Blended layer brings hybrid light emitting transistors closer to practical applications

A light emitting transistor (LET) is an optoelectronic device that combines light emission and electrical switching. This device could simplify the design of active matrix displays, a technology used in liquid crystals.

Single layer LET lacks high current density and strong light intensity. Hybrid LETs solve this problem because they include both high mobility oxide transport layers and organic emissive layers. But for hybrid LETs to be of practical use, the difference between their optical and electrical turn-on voltages must be minimized. To address this challenge, Ablat et al. created a novel hybrid LET achieving lower optical turn-on voltage.

The inventive step is the addition of a blended emissive polymer layer incorporating a hole transport small molecule. Because the hole transport small molecule is a part of the emissive polymer layer, it acts as an immediate source of positive charges, which permits more efficient light emission when the transistor is turned on electrically.

The authors found that their blended layer significantly decreases the optical turn-on voltage from 27 volts to 2 volts, but quite remarkably the electrical turn-on voltage remains almost the same. The blended layer also enhances other optical performance measures of LETs, including brightness and external quantum efficiency. The results demonstrate that the blended layer improves the overall LET hybrid performance.

Author Mamatimin Abbas said that this work surmounts an important issue with LETs, bringing these devices closer to practical applications. However, other issues remain, which the authors plan to focus on in the future.

Source: “Low optical turn-on voltage in solution processed hybrid light emitting transistor,” by Abduleziz Ablat, Adrica Kyndiah, Alexandre Bachelet, Kazuo Takimiya, Lionel Hirsch, Sophie Fasquel, and Mamatimin Abbas, Applied Physics Letters (2019). The article can be accessed at https://doi.org/10.1063/1.5090220 .