Polyfluorene light-emitting devices and amorphous silicon:hydrogen TFT pixel circuits for active-matrix organic light-emitting displays.

摘要

Organic light-emitting devices (OLEDs) made of single-layer and double-layer polymer thin films have been fabricated and studied. The hole transporting (polymer A) and emissive (polymer B) polymers were poly(9,9′ -dioctyl fluorene-2,7-diyl)-co-poly(diphenyl-p-tolyl-amine-4,4 ′-diyl) and poly(9,9′-dioctyl fluorene-2,7-diyl)-co-poly(benzothiadiazole 2,5-diyl), respectively. The optical bandgaps of polymer A and B were 2.72 and 2.82 eV, respectively. The photoluminescence (PL) peaks for polymer A and B were 502 and 546 nm, respectively. The electroluminescence (EL) peak for polymer B was 547 nm. No EL has been observed from polymer A single layer OLEDs.; To obtain the spectral distribution of the emission properties of the light-emitting devices, a new light-output measurement technique was developed. Using this technique, the spectral distribution of the luminance, radiance, photon density emission can be obtained. Moreover, the device external quantum efficiency calculated using this technique is accurate and insensitive to the light emission spectrum shape.; Organic light-emitting devices have been fabricated and studied on both glass and flexible plastic substrates. The OLEDs showed a near-linear relationship between the luminance and the applied current density over four orders of magnitude. For the OLEDs fabricated on the glass substrate, luminance ∼9,300 cd/m2, emission efficiency ∼14.5 cd/A, luminescence power efficiency ∼2.26 lm/W, and external quantum efficiency ∼3.85% have been achieved. For the OLEDs fabricated on the flexible plastic substrates, both aluminum and calcium were used as cathode materials. The achieved maximum OLED luminance, emission efficiency, luminescence power efficiency, and external quantum efficiency were ∼13,000 cd/m2, ∼66.1 cd/A, ∼17.2 lm/W, and 16.7%, respectively.; To make an active-matrix organic light-emitting display (AM-OLED), a two-TFT pixel electrode circuit was designed and fabricated based on amorphous silicon TFT technology. This circuit was capable of providing continuous pixel excitation and a simple driving scheme. However, it showed an output current variation of ∼40% to 80% due to the drive TFT threshold voltage (V _th) shift after long-term operation. To improve the pixel circuit electrical reliability, a four-TFT pixel electrode circuit was proposed and fabricated. This circuit only showed an output current variation 1% for the high currents (>0.5μA) even when a TFT V_th shift as large as 3V was present. This four-TFT pixel electrode circuit was used to fabricate small size active-matrix monochrome organic light-emitting display.