Divergent Solid-state Conversion Pathways in Evaporated All-perovskite Tandem Solar Cells
Abstract
Sequential thermal evaporation (sTE) is emerging as a solvent-free route to high-quality mid-bandgap perovskites, but its extension to mixed-halide wide-bandgap (WBG) and Sn-Pb narrow-bandgap (NBG) absorbers for all-perovskite tandem solar cells (TSCs) remains limited by an incomplete understanding of solid-state conversion. Here, using time-sliced ex situ analysis, we reveal divergent solid-state conversion mechanisms in sequentially evaporated WBG and NBG precursor stacks. In WBG stacks, formamidinium (FA)-containing species penetrate the inorganic template and Br/I redistribution precedes substantial three-dimensional perovskite formation. The photoactive phase then crystallizes from a chemically mixed reservoir, and absolute PbBr2 thickness, rather than nominal PbBr2/PbI2 ratio, determines the final bandgap. In NBG stacks, by contrast, an early Pb-rich perovskite phase forms upon formamidinium iodide deposition, restricting further FA penetration into the buried SnI2 precursor. Subsequent annealing promotes rapid lattice reorganization faster than Sn/Pb interdiffusion, leaving vertical compositional gradients. Guided by these insights, we develop sTE absorbers with bandgaps spanning 1.26-1.96 eV and demonstrate the first evaporated all-perovskite TSC, reaching a power conversion efficiency of 19.2%. Encapsulated tandems retain on average 80% of their initial efficiency after 1,200 h at 65 ∘C (ISOS-D-2). These results establish bandgap-specific control of solid-state conversion as a design principle for sequentially evaporated perovskite tandem photovoltaics.
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BibTeX
@misc{lai2026divergent,
title = {{Divergent Solid-state Conversion Pathways in Evaporated All-perovskite Tandem Solar Cells}},
author = {Huagui Lai and Amber Wright and Nick Huber and Niels Uythoven and Federico De Giorgi and Jincheng Luo and Tristan Sachsenweger and Sunil B. Shivarudraiah and Chih-Jen Shih and Wolfgang Tress and Fan Fu},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.20326},
eprint = {2609.20326},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.20326},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Divergent Solid-state Conversion Pathways in Evaporated All-perovskite Tandem Solar Cells
AU - Huagui Lai
AU - Amber Wright
AU - Nick Huber
AU - Niels Uythoven
AU - Federico De Giorgi
AU - Jincheng Luo
AU - Tristan Sachsenweger
AU - Sunil B. Shivarudraiah
AU - Chih-Jen Shih
AU - Wolfgang Tress
AU - Fan Fu
PY - 2026
DA - 2026/09/17
PB - arXiv
DO - 10.48550/arxiv.2609.20326
UR - https://arxiv.org/abs/2609.20326
AB - Sequential thermal evaporation (sTE) is emerging as a solvent-free route to high-quality mid-bandgap perovskites, but its extension to mixed-halide wide-bandgap (WBG) and Sn-Pb narrow-bandgap (NBG) absorbers for all-perovskite tandem solar cells (TSCs) remains limited by an incomplete understanding of solid-state conversion. Here, using time-sliced ex situ analysis, we reveal divergent solid-state conversion mechanisms in sequentially evaporated WBG and NBG precursor stacks. In WBG stacks, formamidinium (FA)-containing species penetrate the inorganic template and Br/I redistribution precedes substantial three-dimensional perovskite formation. The photoactive phase then crystallizes from a chemically mixed reservoir, and absolute PbBr_2 thickness, rather than nominal PbBr_2/PbI_2 ratio, determines the final bandgap. In NBG stacks, by contrast, an early Pb-rich perovskite phase forms upon formamidinium iodide deposition, restricting further FA penetration into the buried SnI_2 precursor. Subsequent annealing promotes rapid lattice reorganization faster than Sn/Pb interdiffusion, leaving vertical compositional gradients. Guided by these insights, we develop sTE absorbers with bandgaps spanning 1.26-1.96 eV and demonstrate the first evaporated all-perovskite TSC, reaching a power conversion efficiency of 19.2%. Encapsulated tandems retain on average 80% of their initial efficiency after 1,200 h at 65 ^∘C (ISOS-D-2). These results establish bandgap-specific control of solid-state conversion as a design principle for sequentially evaporated perovskite tandem photovoltaics.
ER -