Odd–Even Cation Engineering of the Excitation Transport Anisotropy in Two-Dimensional Perovskite Films

Journal article

Two-dimensional perovskites have emerged as promising materials for optoelectronic applications owing to their excellent environmental stability and tunable quantum confinement. Such 2D perovskites can incorporate a particularly versatile range of organic cations of different size, chemical nature, and optoelectronic character. However, understanding and controlling thin-film transport for this vast family of materials remains a key challenge to their successful application in devices. Here, we systematically investigate odd–even effects in thin films of Ruddlesden–Popper-type (RP) lead-iodide 2D perovskites based on nonconjugated alkylammonium spacer cations with chain lengths ranging from three to eight carbon atoms. A pronounced odd–even dependence on the carbon number is observed in both optical and transport properties, including absorption coefficients, photoluminescence energies and lifetimes, and excitation diffusion dynamics. Notably, the coefficients for charge-carrier diffusion out of the film planeextracted via a dynamic photon reabsorption approachdisplay an opposite odd–even trend to the in-plane charge-carrier mobility obtained from optical pump–terahertz probe measurements, causing a pronounced odd–even modulation of the thin-film mobility anisotropy. Grazing-incidence wide-angle X-ray scattering measurements reveal that this behavior is related to cation-controlled nanostructural orientation: even-numbered alkyl spacer cations induce lead-iodide planes lying highly oriented within the film plane, while odd-numbered ones cause more disordered stacking. Furthermore, the observed 1/d2-dependence on interplane distance d in ordered films demonstrates that Förster resonance energy transfer underpins diffusion of excitations between lead-iodide layers. Our findings establish a direct structure–transport correlation in 2D perovskite films and provide valuable guidelines for the design of optoelectronic devices.

Authors: Du, J; Righetto, M; Choghaei, M; Yan, S; Wallerius, CA

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Chemical Society
• Journal: ACS Nano
• Volume: 20
• Issue: 21
• Pages: 15706-15715
• Publication date: 2026-05-20
• Acceptance date: 2026-05-13
• DOI: 10.1021/acsnano.6c05301
• EISSN: 1936-086X
• ISSN: 1936-0851
• Language: English
• Keywords: photon reabsorption; transport; odd−even effect; 2D perovskite; anisotropy; photoluminescence