Increased Brightness and Reduced Efficiency Droop in Perovskite Quantum Dot Light-Emitting Diodes Using Carbazole-Based Phosphonic Acid Interface Modifiers
Gillian Shen, Yadong Zhang, Juan F. Bada Juarez, Hannah Contreras, Collin Sindt, Yiman Xu, Jessica Kline, Stephen Barlow, Elsa Reichmanis, Seth R. Marder, David S. Ginger
Abstract
We demonstrate the use of [2-(9 H -carbazol-9-yl)ethyl]phosphonic acid (2PACz) and [2-(3,6-di- tert -butyl-9 H -carbazol-9-yl)ethyl]phosphonic acid ( t -Bu-2PACz) as anode modification layers in metal-halide perovskite quantum dot light-emitting diodes (QLEDs). Compared to conventional QLED structures with PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrenesulfonate)/PVK (poly(9-vinylcarbazole)) hole-transport layers, the QLEDs made with phosphonic acid (PA)-modified indium tin oxide (ITO) anodes show an over seven-fold increase in brightness, achieving a brightness of 373,000 cd m –2, one of the highest brightnesses reported to date for colloidal perovskite QLEDs. Importantly, the onset of efficiency roll-off, or efficiency droop, occurs at ∼1000-fold higher current density for QLEDs made with PA-modified anodes compared to control QLEDs made with conventional PEDOT:PSS/PVK hole transport layers, allowing the devices to sustain significantly higher levels of external quantum efficiency at a brightness of >10 5 cd m –2 . Steady-state and time-resolved photoluminescence measurements indicate that these improvements are due to a combination of multiple factors, including reducing quenching of photoluminescence at the PEDOT:PSS interface and reducing photoluminescence efficiency loss at high levels of current density.