Turning instability into functionality: Stoichiometry-and moisture-tuned reversible multichromism in Ethylammonium perovskites

Turning instability into functionality: Stoichiometry-and moisture-tuned reversible multichromism in Ethylammonium perovskites | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Turning instability into functionality: Stoichiometry-and moisture-tuned reversible multichromism in Ethylammonium perovskites Soohyung Park, Aelim Ha, Seunghwan Kim, Kitae Kim, Eunki Yoon, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9305944/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Organic–inorganic hybrid perovskites located at the boundaries of the Goldschmidt tolerance factor exhibit a structural softness that affords unique stimuli responsiveness but complicates their intrinsic phase stability. Ethylammonium (EA)-based perovskites, in particular, have long suffered from ambiguous and conflicting crystallographic reports, with their responses to moisture environments often misinterpreted as irreversible chemical degradation. Here, we resolve this long-standing structural ambiguity by identifying environmental humidity as a hidden variable whose impact is critically gated by precursor stoichiometry. We demonstrate that reaching a specific compositional threshold ([EAI]/[PbI 2 ] ≥ 1.6) transforms the otherwise structurally rigid or degradation-prone perovskite lattice into a highly flexible mixed-dimensional landscape. Within this responsive regime, moisture triggers a rapid, synchronized, and fully reversible reconfiguration between 1D- and 2D-related structural motifs, that we call a dynamic lattice rearrangement, without chemical decomposition (PbI 2 formation), which manifests as a repeatable multicolor hydrochromism. Practically leveraging this stoichiometry-gated dynamics, we successfully demonstrate zero-power, autonomous smart windows that adapt to external weather conditions, as well as dual-functional medical moisture indicators capable of both irreversible moisture history logging and real-time quantitative monitoring. This work establishes a new paradigm for boundary-region perovskites, turning their inherent instability into innovative functionality for active environmental sensing and smart optoelectronic devices. Physical sciences/Materials science Physical sciences/Physics/Applied physics Physical sciences/Physics/Condensed-matter physics Physical sciences/Materials science/Nanoscale materials Physical sciences/Materials science/Condensed-matter physics Full Text Additional Declarations There is NO Competing Interest. Supplementary Files Si.docx Supplementary Information Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9305944","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":616992047,"identity":"8a314c4d-241d-4b01-b692-57cc56f0843e","order_by":0,"name":"Soohyung 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Ethylammonium (EA)-based perovskites, in particular, have long suffered from ambiguous and conflicting crystallographic reports, with their responses to moisture environments often misinterpreted as irreversible chemical degradation. Here, we resolve this long-standing structural ambiguity by identifying environmental humidity as a hidden variable whose impact is critically gated by precursor stoichiometry. We demonstrate that reaching a specific compositional threshold ([EAI]/[PbI\u003csub\u003e2\u003c/sub\u003e] ≥ 1.6) transforms the otherwise structurally rigid or degradation-prone perovskite lattice into a highly flexible mixed-dimensional landscape. 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