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This paper describes how a reversed-bias voltage affects organic light-emitting diodes (OLEDs) with green emitting \Alq3:C545T (40 nm). The luminance efficiency and the active area of the test OLED devices are 8–11 cd/A and 2.5 mm \times 2.5 mm, respectively. The OLED lifetime under an ac driving scheme can be apparently improved, in contrast with that under a dc driving scheme. Experimental results indicate that adjusting the duty ratio of the ac driving scheme can ameliorate the brightness uniformity; meanwhile, the normalized luminance of a 20% duty ratio after a 3600-s stress is 94.3%, and that of dc stress is 76.4%. Therefore, a novel pixel circuit with three p-type thin-film transistors (TFTs) for an active-matrix OLED application is proposed to ameliorate the brightness uniformity. Variations of the threshold voltage of the driving TFT are compensated for, and the performance and lifetime of the OLED are improved by using an ac driving method. Simulation results indicate that the output current is almost constant over the data range. Furthermore, the current error rate of the proposed pixel circuit is less than 6.5%. [ABSTRACT FROM AUTHOR]

This study presents a novel voltage-modulated pixel circuit for active-matrix organic light-emitting diode (AMOLED) consisting of five n-type thin-film transistors (TFTs), one additional control signal, and one storage capacitor. The proposed circuit, which can be implemented in all-n-type and all-p-type low temperature poly-silicon (LTPS) TFT technologies, successfully compensates for threshold voltage deviation of TFTs and facilitates correction of OLED degradation using a voltage feedback method. Simulation and experimental results for all-n-type TFTs indicate that the proposed pixel circuit reduced the nonuniformity brightness problem effectively by compensating for threshold voltage variation in TFTs and reduced the degradation of emission efficiency in OLEDs. [ABSTRACT FROM PUBLISHER]

This work presents a new pixel circuit using low‐temperature polycrystalline‐oxide thin‐film transistors (LTPO TFT) for active‐matrix organic light‐emitting diode (AMOLED) displays. The proposed circuit can compensate for the threshold voltage (Vth) variations of driving TFT. Moreover, the degradation of OLED can be reduced to a certain degree. The simulation results demonstrate that the current of OLED is independent of the Vth shifting and changes as the OLED threshold voltage. That means this LTPO circuit can improve the stability of displays. [ABSTRACT FROM AUTHOR]