Inverted (p-i-n) perovskite solar cells (PSCs) have surged past 27% certified power conversion efficiency, approaching the Shockley–Queisser limit. Yet their real-world deployment faces a formidable bottleneck: operational stability under reverse-bias stress—a condition triggered when partial shading forces individual cells into reverse polarity, inducing localized overheating and catastrophic degradation. Conventional stabilization strategies predominantly target surface passivation or bulk additive engineering, addressing symptomatic consequences rather than the root cause. Emerging evidence reconceptualizes perovskite lattice strain not as a passive byproduct, but as a fundamental driver of intrinsic instability that lowers ion migration barriers and promotes defect nucleation. Now, researchers led by Niqian Du, Shanshan Du, Yaru Du, Xiaobo Zhang, Zhiyong Liu, and Kaikai Liu have developed a transformative buried interface engineering strategy that directly tames lattice strain at its origin—the hole-transport-layer/perovskite interface—delivering exceptional efficiency and unprecedented resilience under the harshest operational conditions.
Innovative Design and Mechanism
The team identified the buried HTL/perovskite interface as the principal site of strain accumulation, where poor nucleation templates generate mismatched crystallization and propagate structural defects throughout the perovskite bulk. To engineer this critical interface, they incorporated 3-fluorothiophene-2-carboxylic acid (3F-2TC) into the self-assembled monolayer (SAM) HTL, creating a multifunctional molecular modifier that operates across three synergistic dimensions.
First, 3F-2TC disrupts the amphiphilic self-aggregation of MeO-4PACz SAM molecules via hydrogen bonding interactions, guiding their ordered assembly on ITO and forming a uniform, pinhole-free HTL with enhanced coverage (In–O–P/In–O–H ratio increased from 12.63% to 17.35%). This optimized HTL exhibits improved conductivity, favorable energy-level alignment (Fermi level downshift reducing interfacial barriers), and enhanced hydrophobicity (water contact angle: 68.28° vs. 53.02°).
Second, the electronegative moieties of 3F-2TC—fluorine (–F) and carbonyl (C=O) groups—establish dual chemical passivation at the buried interface. FTIR spectroscopy confirms C=O coordination with undercoordinated Pb 2+ ions (red-shift from 1649 to 1658 cm -1 ), while N–H···F hydrogen bonding stabilizes FA⁺ cations. XPS reveals distinct down-shifts in Pb 4f and I 3d binding energies, evidencing robust Lewis acid–base interactions that suppress deep-level trap states.
Third, and most critically, this buried interface engineering directly templates perovskite crystallization toward a low-strain lattice. DFT calculations demonstrate that 3F-2TC incorporation promotes Pb-I-Pb bond angles closer to the ideal 180° (170±3° vs. 163±4° for control), facilitating a structurally relaxed perovskite framework. Grazing-incidence X-ray diffraction (GIXRD) unambiguously confirms this strain release: the control film exhibits a substantial 2θ-sin 2 ψ slope of −3.583×10 -2 , indicating considerable residual stress, while the target film achieves a near-zero slope of −1.418×10 -2 , signifying dramatically reduced lattice distortion.
Outstanding Performance
The champion target device achieves a remarkable power conversion efficiency of 26.10% (Voc = 1.19 V, Jsc = 25.56 mA cm -2 , FF = 85.80%), surpassing the control (24.91%) with substantially reduced hysteresis index (1.9% vs. 3.7%). Statistical analysis across 20 devices confirms superior reproducibility. The integrated current density from EQE spectra aligns precisely with J–V measurements, validating reliability.
Crucially, the team utilized reverse-bias stress as a diagnostic probe to decouple strain relaxation from mere defect passivation—a pivotal experimental design that unambiguously assigns enhanced stability to the robust perovskite lattice. Under −1.0 V reverse bias in N₂, the target device retains 91.58% of initial PCE after 200 hours, while the control plummets to 73.84%. Notably, after an initial 8-hour PCE drop, the target device exhibits almost complete self-recovery after overnight dark storage, demonstrating exceptional resilience. XRD analysis under reverse bias reveals the control's (100) peak FWHM broadening from 0.114 to 0.152, while the target shows minimal change (0.110 to 0.123), confirming superior crystallization stability.
The ion migration activation energy increases from 0.47 eV (control) to 0.63 eV (target), indicating effective suppression of strain-facilitated ion transport. Trap density drops from 4.04×10 15 cm -3 to 3.21×10 15 cm -3 , with carrier lifetime extending from 466.37 ns to 648.66 ns.
Beyond reverse-bias resilience, the target devices demonstrate comprehensive stability across multiple accelerated-aging protocols: 80.81% PCE retention after 500 hours at 85°C (vs. 61.60% for control), and 90.43% retention after 1,600 hours of continuous 1-sun illumination at 35% relative humidity (vs. 71.69% for control). The fluorine-containing modifier enhances surface hydrophobicity, contributing to moisture resistance.
The universality of this strategy is validated across diverse SAM architectures (MeO-2PACz, Me-4PACz) and perovskite compositions (1.54 eV regular bandgap, 1.68 eV and 1.78 eV wide bandgap), consistently enhancing device performance.
Applications and Future Outlook
This work establishes buried interface engineering for lattice strain modulation as a generalizable design principle that moves beyond conventional defect-passivation paradigms to address the root cause of perovskite instability. By demonstrating that a low-strain lattice constitutes the primary defense against bias-induced degradation, this "strain-first" approach provides a foundational strategy for next-generation photovoltaics combining high efficiency with operational resilience. The exceptional performance under reverse-bias conditions—directly relevant to partial-shading scenarios in real-world modules—positions this technology as a critical enabler for the commercialization of inverted perovskite solar cells and tandem architectures.
Stay tuned for more groundbreaking research from this collaborative team at Henan Normal University, Henan University of Science and Technology, City University of Hong Kong, and Hebei University!
Nano-Micro Letters
News article
Taming Lattice Strain via Buried Interface Engineering for Reverse‑Bias Resilient Perovskite Solar Cells
27-May-2026