Optimizing carrier balance in CsPbBr3 nanocrystal LEDs: The role of alkyl ligands and polar electron transport layers
Roshini Jayabalan a, Girish Kakkepalaya Hanumantharaju a, Theresa Hettiger b, Arup Sarkar c, Fengshuo Zu d, Aladin Ullrich a, Norbert Koch d e, Denis Andrienko c, Marcus Scheele b, Wolfgang Brütting a
a Institute of Physics, Universität Augsburg, 86135 Augsburg, Germany
b Institute for Physical und Theoretical Chemistry, Universität Tübingen, 72076 Tübingen, Germany
c Max Planck Institute for Polymer Research, 55128 Mainz, Germany
d Helmholtz-Zentrum Berlin for Materials und Energy GmbH, 12489 Berlin, Germany
e Institute of Physics & Center for the Science of Materials Berlin, Humboldt-Universität zu Berlin, 12489 Berlin, Germany
Proceedings of Perovskite Semiconductors: From Fundamental Properties to Devices (PerFunPro)
Konstanz, Germany, 2025 September 8th - 10th
Organizers: Lukas Schmidt-Mende, Vladimir Dyakonov and Selina Olthof
Oral, Roshini Jayabalan, presentation 004
Publication date: 16th July 2025

The study of lead halide perovskite nanocrystal based light-emitting diodes (LEDs) has advanced significantly, with notable improvements in stability and optical properties. However, optimizing charge carrier injection and transport remains a challenge. Efficient electroluminescence requires a balanced transport of both holes and electrons within the emitting material. Here, we investigate cubic CsPbBr3 nanocrystals passivated with oleylamine and oleic acid, comparing them to ligand-exchanged nanocrystals with didodecyldimethylammonium bromide (DDABr). Nuclear magnetic resonance spectroscopy and transmission electron microscopy confirm successful ligand exchange, revealing reduced ligand coverage in DDABr-treated nanocrystals. Photoelectron spectroscopy, spectroelectrochemistry, and single-carrier devices indicate improved hole injection in DDABr capped nanocrystals. Density functional theory calculations further reveal the influence of ligand type and coverage on energy levels, with oleic acid introducing localized states in native nanocrystals. Additionally, incorporation of a polar electron transport layer (ETL) enhances LED performance by over an order of magnitude in DDABr-capped nanocrystals, driven by improved charge balance arising from the spontaneous orientation polarization (SOP) of the ETL. These findings highlight the critical role of ligand selection, passivation degree, and charge transport control by the adjacent organic transport layers in optimizing LED efficiency.

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