Zihao Xu

Photon upconversion based on triplet–triplet annihilation can utilize incoherent sub-bandgap photons for energy conversion and photocatalysis. Though quantum dots (QDs), with their tunable bandgaps, make attractive triplet photosensitizers, energy transfer must compete with other exciton-depleting pathways that stem from various trap states. Here, we show that strong electronic coupling can be introduced through conjugated bridges between Si QDs and surface-bound pyrene acceptors by creating a transient hole-transfer intermediate from Si to attached pyrenes, which enhances triplet energy transfer. The hybrid achieved an upconversion quantum yield of 10.8% (with a theoretical maximum of 50%) with DPA as the emitter, which is the highest reported for Si QD-based upconversion. By using a combination of cyclic voltammetry, time-resolved electron paramagnetic resonance, and transient absorption spectroscopies, we show that the alkyne and vinyl bridges hybridize QD and molecular states, facilitating hole-then-electron transfer that competes effectively with exciton quenching. Specifically, the alkyne-linked Si QD: AP hybrid exhibits hole transfer with a time constant of 1.7 ns and an efficiency of 27%, highlighting linker conjugation as an effective strategy for overcoming unfavorable kinetics and energetics.

Directing photogenerated carriers toward productive coupled redox chemistry is central to solar-to-chemical energy conversion, yet the interfacial chemical basis governing carrier routing remains elusive. Here, we establish a hydroxyl-defined Lewis base interface as a chemically programmed platform for coupling hole-selective extraction with cooperative photoredox catalysis. By in situ constructing crystalline In(OH)3 on ultrathin ZnIn2S4 nanosheets (ZISO), a hydroxyl-associated interfacial architecture enriched with lattice hydroxyl Lewis base sites is created, enabling selective regulation of oxidation-side carrier dynamics. Femtosecond transient spectroscopic and surface photovoltage measurements reveal that the hydroxyl-defined interface promotes hole-selective interfacial extraction, suppresses charge recombination, and preserves reduction-side electron population for the reduction reaction. Consequently, photooxidative thiophenol valorization via dehydrogenative coupling proceeds at a rate of 33.5 mmol g–1 h–1 and is efficiently integrated with CO2 photoreduction in a cooperative photoredox process. Density functional theory calculations further show that the hydroxyl-defined interface generates cooperative adsorption configurations that promote electronic polarization and substrate activation, stabilize key reaction intermediates, and lower the energetic requirements for CO2 reduction. As a result, the hydroxyl-defined interface translates directional carrier dynamics into interfacial redox turnover, enabling efficient cooperative photoredox catalysis. This work reveals that chemically explicit interfacial functionality can be leveraged to integrate carrier-selective routing and catalytic redox chemistry, providing an interfacial design principle for cooperative photoredox systems in solar-to-chemical energy conversion.

Triplet–triplet annihilation upconversion sensitized by quantum dot is often limited by the short exciton lifetime, necessitating tethered triplet transmitter. Here, we report a transmitter-free system of ZnSe quantum dot and 2,5-diphenyloxazole achieving 24% upconversion quantum yield, the highest for quantum dot sensitization upconversion. The upconversion quantum yield peaks at 30 mM 2,5-diphenyloxazole. Transient spectroscopy shows the triplet energy transfer efficiency is over 80% regardless of the 2,5-diphenyloxazole concentration, but the triplet–triplet annihilation efficiency dominates the overall upconversion quantum yield and shows a strong dependence on the 2,5-diphenyloxazole concentration that increases first from 10% to 25%, then decreases. The optimal concentration is achieved when the triplet 2,5-diphenyloxazole collision probability is highest, thus ensuring a maximum triplet–triplet annihilation efficiency. This work demonstrates a design principle of binary quantum dot upconversion system and reveals the critical role of modulating emitter concentration for optimal upconversion quantum yield.

The construction of valuable 3D molecular architectures from easy-to-handle stable bulk chemicals has long been a target in chemical society. However, the highly reactive intermediates generated in situ pose significant challenges for achieving enantioselective control. To address these challenges, novel catalysts must be developed. This report describes a multifunctional vanadium electrophotocatalyst that serves as a photosensitizer and C(sp³)-H activation catalyst precursor to activate protic C(sp³)-H bonds. Notably, it also acts as a chiral metal catalyst to enable enantioselective control. The optimized protocol tolerates a diverse array of readily available feedstocks (e.g., acetone, acetonitrile, dichloromethane) with various functional groups, which can be enantioselectively incorporated onto a C═C double bond at looxidation potential (around 0.40 V vs Ag/AgCl). The nonclassical toolkit described herein is characterized by high sustainability, diverse protic C(sp³)-H compounds, and excellent enantioselectivity without requiring external chemical oxidants, thus opening new synthetic routes via unique reactivities.

