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Organic single crystals are highly promising for applications in optoelectronic devices because of their higher mobility and thermal stability than amorphous thin films. Although white organic single crystals have been fabricated by the double-doped method and applied to realize white organic light‐emitting devices (WOLEDs), the unbalanced carrier transport properties of the unipolar crystals severely limit the device performance. Here, ambipolar white organic single crystals are obtained by using mixed p- and n-type molecules as an ambipolar host for the red and green dopants. The white crystal with balanced carrier transport and balanced blue, green, and red emission intensity was applied to the single-crystal WOLEDs. The highest brightness of 1956 cd m−2 and the current efficiency of 1.31 cd A−1 are achieved, which are the best performance of the single-crystal WOLEDs reported to date. A high color rendering index is obtained, which varies between 82 and 87 with increasing driving current. It is expectable that this strategy would support the practical applications of organic single crystal-based OLEDs. [ABSTRACT FROM AUTHOR]

Carrier mobility is one of the key issues for applications of organic semiconductors in electronic and optoelectronic devices. Organic single crystals possess much higher carrier mobility compared to amorphous films. However, unipolar properties with unbalanced hole and electron transporting ability have been a bottleneck for the high performance of organic single crystal‐based devices. Here, well‐balanced ambipolar organic single crystals are developed by mixing of n‐ and p‐type molecules with maintained single‐crystalline structures. Carrier mobility of the ambipolar single crystals is manipulated by tuning the mixing ratio, and nearly equal hole and electron mobility can be achieved. Highly efficient single crystal‐based organic light‐emitting devices (OLEDs) are demonstrated by employing the ambipolar crystals as the mixed host for a red emitter pentacene to realize efficient exciton confinement and energy transfer within the emissive layer. As a result, maximum luminance of 5467 cd m−2 and current efficiency of 2.82 cd A−1 are achieved, which represents, to the best of the authors' knowledge, the record performance for the organic single crystal‐based OLEDs to date. The strategy to manipulate the charge‐transport properties of the organic single crystals in this work represents a significant step toward practical applications of the organic single crystals in optoelectronics. [ABSTRACT FROM AUTHOR]