Experimentally informed drift-diffusion assessment of a lead-free four-terminal BaZr0.85Ti0.15S3/CZTSSe tandem solar cell
Abstract
A lead-free four-terminal tandem architecture is assessed by optically coupling a semi-transparent BaZr0.85Ti0.15S3 chalcogenide-perovskite top sub-cell to a Cu2ZnSn(S0.25Se0.75)4 (CZTSSe) bottom sub-cell. The assessment includes a 33.93% idealized design target only as an upper bound because the assumed p-type, low-defect top absorber has not been demonstrated in a photovoltaic device. The device physics are evaluated with a one-dimensional drift-diffusion framework based on the coupled Poisson and electron/hole continuity equations. A finite-volume Python implementation using Scharfetter-Gummel fluxes was benchmarked against a fresh SCAPS 3.3.08 single-junction calculation, giving differences of 0.842 mV in open-circuit voltage, 0.049 mA cm− 2 in short-circuit current density, and 0.056% point in fill factor; the J-V root-mean-square error was 0.169 mA cm− 2. The tandem parameter set was anchored to measured BaZrS3 thin-film transport and defect ranges and to a recent high-performance CZTSSe device. Under the favorable n-type top-absorber boundary, optical/electrical co-optimization moves the BaZr0.85Ti0.15S3 thickness from 0.90 μm to 0.05 μm and gives 3.30% from the top cell plus 13.56% from the filtered bottom cell, for a 16.86% four-terminal efficiency. A 1200-sample material/contact uncertainty analysis at this thickness gives P5, median, and P95 efficiencies of 8.07%, 10.73%, and 15.49%, respectively. An additional 55-case direct SCAPS sweep over donor density, bulk defect density, minority-hole mobility, and trap capture cross section, together with maximum-power-point depth profiles, identifies defect-mediated recombination and minority-hole collection as the controlling top-cell constraints. The results show that the proposed absorber pair remains scientifically interesting, but its performance is controlled by minority-hole transport, sulfur-vacancy-related n-type doping, top-cell thickness, bottom-cell material quality, and contact resistance. Accordingly, 33.93% should be interpreted as a long-term material-quality ceiling rather than an experimentally credible near-term prediction.
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BibTeX
@article{hasnain2026experimentally,
title = {{Experimentally informed drift-diffusion assessment of a lead-free four-terminal BaZr0.85Ti0.15S3/CZTSSe tandem solar cell}},
author = {Syed M. Hasnain and M. Amin Mir and Muhammad Waqar Ashraf and Abid Iqbal and Ali S. Alzahrani and Syed Hashim Raza Bukhari},
journal = {Scientific Reports},
year = {2026},
month = oct,
doi = {10.1038/s41598-026-74658-2},
url = {https://www.nature.com/articles/s41598-026-74658-2},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - JOUR
TI - Experimentally informed drift-diffusion assessment of a lead-free four-terminal BaZr0.85Ti0.15S3/CZTSSe tandem solar cell
AU - Syed M. Hasnain
AU - M. Amin Mir
AU - Muhammad Waqar Ashraf
AU - Abid Iqbal
AU - Ali S. Alzahrani
AU - Syed Hashim Raza Bukhari
PY - 2026
DA - 2026/10/05
JO - Scientific Reports
DO - 10.1038/s41598-026-74658-2
UR - https://www.nature.com/articles/s41598-026-74658-2
AB - A lead-free four-terminal tandem architecture is assessed by optically coupling a semi-transparent BaZr0.85Ti0.15S3 chalcogenide-perovskite top sub-cell to a Cu2ZnSn(S0.25Se0.75)4 (CZTSSe) bottom sub-cell. The assessment includes a 33.93% idealized design target only as an upper bound because the assumed p-type, low-defect top absorber has not been demonstrated in a photovoltaic device. The device physics are evaluated with a one-dimensional drift-diffusion framework based on the coupled Poisson and electron/hole continuity equations. A finite-volume Python implementation using Scharfetter-Gummel fluxes was benchmarked against a fresh SCAPS 3.3.08 single-junction calculation, giving differences of 0.842 mV in open-circuit voltage, 0.049 mA cm− 2 in short-circuit current density, and 0.056% point in fill factor; the J-V root-mean-square error was 0.169 mA cm− 2. The tandem parameter set was anchored to measured BaZrS3 thin-film transport and defect ranges and to a recent high-performance CZTSSe device. Under the favorable n-type top-absorber boundary, optical/electrical co-optimization moves the BaZr0.85Ti0.15S3 thickness from 0.90 μm to 0.05 μm and gives 3.30% from the top cell plus 13.56% from the filtered bottom cell, for a 16.86% four-terminal efficiency. A 1200-sample material/contact uncertainty analysis at this thickness gives P5, median, and P95 efficiencies of 8.07%, 10.73%, and 15.49%, respectively. An additional 55-case direct SCAPS sweep over donor density, bulk defect density, minority-hole mobility, and trap capture cross section, together with maximum-power-point depth profiles, identifies defect-mediated recombination and minority-hole collection as the controlling top-cell constraints. The results show that the proposed absorber pair remains scientifically interesting, but its performance is controlled by minority-hole transport, sulfur-vacancy-related n-type doping, top-cell thickness, bottom-cell material quality, and contact resistance. Accordingly, 33.93% should be interpreted as a long-term material-quality ceiling rather than an experimentally credible near-term prediction.
SN - 2045-2322
ER -