Publication date: 22nd July 2026
Understanding the α-phase stability of FACsPbI₃ in halide perovskite/MXene heterojunctions for Carbon based perovskite solar cells
Zait Ayalaa,b, Ramses Mirandaa, Juan Dávalosc and Monica Lira*a
- Catalan Institute of Nanoscience and Nanotechnology (ICN2), CSIC and the Barcelona Institute of Science and Technology (BIST), Building ICN2, Campus UAB, E-08193 Bellaterra, 08193, Barcelona, Spain.
- Universidad Nacional de Ingeniería (UNI).
- Instituto de Química-Física “Blas Cabrera”, CSIC, Serrano 119, 28006 Madrid, Spain.
Corresponding autor: monica.lira@icn2.cat
Formamidinium–cesium lead iodide (FACsPbI₃) perovskite solar cells (PSCs) are promising candidates for next-generation photovoltaics owing to their near-optimal bandgap (~1.56 eV), excellent optoelectronic properties, and reduced susceptibility to halide segregation. However, residual lattice strain and interfacial defects accelerate the transformation of the photoactive α-phase into the non-photoactive δ-phase under ambient conditions, thereby limiting long-term operational stability.
In this work, we fabricate carbon-based FACsPbI₃ PSCs entirely under ambient atmosphere (19–21 °C, 50–60% RH) by incorporating a 2D Ti₃C₂Tₓ MXene–PEAI hybrid interlayer between the perovskite absorber and the hole transport layer. Delaminated Ti₃C₂Tₓ MXene was prepared via TPAOH-assisted intercalation and subsequently functionalized with phenethylammonium iodide (PEAI) to simultaneously passivate interfacial defects, relieve residual strain, and stabilize the α-phase of FACsPbI₃.
Fourier-transform infrared (FTIR) spectroscopy confirms the interaction between PEAI and MXene through a red shift of the N–H stretching vibration. X-ray diffraction (XRD) verifies the formation of phase-pure α-FACsPbI₃ with enhanced crystallinity following thermal optimization, while scanning electron microscopy (SEM) reveals enlarged grains resulting from MACl-assisted crystallization. UV–Vis spectroscopy shows that the optical bandgap remains unchanged at 1.56 eV. Our results demonstrate that the engineered halide perovskite/MXene:PEAI interface markedly improves charge-carrier dynamics. Time-resolved photoluminescence (TRPL) measurements show an increase in the average carrier lifetime from 19.88 ns for the control device to 103 ns after PEAI treatment. Electrochemical impedance spectroscopy (EIS) further reveals increased recombination resistance, indicating more effective defect passivation and suppressed non-radiative recombination. In addition, incident photon-to-current efficiency (IPCE) measurements demonstrate enhanced charge-collection efficiency. Carbon-electrode devices achieved power conversion efficiencies (PCEs) of up to 17%, while reference Au-electrode devices incorporating the MXene:PEAI interlayer exceeded 20%. Overall, this interfacial engineering strategy provides a promising route toward scalable, low-cost, and highly stable perovskite solar cells fabricated entirely in air.
This work was subsidized by CONCYTEC and PROCIENCIA under the framework of the contests E077-
2023-01-BN ‘Scholarships in Doctoral Programs in Interinstitutional Alliances’
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