Tuning optical properties and local lone-pair off-centering in “hollow” FA1-x{en}xPbh-ySnyBr3 perovskites

Sep 30, 2026

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Hollow metal halide perovskites extend tunability within limited compositional spaces, enabling control of optical properties and local structure via lone-pair induced off-centering. The study focuses on mixed-metal FA1−xenxPbh−ySnyBr3 hollow perovskites with optical gaps from 1.9 eV to 2.6 eV, combining Pb/Sn bandgap red-shifting and blue-shifting from organic substitution. Single-crystal X-ray diffraction and total X-ray scattering pair distribution function analyses reveal incoherent off-centering distortions locally correlated with Sn concentration. Ethylenediammonium dications regulate metal off-centering, opening research opportunities.

LanguageEnglish

CategoryResearch & Report

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Pages18

Reading Time45 min

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Introduction

Metal halide perovskites as optoelectronic semiconductors

Limits from constrained compositional space

Limits from ambient stability and degradation

Motivation for “hollow” metal halide perovskites (hMHP)

Chemical Science EDGE ARTICLE Cite this: DOI: 10 .1039/d5sc01841b All publication charges for this article have been paid for by the Royal Society of Chemistry Received 7th March 2025 Accepted 20th October 2025 DOI: 10.1039/d5sc01841b [rsc.li/chemical-science](rsc.li/chemical-science) Tuning optical properties and local lone-pair oﬀcentering in “hollow” FA1 −x{en}xPbh −ySny Br3 perovskites Adam Balvanz, a Anastasia Pournara,a Robert P. Reynolds, a Patricia E. Meza, b Christos D. Malliakas, a Jared D. Fletcher,a Ram Seshadri, c Vinayak P. Dravid band Mercouri G. Kanatzidis *ad Hollow metal halide perovskites, while a relatively recent discovery, have already been shown to push the boundaries of tuneability within an inherently limited compositional space. Here, we further expand our knowledge of these complex materials demonstrating the ability to control optical properties and local structure, notably lone-pair induced oﬀ-centering. We focus on the mixed metal FA1 −xenxPbh −ySnyBr3 hollow perovskites. These compounds have wide ranging optical gaps from 1 . 9 eV (deep red) to 2 . 6 eV (light yellow), combining the anomalous bandgap red-shifting of Pb/Sn mixing with the blue-shifting eﬀects of the organic substitution. Average and local structural studies employing single crystal X-ray diﬀraction and total X-ray scattering pair distribution function analyses respectively suggest strong incoherent oﬀ-centering distortions that are locally correlated with Sn concentration. The inclusion of ethylenediammonium dications appears to regulate metal oﬀ-centering, opening new opportunities of research into this phenomenon. 1 Introduction Metal halide perovskites (MHPs) are a promising class of optoelectronic materials with wide-ranging applications in devices that employ high-performance semiconductors: photovoltaics (including single1–5 and multijunction6–11 devices), radiation detectors,12–16 and light-emitting diodes (LEDs)17–20 to name a few. These compounds are highly absorbing, direct-gap semiconductors with high charge carrier mobilities21 that can be easily synthesized through low-cost synthetic methods and starting materials.22 Unlike conventional semiconductors such as silicon and gallium arsenide, MHPs display a remarkable resiliency to electronic defect states, making them a focal point for scienti􀀁c research eﬀorts and technological advancements as a cost-eﬀective alternative.23–25 In addition, compositions can be engineered to match a desired optical band gap (Eg), with few exceptions, through simple chemical substitutions, accessing semiconductors with Eg ∼1.2–2.4 eV.26–29 With regard to photovoltaic applications, despite their rapid accent in power aNorthwestern University Department of Chemistry, Evanston, IL 60208, USA. E-mail: [m-kanatzidis@northwestern.edu](m-kanatzidis@northwestern.edu) bNorthwestern University Department of Materials Science and Engineering, Evanston IL, 20208, USA cMaterials Department and Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA dMaterials Science Division, Argonne National Laboratory, Lemont, IL 60439, USA conversion eﬃciency, MHPs fundamentally suﬀer from two endemic pitfalls to their commercial viability. A limiting feature of the MHP family, speci􀀁cally the highestperforming three-dimensional (3D) variety, is the constrained compositional space. De􀀁ned as an AMX3 composition (where A and M are mono and divalent cations respectively and X is a monovalent anion) there are only three A-site cations (formamidinium (FA+), methylammonium (MA+), and Cs+) and limited M-site cations (Ge2+, Sn2+, Pb2+) and three X-site anions (Cl − , Br − , I −) that can form a perovskite framework (with some exceptions).30,31 These limitations are re􀀃ective of the geometric requirements to stabilize the 3D perovskite structure.32,33 If only considering compositions with potential applications, the Msite possibilities are narrowed furthe

FAQs

What material system is investigated in the study?

The research examines mixed-metal hollow perovskites of the form FA1−xenxPbh−ySnyBr3, where ethylenediammonium regulates structural behavior and Pb/Sn mixing tunes optical responses.

How are optical properties tuned across the studied compounds?

Optical gaps range from 1.9 eV to 2.6 eV by combining anomalous bandgap red-shifting from Pb/Sn mixing with blue-shifting effects caused by organic substitution.

What evidence is used to analyze local structure and off-centering?

Average and local structural studies use single-crystal X-ray diffraction and total X-ray scattering pair distribution function analyses, which indicate strong incoherent off-centering distortions correlated with Sn concentration.

Sep 30, 2026

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