Carrier transport regulation with hole transport trilayer for efficiency enhancement in quantum dot light-emitting devices

Abstract Due to deep valence energy level of colloidal quantum dots (QDs), it's challenge to achieve efficient hole injection from organic function materials to QDs. To improve hole injection, hole transport trilayer (HTTL), consisting of 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP)/4,4′,4″-tris(carbazol-9-yl) triphenylamine (TCTA)/di-[4-(N,N-di(p-tolyl)-amino)-phenyl]cyclohexane (TAPC) is introduced into inverted quantum dot light-emitting devices (QLEDs). Due to the formation of cascade energy levels, the HTTL is expected to facilitate hole injection, decrease hole accumulation at QDs/hole transport layer (HTL) interface and reach better carrier balance. As a result, compared with control device without cascade energy levels, 64% enhancement in device performances is achieved for the optimized green QLED with cascade energy levels. It is proved that the reduced holes accumulation and improved carrier balance are the main reasons for the considerable efficiency enhancement.