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Molecular structures (a) of the materials used in preparation of film emitters and energy level diagram (b) of the donor (TPD) and acceptor [BPT; ] molecules forming emissive exciplexes. In addition to energy levels of the lowest unoccupied molecular orbitals (LUMO) and highest occupied molecular orbitals (HOMO) of organics, the Fermi level vacuum-referenced positions for ITO and Ca electrodes are given.
Absorption and emission spectra of -thick (a) single-active component films of TPD(40%):PC(60%) (solid lines), BPT(40%):PC(60%) (dashed lines), and (100%) (dotted lines) and (b) their blends as described in the text. Here and throughout all the work, the PL has been excited at .
Photocurrent (filled figures), and dark current (open figures) as functions of applied field with the injection forward ITO(+) and reversed ITO(−) electrode bias for the phosphorescent and fluorescent TPD:BPT blend films.
Left-hand ordinate: the PL quenching as a function of applied electric field for two different composition films and electrical bias electrodes as described in the figure. Right-hand ordinate: the high-field range (from ) vs plots extracted according to Eq. (3) from the experimental values of (left-hand ordinate) for two limiting cases, (crosses) and (diamonds), where is the factor scaling the Poole-Frenkel-type field dependence of the mobility . Its best fit (diamonds) to the straight-line plot of (solid line) is obtained with (, ), , , and a field dependent with .
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