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. 2025 Apr 11;10(5):2268-2276.
doi: 10.1021/acsenergylett.5c00124. eCollection 2025 May 9.

Improving the Stability of Colloidal CsPbBr3 Nanocrystals with an Alkylphosphonium Bromide as Surface Ligand Pair

Meenakshi Pegu  1 , Hossein Roshan  1 , Clara Otero-Martínez  1 , Luca Goldoni  1 , Juliette Zito  1 , Nikolaos Livakas  1   2 , Pascal Rusch  1 , Francesco De Boni  1 , Francesco Di Stasio  1 , Ivan Infante  3   4 , Luca De Trizio  1 , Liberato Manna  1
Affiliations

Improving the Stability of Colloidal CsPbBr3 Nanocrystals with an Alkylphosphonium Bromide as Surface Ligand Pair

Meenakshi Pegu et al. ACS Energy Lett. .

Abstract

In this study, we synthesized a phosphonium-based ligand, trimethyl(tetradecyl)phosphonium bromide (TTP-Br), and employed it in the postsynthesis surface treatment of Cs-oleate-capped CsPbBr3 nanocrystals (NCs). The photoluminescence quantum yield (PLQY) of the NCs increased from ∼60% to more than 90% as a consequence of replacing Cs-oleate with TTP-Br ligand pairs. Density functional theory calculations revealed that TTP+ ions bind to the NC surface by occupying Cs+ surface sites and orienting one of their P-CH3 bonds perpendicular to the surface, akin to quaternary ammonium passivation. Importantly, TTP-Br-capped NCs exhibited higher stability in air compared to didodecyldimethylammonium bromide-capped CsPbBr3 NCs (which are considered a benchmark system), retaining ∼90% of their PLQY after 6 weeks of air exposure. Light-emitting diodes fabricated with TTP-Br-capped NCs achieved a maximum external quantum efficiency of 17.2%, demonstrating the potential of phosphonium-based molecules as surface ligands for CsPbBr3 NCs in optoelectronic applications.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Scheme 1
Scheme 1. Sketch of the Post-Synthesis Ligand Exchange Process Involving Treatment of Cs-Oleate-Capped CsPbBr3 NCs with TTP-Br
Figure 1
Figure 1
(a) TEM micrograph of TTP-Br-capped CsPbBr3 NCs. (b) X-ray diffraction pattern of TTP-Br-capped CsPbBr3 NCs and reference CsPbBr3 orthorhombic bulk reflections (ICSD Number 243735). (c) XPS P2p spectra of TTP-Br- and Cs-Oleate-capped CsPbBr3 NCs. (d) FTIR spectra of the TTP-Br ligand and TTP-Br- and Cs-oleate-capped CsPbBr3 NCs. (e) 1H NMR spectra at 298 K of Cs-oleate- and TTP-Br-capped CsPbBr3 NCs (see the Supporting Information for more details). (f) 2D NOESY spectrum of TTP-Br-capped CsPbBr3 NCs at 313 K (see Supporting Information for the detailed spectrum).
Figure 2
Figure 2
(a) UV–visible absorption and PL spectra of Cs-oleate-, DDA-Br-, and TTP-Br-capped CsPbBr3 NCs. (b) PL decay profile of Cs-oleate-, DDA-Br-, and TTP-Br-capped CsPbBr3 NCs. (c) Binding configuration of TTP-Br- ligands sitting in the A-site of the CsPbBr3 NCs’ surface. (d) PLQY stability of Cs-oleate-, DDA-Br-, and TTP-Br-capped CsPbBr3 NCs over time at ambient storage conditions.
Figure 3
Figure 3
(a) Double HTL LED device configuration based on TTP-Br-capped CsPbBr3 NCs. (b) Band-energy alignment of TTP-Br-capped CsPbBr3 NCs with charge injection layers. (c) PL spectrum of TTP-Br-capped CsPbBr3 NC film and EL spectra of the double HTL LED at different applied voltages. (d) Current density and luminance versus driving voltage curves of the double HTL TTP-Br-capped CsPbBr3 NC-based champion LED device. (e) EQE versus current density of the double HTL LEDs champion devices based on TTP-Br-capped and DDA-Br-capped CsPbBr3 NCs. (f) Stability of the EL intensity under operation conditions with the initial luminance of 500 cd/m2, while the inset shows the intensity of light plotted over time with an applied bias of 7 V.
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