Organic Light-Emitting Diodes Comprising an Undoped Thermally Activated Delayed Fluorescence Emissive Layer and a Thick Inorganic Perovskite Hole Transport Layer

Abstract

Organic light-emitting diodes (OLEDs) hold potential for next-generation displays and lighting solutions, but current OLED displays rely on the use of scarce metals or fluorescent emitters. Thermally activated delayed fluorescence (TADF) compounds kickstarted a new, promising class of OLEDs as organic TADF emitters do not contain scarce platinoid elements yet remain highly efficient. However, similarly to phosphorescent emitters, their incorporation into devices typically requires complicated doping techniques when vacuum processed. Lowering the mass production costs of high-performing OLEDs using simpler fabrication techniques remains a challenge. Here, we report OLEDs comprising a thermally evaporated CsPbCl₃ perovskite transport layer and a TADF-based single-component emitting layer by exploring different approaches to obtain efficient undoped OLEDs, both solution- and vacuum-processed. We first demonstrated the compatibility of the perovskite layer with the solution processing of a TADF dendrimer for host-free, thick emitting layers, with an efficiency of 15 cd A^–1 well over a luminance of 1000 cd m^–2. Then, we employed a TADF small molecule as the emitter and reduced its layer’s thickness to the subnanometer regime, while the incorporation of the perovskite increased the required total device thickness. The resulting devices showed a low turn-on voltage of 3.3 V, a high luminance of 11 152 cd m^–2, and a high efficiency of 67.6 cd A^–1, equaling that of 20 times thicker emissive layers. These findings highlight the versatility of using a perovskite as a transport layer and the potential of combining it with an undoped TADF emitting layer for fabricating simple, cost-effective, and efficient OLEDs.