Organic single‐crystal light‐emitting transistors with external quantum efficiency over 20

Organic light‐emitting transistors (OLETs) have attracted increasing attention because of their potential applications in next‐generation displays and high‐energy operating devices. However, the simultaneous achievement of high luminescent efficiency and carrier mobility in organic semiconductors remains challenging because the localized excitons are advantageous for light emission, whereas the delocalized carriers are beneficial for efficient charge migration. Herein, we report an organic single crystal of a cyano‐substituted styrene derivative with balanced mobility yielding a record‐high external quantum efficiency of 20.5% in OLETs. Temperature‐dependent I–V curves and electronic structure analyses based on first‐principles calculations were performed to disclose the underlying mechanism as a band transport, which provides an efficient way to achieve high quantum efficiency in OLETs. Organic light‐emitting transistors fabricated using a single‐crystal cyano‐substituted styrene derivative yield quantum efficiency over 20%. Strong intermolecular forces present within the low‐defect crystal enable low charge‐carrier activation energies and band transport properties comparable to the rubrene crystal, which is further supported by theoretical calculations.