Tham khảo tài liệu 'organic light emitting diodeedited by marco mazzeosciyo part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Material Issues in AMOLED 47 results are summarized in Table 1 with the well-known hole-transporting material HTM 1 for comparison. As shown in Table 1 all three phenylnaphthyldiamine-cored HTMs HTM 2-4 have higher value of Tg relative to their biphenyldiamine analog HTM 1 proofing the high morphologic stability of the amorphous phase in a deposited film which is a prerequisite for the application in organic electroluminescent devices. According to Shirota 1 a non-planar molecular structure preventing easy packing of molecules and an increased number of conformers in the molecule are preconditions in the design and synthesis of amorphous molecular glasses. Glass formation is enhanced by incorporation of bulky substituents. The incorporation of bulky substituents also hinders translational rotational and vibrational motions of molecules leading to an increase in the Tg. We attribute to the increase in the morphological stability of the biphenyl-based material to the presence of naphthalene substituents at the central phenylnaphthyl core which may hinder the crystallization process. It is important that OLEDs be constructed from materials having a relatively high value of Tg to avoid problems associated with crystallization which leads to device degradation. The HOMO and LUMO levels of these phenylnaphthyldiamine derivatives are also listed in Table 1. The HOMO was determined using a photoelectron spectrometer while LUMO was calculated based on the HOMO energy level and the lowest energy absorption edge of the UV absorption spectrum. The HOMO and LUMO levels of these compounds were measured at ca. - eV and - respectively. Compounds Tda C Tgb C Tmb C Tcb C Ấmaxc nm HOMOd eV LUMOe eV HTM 1 380 121 264 NA 360 HTM 2 395 159 296 NA 342 HTM 3 430 167 225 NA 355 HTM 4 423 174 255 NA 353 a Obtained from TGA measurement. b Obtained from DSC measurement. c Measured in CH2Cl2 solution. d Determined by ultraviolet .
