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Reliability-Resolved Ranking of Molecular Additives for Defect-Passivated Mixed-Cation Perovskite Solar Cells

Anthony Leggett1, W. Lee2
1Department of Physics, University of Illinois Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3003, USA
2Shanghai Center for Complex Physics, Shanghai Jiaotong University, Shanghai, People’s Republic of China
Anthony Leggett
Department of Physics, University of Illinois Urbana-Champaign, 1110 West Green Street, Urbana, Illinois 61801-3003, USA
W. Lee
Shanghai Center for Complex Physics, Shanghai Jiaotong University, Shanghai, People’s Republic of China

Abstract

While molecular additives are commonly used for the tuning of crystal growth and defect passivation in halide perovskite solar cells, additive selection is often done based on peak efficiency or chemical intuition. In this paper, we seek to determine whether it is possible to rank additive performance in inverted \(\mathrm{Cs}_{0.05}\mathrm{MA}_{0.10}\mathrm{FA}_{0.85}\mathrm{PbI}_{3}\) devices using the combination of mechanistic analysis, population statistics, champion-cell retention, and trap density suppression via space charge limited current as an objective index. Four molecular additives are analyzed against the raw reference: 3,5-difluoropyridine-2-carboxylic acid (DFCA), 5-hydroxy-2-methylbenzoic acid (HMBA), gallic acid (GA), and caffeic acid (CA). First, a reasoning gate is applied in order to separate the meaningful additive recommendations from superficial pattern-matching. The photovoltaic reliability is calculated via mean \(PCE\), coefficient of variation (\(CV_{PCE}\)), and champion-cell performance. A trap density correction is subsequently applied based on the difference in defect density between the reference and additive-modified devices. Among those additives studied, HMBA yields the strongest total score. It leads to the highest mean \(PCE\) (\(18.20\pm0.27\%\)) and champion \(PCE\) (18.63\%), smallest coefficient of variation (\(1.48%\)), and lowest trap density (\(1.35\times10^{15}\to1.03\times10^{15}~\mathrm{cm^{-3}}\)). The other additives show varied performance, although DFCA also leads to an improvement in defect density. Both GA and CA reduce \(PCE\) and increase the coefficient of variation while failing the reliability requirement despite their multiplicity of polar functional groups.

Keywords: mixed-cation perovskites, additive engineering, defect passivation, trap density, inverted solar cells, reproducibility, reliability index
Copyright © 2026 Anthony Leggett, W. Lee. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.