Organic Light‐Emitting Diodes Combining Thick Inorganic Perovskite Hole Transport Layers and Ultrathin Emitting Layers

Organic light‐emitting diodes have a huge gain in popularity over the past 25 years for display and lighting applications, but the production of low‐cost efficient devices remains a challenge. OLEDs using sub‐nanometer undoped emissive layers are a route to fabricate cost‐effective devices but, as they are inherently thin, it opens to issues with variation in thickness and shunting paths. At the same time, lead chloride perovskites are currently being investigated as charge transport materials in light‐emitting devices owing to their wide bandgap, and remarkable high carrier mobility. In this work, for the first time, OLEDs that combine vacuum‐processed thick cesium lead chloride perovskite hole transport layers with ultrathin Ir complex‐based emissive layers are reported. Defects on the perovskite film are suppressed and the thickness of the emitting layer is optimized. Semitransparent devices are also fabricated with an average visible transmittance of over 50%. The results show extraordinarily thick devices (>1 µm) with low turn‐on voltage (3.3 V), high luminance (>15 000 cd m −2 ) and efficiencies (up to 54.1 cd A −1 ), and a negligible efficiency roll‐off in the display applications luminance region.