| Summary: | 碩士 === 國立清華大學 === 光電工程研究所 === 94 === We measure the delay time using the time-resolved electroluminescence (EL) technology by the time-correlated single photon counting system. We calculate the mobility of the organic material based on the delay time at various applied voltages.
We find that by using an exponential function to fit the measured transient fluorescence, delay time independent of the counting rates can be obtained. With delay time extracted in the way, better estimate of the mobility can be obtained.
In single layer structure, we find that the light emitting due to the defects has the shorter delay time than that due to the singlet exciton. Furthermore, we study the delay time and the mobility of the organic material by changing the processing conditions such as the solvent, the emission layer area, the emission layer thickness and the cathode materials. We find that: (1) the use of xylene as solvent of the emission layer leads to shorter delay than THF. (2) the larger the emission area is, the longer the delay time is. This is attributed to the larger area results in the longer RC delay. However the emission area dosen’t affect the carrier mobility. (3) thicker light emission layer shows higher mobility and shorter RC delay; hence leading to the shorter delay time. (4) different cathode materials (Ca/Al, CsF/Al, and LiF/Ca/Al) results in different mobilities, and the devices evaporated on the cathode, LiF/Ca/Al,
shows the highest mobility.
In bilayer structure, we also find that the mobility is thickness dependent. However, some of the difficulties in the mobility study based on the bilayer or
multilayer structure remained unsolved; further investigation is required.
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