Electroluminescence and photoluminescence in poly(di- n-octylfluorene) light-emitting diodes operated at elevated temperatures

• Published in: Synthetic metals Vol. 154; no. 1; pp. 137 - 140
• Main Authors: Cheun, H., Winokur, M.J.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Lausanne Elsevier B.V 22-09-2005; Amsterdam Elsevier Science; New York, NY
• Subjects: Application fields; Applied sciences; Electroluminescence; Electronics; Exact sciences and technology; Liquid crystalline phase; Optoelectronic devices; Other conjugated and/or conducting polymers; Photoluminescence; Polymer industry, paints, wood; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Technology of polymers; Liquid crystalline phase; Other conjugated and/or conducting polymers; Electroluminescence; Photoluminescence; Voltage current curve; Thermotropic state; Aromatic polymer; Thermal cycle; Temperature effect; Fluorene derivative polymer; Experimental study; Light emitting diode; Conjugated polymer; Liquid crystal polymers; Optical properties; Current time characteristic
• ISSN: 0379-6779; 1879-3290
• DOI: 10.1016/j.synthmet.2005.07.035

Both electroluminescence (EL) and photoluminescence from conventional poly(di-
n-octylfluorene) (PF8) light emitting diodes (LEDs) has been monitored
in situ during thermal cycling at temperatures up to 410
K. Even after the PF8 polymer undergoes a thermotropic phase transition to a liquid crystal phase these LEDs continue to operate although at reduced currents. This behavior is likely caused by changes in the hole transport layer and/or polymer interfaces and not by the phase transition itself. Overall EL output is diminished but PL measurements indicate no evidence of PF8 degradation. The step-wise thermal cycling of a working device produces a decrease in the relative EL efficiency at higher applied bias voltages but results in a pronounced EL efficiency increase at voltages near the device turn-on threshold. EL emission and measured device currents are both time- and temperature-dependent.