Ultralow Dark Current Density of Organic Photodetectors and Organic Light-Emitting Diodes Endowed by Highly Thermally Stable Derivatives of 2,7-Di-tert-butyl-9,9-dimethyl-9,10-dihydroacridine and Phenanthroimidazole Exhibiting Balanced Bipolar Charge Transport

Abstract

Seeking to develop more advanced organic photodetectors (OPDs) and organic light-emitting diodes (OLEDs), we designed three derivatives of 2,7-di-tert-butyl-9,9-dimethyl-9,10-dihydroacridine and phenanthroimidazole with either −CF₃ or −C(CH₃)₃ groups. These compounds were synthesized by Buchwald–Hartwig amination reaction with yields of up to 77%. They show high glass transition temperatures above 200 °C and balanced electron and hole transport with mobilities of up to 10^–3 cm²/V·s under strong electric fields. One compound with −C(CH₃)₃ groups outperformed the standard host material in the OLED, which showed 17% higher external quantum efficiency. The low dark current density resulted in enhanced efficiency of OLEDs due to minimal charge leakage. Compared to the commercial material 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), this compound allowed achieving superior photosensitivity in OPDs. The photocurrent to dark current density ratio at a reverse voltage of −10 V was found to be 6000. For TAPC-based OPDs, this ratio was only 43.3. The dark current density was significantly reduced to 4.5 × 10^–7 mA·cm^–2, compared to 3 × 10^–4 mA·cm^–2 for TAPC-based OPDs at the same reverse voltage, thus enhancing the photosensitivity of the OPDs.