Organic light-emitting transistors containing a laterally arranged heterojunction

An approach to produce organic light-emitting transistors (OLETs) containing a laterally arranged heterojunction structure, which minimizes exciton quenching at the metal electrodes, is described. This device configuration provides an organic light-emitting diode (OLED) structure where the anode (source) electrode, hole-transport material (field-effect material), light-emitting material, and cathode (drain) electrode are laterally arranged, thus offering a chance to control the electroluminescent intensity by changing the gate bias. Pentacene and tris(8-quinolinolato)aluminum (Alq₃) are employed as the field-effect and light-emitting materials, respectively. The laterally arranged heterojunction structures are achieved by successively inclined deposition of the field-effect and light-emitting materials. After deposition of pentacene, a narrow gap of about 10-20 nm between the drain electrode and pentacene was obtained, thereby creating an opportunity to fabricate a laterally arranged heterojunction. In the OLETs, unsymmetrical source and drain electrodes, that is, Au and LiF/Al ones, are used to ensure efficient injection of holes and electrons. Visible-light emission from OLETs is observed under ambient atmosphere. This result is ascribed to efficient carrier injection and transport, formation of a heterojunction, as well as good luminescence from the organic emissive layer. The device structure serves as an excellent model system for OLETs and demonstrates a general concept of adjusting the charge-carrier injection and transport, as well as the electroluminescent properties, by forming laterally arranged heterojunctions.