8 October 2014 Two-color emission in three-layer heterostructure OLETs
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Two-color emission was observed in three-layer heterostructure organic light emitting transistors (OLETs). These devices consisted of a light-emitting layer made of tris(8-hydroxyquinolinato)aluminium (Alq3) doped with 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM), sandwiched between hole and electron transport layers made of α,ω-dihexyl-quaterthiophene (DH-4T) and α,ω-diperfluorohexyl-quaterthiophene (DFH-4T), respectively. Ambipolar transfer curves were recorded from the fabricated devices, and two-color emission (red and green) was observed during transfer curve acquisition. Red emission was observed to take place at bias conditions supporting hole transport, while green emission occurred when electron-based current was dominant. Moreover, red emission originated from the Alq3:DCM layer, which was verified by comparing the measured spectrum of OLETs to that of corresponding Alq3:DCM organic light-emitting diodes (OLEDs). To investigate the origin of green emission, OLETs were fabricated without an electron transport layer. No green emission was observed, while red emission remained unchanged. Moreover, single-layer transistors and diodes fabricated from DFH-4T expressed green color emission similar to that of three-layer heterostructure OLETs. Therefore, we suggest that green emission originates from the electron transport layer.
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K. Jokinen, K. Jokinen, A. Bykov, A. Bykov, T. Fabritius, T. Fabritius, R. Myllylä, R. Myllylä, "Two-color emission in three-layer heterostructure OLETs", Proc. SPIE 9183, Organic Light Emitting Materials and Devices XVIII, 91831Q (8 October 2014); doi: 10.1117/12.2060661; https://doi.org/10.1117/12.2060661

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