(276d) Doped Perovskite Nanocrystals for Efficient Blue Light Emitting Diodes

Interest in perovskite (ABX₃) LEDs has exploded over the past several years due to their strong light-emitting properties, tunable emission, and facile fabrication. High performance red and green devices have been demonstrated by several groups, with external quantum efficiencies (EQEs) over 20%, matching OLED performance. Blue LEDs, however, have lagging significantly behind. Here, we identify and rectify two crucial issues holding perovskite nanocrystals back: their low internal photoluminescence yield and the LED device structure itself.

First, we show that NiOx, a common hole transport layer in these materials, induces defects in the nanocrystals, reducing emission by an order of magnitude and introducing rapid decay channels. To fix this issue, we design a new hole transport layer based on a combination of a traditional hole transport layer and perfluorinated ionomer, allowing the nanocrystals to emit with their native efficiency and lifetime. We then show that this translates directly to devices, increasing the EQE from 0.03% to 0.50%. Further, we show that the benefits apply to devices across the visible spectrum, with efficient blue, sky-blue, and green devices.

Next, we demonstrate that a large portion of the lost efficiency is due to inherent emission losses in the blue perovskite nanocrystals, as they demonstrate a thin film photoluminescence quantum yield of less that 10%. This can be rectified, however, by taking advantage of a surprising effect. When doping the nanocrystals with Mn, which introduces an energetic loss pathway to an orange emissive state, we counterintuitively observe an increase in perovskite emission. By carefully tuning the amount of Mn in the nanocrystal, we can increase the quantum yield over 3x. This translates directly to device performance, as doped devices reach a maximum EQE of 2.1%. The combination of the device and dopant improvements increases performance by over 60x, showing that blue perovskite materials can be competitive with their red and green cousins. Finally, we use this efficient blue emitter to build an all-perovskite white LED, which has important applications in lighting.

We will conclude the talk by demonstrating that Mn is not alone as an effective dopant: several other atomic dopants across the periodic table provide similar benefit. We will present the similarities and differences amongst these dopant conditions and show how we can use them to push device performance even further.