Electrical and Photoinduced Degradation of Polyfluorene Based Films and Light-Emitting Devices

Abstract

Degradation-induced changes in the structural and optical properties of the polyfluorene-based blue emitting films and LEDs are examined using spectroscopic (FTIR, UV−vis, photo- and electroluminescence), analytical (FTIR and ESCA), and scanning probe microscopy techniques. The materials studied are oligomers (DP ∼ 10) of 9,9-di-n-hexylfluorene and its random copolymer with anthracene. In situ FTIR monitoring is used to characterize chemical changes in the active layer of operating LED devices. Two primary mechanisms of degradation are identified. In the first, photooxidation of the polymer matrix leads to the formation of an aromatic ketone, most likely fluorenone at the chain terminating monomer units, which quenches the fluorescence. The second process promotes aggregate formation, which then leads to loss of luminous intensity by exciton transfer and relaxation through excimers.

ZnO-organic hybrid white light emitting diodes grown on flexible plastic using low temperature aqueous chemical method

“…28 Two justifications have been given for this green emission; one was the keto defect and the other was excimer. 28, 29 Lu et al 28 reported that green light will be emitted at high voltage as a result of the forma- 4. ͑Color online͒ ͑a͒ RT-PL spectrum of the ZnO NRs grown by the same parameters on plastic substrate with no PFO film.…”

Luminescence properties of poly(9,9-dioctylfluorene)/polyvinylcarbazole blends: Role of composition on the emission colour stability and electroluminescence efficiency

“…First studies attributed this emission to excimer states [8]. Later, the presence of fluorenone defects, formed by photooxidation or electrically induced at the C9 position of PFs, was held responsible for such emission [9].…”

Dispositivos poliméricos eletroluminescentes

“…Essa classe de polímeros, alguns dos quais estão mostrados na Figura 2, tem despertado o interesse dos estudiosos por suas propriedades elétricas e ópticas com potencial aplicação para fabricação de dispositivos emissores de luz (LEDs) [22][23][24][25][26][27][28][29][30][31][32][33] . Estes polímeros apresentam algumas propriedades interessantes para essa finalidade destacando-se, entre elas, grande estabilidade química, térmica e oxidativa 18,[34][35][36][37][38] ; alto rendimento quântico de fluorescência tanto em solução quanto no estado sólido 37,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57] ; possibilidade de formarem materiais líquido-cristalinos 46,[58][59][60][61][62][63][64]…”