Spectroscopic Ellipsometry Characterization and Radiative Limit Modeling of Bismuth-Based Perovskite-Inspired Absorbers for Indoor Photovoltaics - UTU Research Portal

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Spectroscopic Ellipsometry Characterization and Radiative Limit Modeling of Bismuth-Based Perovskite-Inspired Absorbers for Indoor Photovoltaics

Authors: Kamppinen, Aleksi; Grandhi, G. Krishnamurthy; Hadadian, Mahboubeh; Toikkonen, Sami; Yli-paavola, Sirius; Vivo, Paola; Miettunen, Kati

Publication year: 2026

Journal: Advanced Optical Materials

Article number: e03237

Volume: 14

Issue: 5

eISSN: 2195-1071

DOI: https://doi.org/10.1002/adom.202503237

Publication's open availability at the time of reporting: Open Access

Publication channel's open availability : Partially Open Access publication channel

Web address : https://doi.org/10.1002/adom.202503237

Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/509019518

Self-archived copy's licence: CC BY

Self-archived copy's version: Publisher`s PDF

Abstract

Lead-free bismuth-based perovskite-inspired materials (Bi-PIMs) are emerging as wide bandgap semiconductors for sustainable optoelectronic applications, including indoor photovoltaics (IPVs). Computational modeling is a powerful tool to understand and optimize their device performance. However, device-relevant thin film optical constants for these absorbers remain scarce, limiting quantitative optical and electrical design. Here, for the first time the optical constants of two promising thin-film Bi-PIMs—Cu₂AgBiI₆ and Cs₃Bi₂I₆Br₃— are determined using spectroscopic ellipsometry. The applied graded effective medium approximation model is supported by the atomic force microscopy and scanning electron microscopy characterizations of varying film thicknesses. A realistic planar device stack is then simulated under both AM1.5G solar and 1000 lx indoor spectra. Under indoor conditions (1000 lx, 4000 K color temperature), the optical photocurrent limits are ca. 91 µA cm⁻² for Cu₂AgBiI₆ and ca. 32 µA cm⁻² for Cs₃Bi₂I₆Br₃ with the corresponding radiative-limit efficiencies of ca. 42 % and ca. 18 %, respectively. These results reveal a significant optical margin and motivate efforts to suppress nonradiative recombination and improve charge transport. More broadly, the extracted optical constants enable accurate photogeneration estimation for optoelectronic device modeling, providing insights into current performance limitations of Bi-PIM devices and guiding strategies to overcome them.

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Funding information in the publication:
A.K. thanks the University of Turku Graduate School (UTUGS), Jenny and Antti Wihuri Foundation and Lieto Savings Bank Foundation (KesPV project) for funding his doctoral research. M.H. thanks SUSMAT profiling funding (Research Council of Finland and University of Turku). G.K.G., S.T., and P.V. thank the SPOT-IT project founded by the CET Partnership, the Clean and Energy Transition Partnership under the 2022 CET Partnership joint call for research proposal, cofounded by the European Commission (GA 101069750) and with the founding of the organizations detailed on https://cetpartnership.eu/funding-agencies-and-call-modules. S.Y. and K.M. thank Circular Materials Bioeconomy Network funded by Ministry of Education and Culture, Finland (CIMANET, Decision No. VN/3137/2024-OKM-6). P.V. acknowledged funding from Research Council of Finland, Decision No. 347772. The work was part of the Research Council of Finland Flagship Programme, Photonics Research and Innovation (PREIN), Decision No. 346511.