arXiv subjects

Zixu Huang

Publications and source records attributed to Zixu Huang.

4 recordsLinked to original sources

arXiv2026

Degradation Dynamics of Perovskite Solar Cells Under Fixed Reverse Current Injection

Previous studies of reverse-bias stability in perovskite solar cells have focused primarily on voltage controlled reverse-bias tests. Here we instead present an investigation of perovskite solar cell degradation under well-defined, constant reverse-current stress. We show that the choice of hole-transport layer dictates the dominant degradation pathway: cells using thick poly(triphenylamine) (PTAA) layers with better indium-doped tin oxide (ITO) coverage can tolerate high reverse bias but quickly undergo catastrophic breakdown under fixed reverse current near their one-sun maximum power-point. In contrast, cells modified with the phosphonic-acid interface layer MeO-2PACz, with poorer ITO coverage compared to PTAA, exhibit soft, gradual, and largely recoverable degradation, regardless of the shading conditions. For MeO-2PACz devices, degradation increases with both current magnitude and duration. Importantly, when normalized by injected charge (current times duration), lower currents applied over longer times cause more severe degradation than higher currents over shorter periods. Combining electrical measurements with spatially resolved photoluminescence imaging, we argue against shunt formation and instead support an ion- and charge-mediated interfacial electrochemical degradation mode.

physics.app-ph↗

arXiv2025

Trion Formation Hampers Single Quantum Dot Performance in Silane-Coated FAPbBr3 Quantum Dots

We explore silane-coated formamidinium lead bromide (FAPbBr3) quantum dots as single photon emitters and compare them to FAPbBr3 quantum dots passivated with a phosphoethylammonium derivative (PEAC8C12), which represents current state-of-the-art in zwitterionic molecular surface ligand passivation. We compare properties including single-photon purity (g2(t)), linewidth, blinking, and photostability. We find that at room temperature, these silane-coated dots perform comparably to the PEAC8C12 passivation in terms of single-photon performance metrics, while exhibiting improvements in photostability. However, we find that at 4K, silane-coated FAPbBr3 quantum dots perform worse than the PEAC8C12-passivated samples, exhibiting faster blue-shifting and photobleaching under illumination. Analysis of fluorescence lifetime intensity distributions from the photon-counting data indicates increased efficiency of fast non-radiative processes in the silane-coated quantum dots at 4K. We propose a trion related degradation pathway at low temperatures that is consistent with the observed kinetics and estimate that at 4K with 6.1 uJ/cm2, 472 nm excitation the silane-coated quantum dots build up double the trion population of their PEAC8C12-passivated counterparts.

cond-mat.mtrl-sci↗

arXiv2025

Comparing Machine Learning and Physics-Based Nanoparticle Geometry Determinations Using Far-Field Spectral Properties

Anisotropic metal nanostructures exhibit polarization-dependent light scattering. This property has been widely exploited to determine geometries of subwavelength structures using far-field microscopy. Here, we explore the use of variational autoencoders (VAEs) to determine the geometries of gold nanorods (NRs) such as in-plane orientation and aspect ratio under linearly polarized dark-field illumination in an optical microscope. We input polarized dark-field scattering spectra and electron microscopy images into a dual-branch multimodal VAE with a single shared latent space trained on paired spectra-image data, using a learnable linear adapter. We achieve prediction of Au NRs using only polarized dark-field scattering spectra input. We determine geometrical parameters of orientational angle and aspect ratio quantitatively via both dual-VAE and physics-based analysis. We show that orientational angle prediction by dual-VAE performs well with only a small (300 particle) training set, yielding a mean absolute error (MAE) of 14.4 and a concordance correlation coefficient (CCC) of 0.95. This performance is only marginally worse than the physics-based cos(2theta) fitting approach between the scattering intensity and the polarizing angle, which achieves MAE of 8.78 and CCC of 0.99. Aspect ratio determination is also similar for the dual-VAE and physics-based fitting comparison (MAE of 0.21 vs. 0.23 and CCC of 0.53 vs. 0.68). By learning a shared latent manifold linking spectra and morphology, the model can generate NR images with accurate orientation and aspect ratio with spectra-only input in the small-data regime (300 particles), suggesting a general recipe for inverse nano-optical problems requiring both structure and orientation information.

physics.optics↗

arXiv2025

Surface Passivation for Halide Optoelectronics: Comparing Optimization and Reactivity of Amino-Silanes with Formamidinium

Amino-silane-based surface passivation schemes are gaining attention in halide perovskite optoelectronics, with varying levels of success. We compare surface treatments using (3-aminopropyl)trimethoxysilane (APTMS) and [3-(2-aminoethylamino)propyl]trimethoxysilane (AEAPTMS), applied via room-temperature vacuum deposition, to the perovskite FA0.78Cs0.22Pb(I0.85Br0.15)3 (FA = formamidinium). Both molecules improve thin-film photoluminescence properties and photovoltaic device performance, although their effectiveness depends strongly on deposition time. We show AEAPTMS has a wider, more robust processing window and yields higher performance under optimized conditions. In contrast, over-exposure, particularly with APTMS, reduces performance, with notable reductions in photoluminescence lifetime and absorbance. To probe the underlying chemistry, we employ nuclear magnetic resonance (NMR) spectroscopy and depth-resolved time-of-flight secondary ion mass spectrometry (ToF-SIMS), demonstrating that both amino-silanes react with formamidinium (FA+) cations in solution and in the solid state. This work underscores the importance of optimizing deposition conditions to balance effective passivation with potential performance loss and elucidates previously unrecognized reactive chemistry between amino-silane passivating agents and halide perovskites.

cond-mat.mtrl-sci↗