Modified Maxwell–Wagner model analysis on charging and discharging in TIPS-pentacene diode by optical second harmonic generation measurement

We used time-resolved electric field induced optical second harmonic generation (TR-EFISHG) measurement and Maxwell–Wagner (MW) equivalent circuit model analysis to study the charging and discharging processes of ITO/Polyimide/6,13-Bis(triisopropylsilylethynyl)-pentacene/Au (ITO/PI/TIPS-pentacene/Au) diodes. For fresh diodes, electrode charging was followed successively by interfacial charging, whereas interfacial discharging occurred very quickly in combination with electrode discharging. In contrast, the order of charging and discharging was reversed for aged diodes. A modified MW equivalent circuit well accounts for these results, where TIPS-pentacene functions as a dielectric material before hole injection, but as a conductor after hole injection. As a result, the accumulated interfacial charge can escape very quickly from the TIPS-pentacene together with electrode discharging. These results illustrate the non-reversal behavior of the fresh TIPS-pentacene diodes.