Charge-carrier injection assisted by space-charge field in AC-driven organic light-emitting transistors

Organic light-emitting transistors can be operated by an alternating gate voltage to provide high light output intensity. We propose a model for the light generation process in such light-emitting transistors based on systematic measurements of how the light output intensity depends on the biasing parameters. Following injection of holes, which form a positively charged space-charge region, subsequent electron tunneling from the same metal electrode eventually leads to light emission from the organic emitter. The electron injection is found to depend on the positive space-charge region, and the hole injection efficiency therefore strongly influences the emission intensity. Low temperature measurements show increased emission intensity as the temperature decreases indicating that the light generation is dependent on thermally activated charge injection, i.e., Fowler-Nordheim tunneling theory is not applicable. Further metal/semiconductor interface modification could result in optimized charge injection under AC biasing, thus leading to more efficient organic light-emitting devices. (C) 2011 Elsevier B.V. All rights reserved.