Electron Affinity Control of Amorphous Oxide Semiconductors and Its Applicability to Organic Electronics

Abstract

Energy level matching is a key factor for realizing efficient optoelectronics, such as organic light-emitting diodes (OLEDs). Transition metal oxides (TMOs) are widely used as hole-injection layers (HILs) because of their large electron affinities, corresponding to conduction band minimum levels (E-CBM). However, the poor electrical properties and chemical instabilities of TMOs restrict device performance and fabrication processes. Conversely, amorphous oxide semiconductors (AOSs) exhibit superior electrical properties and chemical stability but cannot be applied to HILs because of their small electron affinities. In this study, a novel method is proposed to tune the electron affinity of conventional AOSs and an example material design of AOSs for HILs. The electron affinity deepening phenomenon that is attributable to the higher oxidation states of transition metal cations achieves a very deep E-CBM of 5.7 eV for the proposed amorphous In-Mo-O (a-IMO). Furthermore, an a-IMO exhibits a high mobility of approximate to 1 cm(2) V-1 s(-1) and high chemical stability against various solvents. As a result, it is demonstrated that a very thick a-IMO layer is applicable to OLEDs as an HIL with no operating-voltage increase. This study provides a new approach for efficient organic optoelectronics by tuning the electron affinity of AOSs.