Structural, Electronic, and Optical Properties of Pb-Free Perovskites: Dimensional Evolution from Bulk to 2D Architectures

Giacomo Giorgi^a^,^b^,^c^,^e, Maurizia Palummo^d^,^e, Koichi Yamashita^f

^aDepartment of Civil & Environmental Engineering (DICA), Via G. Duranti 93, I-06125 Perugia, The University of Perugia, Italy

^bIstituto di Scienze e Tecnologie Chimiche "Giulio Natta" (SCITEC), Consiglio Nazionale delle Ricerche - via Elce di Sotto 8, 06123 Perugia, Italy

^cCIRIAF – Interuniversity Research Centre, University of Perugia, Perugia, Italy

^dDipartimento di Fisica and INFN, Università di Roma ‟Tor Vergata”, Via della Ricerca Scientifica 1, 00133 Roma, Italy.

^eCNR-Institute of Nanoscience-S3, via G. Campi 213/a, 41125 Modena, Italy

^fGraduate School of Nanobioscience, Yokohama City University, Yokohama 236-0027, Japan

Proceedings of Asia-Pacific International Conference on Perovskite, Organic Photovoltaics and Optoelectronics (IPEROP26)

Nagoya, Japan, 2026 January 13th - 15th

Organizers: Pablo P. Boix and Seigo Ito

Oral, Giacomo Giorgi, presentation 030
Publication date: 5th November 2025

In recent years, three-dimensional lead-free halide perovskites (HPs) have attracted increasing attention, largely due to advances in stabilizing these compounds against oxidation. The substitution of lead—an element with well-known toxicity—via both homovalent (Sn, Ge) [1,2] and heterovalent (+1/+3 metal pair) strategies, [3] along with the reduction of dimensionality from 3D to mixed 3D/2D and fully 2D frameworks, has yielded materials with promising photovoltaic performance. Notably, the enhanced hydrophobic nature of low-dimensional HPs has enabled power conversion efficiencies (PCEs) approaching record values, [4] while also addressing the environmental and stability limitations of archetypal Pb-based bulk HPs.
Building on recent experimental insights, this work first examines from first-principles pristine Pb-based 2D and mixed 2D/3D HPs, emphasizing their distinct electronic and optical features and providing a comparative analysis with their Pb-free counterparts. [5] Special attention is paid to the critical influence of excitonic effects in quantum-confined systems and the fundamental relationship between symmetry and exciton behavior. [6]
Focusing on lead-free variants, the study also explores the protective function of native oxide layers developing on mixed (Sn, Ge)-based 3D HPs.[7] Remarkably, a dual nature is identified depending on whether the surface oxide adopts a crystalline or amorphous structure.

References:

[1] Ito, N. et al., Mixed Sn–Ge Perovskite for Enhanced Perovskite Solar Cell Performance in Air, J. Phys. Chem. Lett. 2018, 9, 1682–1688.

[2] Kama, A.; Tirosh, S.; Itzhak, A.; Ejgenberg, M.; Cahen, D. New Pb-Free Stable Sn–Ge Solid Solution Halide Perovskites Fabricated by Spray Deposition. ACS Appl. Energy Mater. 2022, 5, 3638–3646

[3] Palummo, M.; Berrios, E.; Varsano, D.; Giorgi, G. Optical properties of lead-free double perovskites by ab initio excited-state methods. ACS Energy Lett., 2020, 5, 457-463

[4] Zhang, Y.; Park, N.-G. Quasi-Two-Dimensional Perovskite Solar Cells with Efficiency Exceeding 22%. ACS Energy Lett. 2022, 7, 757–765

[5] Folpini, G., et al., Plurality of excitons in Ruddlesden–Popper metal halides and the role of the B-site metal cation. Mater. Adv., 2023, 4, 1720-1730.

[6] Quarti, C.; Giorgi, G.; Katan, C.; Even, J.; Palummo, M. Exciton Ground State Fine Structure and Excited States Landscape in Layered Halide Perovskites from Combined BSE Simulations and Symmetry Analysis. Adv. Opt. Mater., 2024, 12, 2202801

[7] Chen, M. et al., Highly stable and efficient all-inorganic lead-free perovskite solar cells with native-oxide passivation. Nature Commun., 2019, 10 16.

Acknowledgements:

Authors acknowledge the Hanami (Hpc AlliaNce for Applications and supercoMputing Innovation: the Europe-Japan collaboration) project via the European High Performance Computing Joint Undertaking (EuroHPC JU) under the European Union’s Horizon Europe framework program for research and innovation and Grant Agreement No. 101136269. The views and opinions expressed are those of the author(s) only and do not necessarily reflect those of the European Union or EuroHPC Joint Underting. Neither the European Union nor the granting authority can be held responsible. K.Y. acknowledges the support by MEXT as “Program for Promoting Research on the Supercomputer Fugaku” (Realization of innovative light energy conversion materials utilizing the supercomputer Fugaku, Grant No. JPMXP1020210317). G.G. acknowledges financial support under the National Recovery and Resilience Plan (NRRP), Mission 4, Component 2, Investment 1.1, Call for tender No. 104 published on 2.2.2022 by the Italian Ministry of University and Research (MUR), funded by the European Union-NextGenerationEU-Project Title 2022LZWKAJ_002 Engineered nano-heterostructures for a new generation of titania photocatalytic films (ENTI)-CUP J53D23003470006-Grant Assignment Decree No. 966 adopted on 30.06.2023 by the Italian Ministry of University and Research (MUR).

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