Fluorinated Monolayers Balance Passivation and Charge Transport in Perovskite Solar Cells
Fluorinated self-assembled monolayers can optimize hole transport layer stability while balancing interfacial defect passivation and charge transport in perovskite solar cells, according to quantum chemical calculations and numerical device simulations. Researchers evaluated donor-acceptor type self-assembled monolayers based on the 3-(7-(4-(bis(4-methoxyphenyl)amino)phenyl)benzo[c][1,2,5]thiadiazol-4-yl)-2-cyanoacrylic acid molecule, commonly designated as MPA-BT-CA, to identify how progressive fluorination modulates electronic and interface performance in photovoltaic architectures.
Using density functional theory and time-dependent density functional theory alongside one-dimensional SCAPS-1D device modeling, the team investigated the electronic, optoelectronic, non-linear optical, and thermodynamic behavior of the modified organic molecules. The theoretical findings showed that introducing fluorine substituents does not significantly alter the vibrational modes of the core MPA-BT-CA framework, but it establishes a defined physical trade-off between interfacial passivation capabilities and intrinsic charge transport dynamics.
The quantum calculations revealed that difluorination to produce 2FMPA-BT-CA alters the fundamental molecular orbital energy levels of the assembly. Specifically, the energy of the lowest unoccupied molecular orbital decreased from -3.17 eV to -3.34 eV, while the highest occupied molecular orbital energy shifted from -5.24 eV down to -5.36 eV.
Alongside the orbital shifts, difluorination increased the molecular reorganization energy, which constrained the calculated intrinsic hole mobility of the 2FMPA-BT-CA monolayer to 4.10e-3 cm2 V-1 s-1. Concurrently, the modification maximized the non-linear optical response, yielding an 8.38 percent increase in molecular hyperpolarizability, alongside improved structural stability for the passivating layer.
Despite the observed decrease in hole transport parameters as fluorine content increased, the difluorinated variant exhibited pronounced interfacial properties. The 2FMPA-BT-CA molecule demonstrated a very high effective state density NV of 62.02e20 cm-3 and superior chemical reactivity indices, pointing to a strong physical capacity for passivating defect sites located at the perovskite interface.
When simulated within a complete perovskite solar cell architecture based on a MA0.5FA0.5PbI3 absorber layer using SCAPS-1D software, the device incorporating the 2FMPA-BT-CA monolayer achieved a power conversion efficiency of 20.25 percent.
In contrast to the difluorinated configuration, the monofluorinated FMPA-BT-CA molecule presented an alternative performance profile. The monofluorinated structure offered a superior compromise across optoelectronic metrics, displaying ultraviolet-visible absorption features, a dipole moment, and a refractive index that aligned more closely with the optical characteristics of the perovskite absorber material.
By using density functional theory and time-dependent density functional theory, the researchers evaluated the influence of fluorination across thermodynamic stability, vibrational modes, and optoelectronic indices.
The comparative data reveal an explicit divergence in design priorities between monofluorinated and difluorinated configurations. While progressive fluorination systematically degrades hole transport parameters, the difluorinated molecule compensates through an 8.38 percent gain in hyperpolarizability and superior chemical reactivity indices, suggesting enhanced capacity for passivating interfacial defects. Conversely, the monofluorinated structure resolves this trade-off by avoiding severe transport penalties and instead optimizing optical compatibility, displaying a closer refractive index match with the perovskite absorber alongside favorable dipole moment and ultraviolet-visible absorption characteristics.
Regarding scope and limitations, these findings reflect predictive quantum modeling and numerical simulations rather than empirically measured device prototypes. The 20.25 percent power conversion efficiency was calculated through one-dimensional SCAPS-1D simulation specifically for a MA0.5FA0.5PbI3 perovskite architecture, meaning the modeled performance serves as a theoretical benchmark.
Subject of Research: Computational modeling of fluorinated self-assembled monolayers for perovskite solar cells
Article Title: Fluorinated MPA-BT-CA self assembled monolayers for perovskite solar cells balancing interfacial passivation and charge transport investigated by DFT and SCAPS-1D simulation
Article References: Banka, N. C. T., Fomekong, L. T., Ngoupo, A. T., Abe, M. T. O., Ngue, P. G. D. K., Eone II, R. J., & Ndjaka, J. M. B. (2026). Fluorinated MPA-BT-CA self assembled monolayers for perovskite solar cells balancing interfacial passivation and charge transport investigated by DFT and SCAPS-1D simulation. Discover Applied Sciences. https://doi.org/10.1007/s42452-026-09790-9
Image Credits: AI Generated
DOI: 10.1007/s42452-026-09790-9
Keywords: perovskite solar cells, self-assembled monolayers, MPA-BT-CA, hole transport layers, density functional theory, SCAPS-1D, fluorination, charge transport, interfacial passivation, power conversion efficiency, molecular hyperpolarizability, frontier molecular orbitals, photovoltaic devices, reorganization energy, effective state density, optoelectronic properties
News Source: Denise Maddox. (November 13, 2026). Fluorinated Monolayers Balance Passivation and Charge Transport in Perovskite Solar Cells. Scienmag.
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