Zixu Huang

Inverted perovskite solar cells have achieved substantial efficiency gains owing to advances in surface passivation; as a result, progress is now limited by buried defects at the perovskite/hole transport layer (HTL) interface. During top-down perovskite crystallization, the downward film-closure front eventually reaches precursor-phobic, low-surface-energy HTLs in a regime of severe local solution depletion, leading to interfacial solution cavities that then evolve into defects and voids, an issue that becomes increasingly pronounced with larger device areas. We hypothesize that pre-embedding adhesion-enhancing molecules at the HTL surface could trigger early buried-interface crystallization. This could produce solidification on a precursor-affine, homogeneous perovskite-terminated surface, preventing solution cavities and suppressing void formation. We explore a series of substrate-anchored crystallization accelerators, among which structures featuring isothiouronium templating groups we find to be the most impactful in promoting ionic assembly, strengthening substrate–precursor interactions, and accelerating crystallization at the buried interface, which allows final film coalescence to occur on a precrystallized perovskite surface. The strategy enables a void-suppressed buried interface with 8-fold lower defect density and a 1.5× increase in the yield of radiative recombination, enabling uniform performance across centimeter-scale areas. The resulting devices have certified quasi-steady-state power conversion efficiencies of 26.8% and 25.2% for 0.05 and 1.03 cm2 illuminated areas, respectively, and retain 80% of their initial efficiency after 1200 h of operation at 85 °C and 50% relative humidity.

Previous studies of reverse-bias stability in perovskite solar cells have focused primarily on voltage-controlled tests. Here, we instead investigate 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 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 phosphonic-acid interface layer MeO-2PACz, with poorer indium-doped tin oxide (ITO) coverage compared to PTAA, exhibit gradual and recoverable degradation under certain stress and recovery 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 degradation than higher currents over shorter periods. Combining electrical measurements with spatially resolved photoluminescence imaging, our observations support an ion- and charge-mediated interfacial electrochemical degradation mode.

We explore silane-coated formamidinium lead bromide (FAPbBr₃) quantum dots (QDs) as single photon emitters and compare them to FAPbBr₃ QDs passivated with a phosphoethylammonium derivative (PEAC₈C₁₂), which represents current state-of-the-art ligand passivation. We compare properties including single-photon purity (g⁽²⁾(τ)), line width, blinking, and photostability. We find that at room temperature, these silane-coated dots perform comparably to PEAC₈C₁₂-passivated dots, while exhibiting improvements in photostability. However, we find that at 4 K, silane-coated FAPbBr₃ QDs 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 nonradiative processes in the silane-coated QDs at 4 K. We propose a trion-related degradation pathway at low temperatures that is consistent with the observed kinetics and estimate that at 4 K with 6.1 μJ/cm², 472 nm excitation the silane-coated QDs build up double the trion population of their PEAC₈C₁₂-passivated counterparts.

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 FA_0.78Cs_0.22Pb(I_0.85Br_0.15)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, overexposure, 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.