here for fine control of charge balance in organic light-emitting devices and for preventing electrochemical interaction between heterogeneous layers. The insertion of a thin layer of polytetrafluoroethylene, PTFE, at the interface between poly(ethylene dioxythiophene):poly(styrene sulfonic acid), PEDOT:PSS, and an electroluminescent polymer leads to improved device efficiency and longevity. The presence of the superficial dipole increases the effective work function of the anode and improves the charge balance which enhances the external quantum efficiency, EQE, of the devices by up to a factor of two without significant effects on the luminance levels. The insertion of the PTFE layer reduces the photoluminescence quenching at the PEDOT:PSS/polymer interface, however we show that the EQE enhancement is mainly due to a better confinement of minority carrier electrons in the active layer. The lifetime of the devices shows a remarkable increase correlated with the insertion of the PTFE layer. Such improvements are ascribed to the reduced electrochemical interaction between the electroluminescent polymer and PEDOT:PSS due to the chemically inert nature of PTFE. The PTFE acts as a chemical zipper of two heterogeneous media with the added functionality of control over the charge balance.