Carriers injection and transport in small molecule organic light emitting diodes (OLED)

Our study focuses on the understanding of the mechanisms of charge injection and transport in small molecule organic light emitting diodes (OLED). One contribution of this work is the development of a new, indirect method to study carrier mobility in fabricated Alq3. The results from this method are consistent with those obtained from the large signal method, such as time of flight and transit delay time and no any thickness dependence of the carrier mobility was observed. Therefore, such modulation reduced the interface and trap charging effect due to its small signal nature, and complements the large signal method.; The electron mobility has been studied over temperature with a new modulation method which is effective for devices. An unexpected mobility maximum, correlated in temperature with the PL efficiency maximum and the onset of degradation in the EL efficiency, was observed. The EL efficiency (which combines mobility and charge balance terms) is attributed to the combination of a monotonically falling charge balance term with a PL efficiency maximum. The temperature dependent carriers transport mode is also investigated.; On the way to discussing mobility in organic devices, a number of studies were performed to optimize the performance of our thermally fabricated devices. Thin film device morphology was optimized. The EL performance of the green light OLED with various electrode structures is investigated and the brightness >1700cd/m2 and the EL efficiency >8cd/A in a thermally were obtained due to the enhancement of carrier injections resulted from the modified electrode structures. For the achievement of Full-color emission, red and blue light OLED were also fabricated and the dependence of the EL performance on the dopant and matrix organic layer were demonstrated.