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16 April 2008 Cathode effect on current-voltage characteristics of blue light-emitting diodes based on a polyspirofluorene
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Abstract
Current-voltage characteristics of polyspiroblue SB -based light-emitting diodes with the structure: ITO/PEDOT:PSS/SB/cathode have been analyzed. Several cathodes were used (Al, LiF with different thicknesses, and Ba) in order to change the barrier for electron injection. As expected, the inclusion of a thin (0.5-1 nm) LiF layer between SB and Al, or the use of Ba, modifies the electron barrier as derived from the increment in the turn-on voltage (related to the built-in potential) with respect to that observed for Al cathode. For hole-only devices (Au cathode) J-V characteristics are interpreted in terms of bulk-limited SCLC transport with hole mobility of the order of 10-6 cm2/V s. When J-V characteristics obtained using different cathodes are compared the current level observed are consistent with the mobility observed for the hole only device. This implies that the device operation is mainly determined by the hole conduction. However, the electroluminescence observed for these devices employing different cathodes differs over four orders of magnitude. Our results suggest that the electron mobility is much smaller than the hole mobility and that the recombination process is confined to a thin layer near the cathode. Additionally, the results obtained from simple device modeling are also presented.
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G. Garcia-Belmonte, E. M. Barea, Y. Ayyad-Limonge, J. M. Montero, H. J. Bolink, and J. Bisquert "Cathode effect on current-voltage characteristics of blue light-emitting diodes based on a polyspirofluorene", Proc. SPIE 6999, Organic Optoelectronics and Photonics III, 69992U (16 April 2008); https://doi.org/10.1117/12.780499
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