Organic solar cells hold great promise for next-generation photovoltaics, yet their practical deployment is impeded by intrinsic morphological and interfacial limitations that compromise device performance and stability. Herein, we introduce a vacuum-induced interfacial compaction strategy that forms smooth, compact, and strongly adhered multilayer films without conventional thermal or solvent annealing, by promoting dense stacking, suppressing interfacial voids, and improving overall interfacial integrity. Consequently, corresponding devices achieve power conversion efficiencies of 20.51% for rigid and 19.13% for flexible devices, together with a high yield. Notably, device with an active area of 1.0 cm² and a module with an area of 15.7 cm² fabricated with this strategy deliver efficiencies of 19.04% and 17.48%, respectively. Upon further scaling the module area to 67.2 cm², a high efficiency of 15.37% is still attained. These results establish the vacuum-induced interfacial compaction strategy as a feasible route toward durable, high-performance organic solar cells.

Micro-cocrystals of the intermolecular charge-transfer (CT) complex formed from pyrene and tetracyanobenzene can be fabricated via a solution-based method. Intersystem crossing of the directly excited CT exciton in the cocrystal is observed, yielding a CT triplet exciton that undergoes efficient triplet-triplet energy transfer to a diphenylanthracence (DPA)-based triplet acceptor. For the first time, we demonstrate that these micro-cocrystals can act as triplet sensitizers to upconvert the emission of liquid-state DPA triplet acceptors, enabling highly efficient triplet-triplet annihilation photon upconversion (TTA-UC) from 532 to 430 nm. This work demonstrates the utilization of CT excitons as triplet sensitizers in a TTA-UC process, providing a novel approach for efficient and heavy-atom-free UC systems.

The cathode interfacial layer (CIL) critically influences electron extraction and charge recombination, thereby playing a pivotal role in organic solar cells (OSCs). However, most state-of-the-art CILs are constrained by limited conductivity, high recombination and poor morphology, which collectively hinder device efficiency and stability. Here we report an inorganic-organic hybrid CIL (AZnO-F3N), developed by a dual-component synergy strategy, which integrates organic material PNDIT-F3N with two-dimensional amorphous zinc oxide. This design leverages the synergistic interactions between two-dimensional amorphous zinc oxide and PNDIT-F3N, resulting in reduced interfacial defect, enhanced conductivity and improved film uniformity. OSCs incorporating the AZnO-F3N CIL exhibit more efficient charge extraction and transport, along with reduced recombination. Consequently, a D18:L8-BO-based binary OSC achieves an efficiency of 20.6%. The introduction of BTP-eC9 as the third component further elevates the efficiency to 21.0% (certified as 20.8%). Moreover, the CIL demonstrates versatility across various active layers, thick-film configuration and flexible devices, underscoring its great potential to advance OSC technology.

The observation of third-order water oxidation kinetics by Fe^IV=O accumulation at the semiconductor-electrolyte interface is a milestone for understanding the four-electron transfer reaction mechanism. However, the consequences of such Fe^IV=O accumulation for the associated recombination reaction kinetics at the interface have not been fully explored so far. Here, we observe fast second-order recombination reaction kinetics for Fe^IV=O as the result of its accumulation at the model hematite-electrolyte interface, compared to the first-order recombination reaction kinetics for a lesser amount of available Fe^IV=O. We refer to this phenomenon as "accumulation-accelerated recombination (AAR)" and highlight the adverse role of Fe^IV=O accumulation at the interface. Further, we demonstrate that this fast second-order AAR could be slowed down to first-order kinetics by (i) deprotonation of the metal oxide surface; (ii) evacuating the conduction band electrons; and (iii) partial substitution of Fe^IV=O with less active Co^IV=O species. Such an insight is vital not only for understanding the efficiency loss mechanisms at the semiconductor-electrolyte interface but also for interpreting the interfacial behavior of photovoltaic systems and photocatalysts.

For many slow solar-fuel-forming reactions, the accumulation of photogenerated minority carriers on the photoelectrode surface leads to light-induced band edge unpinning, affecting the junction properties by decreasing band bending in the semiconductor space charge layer and increasing the driving force of surface reactions in the electric double layer. In this study, we demonstrate a contactless operando electric field-induced second harmonic generation (EFISH) method for measuring the band bending change (δΔΦ_SCR^L) on photoelectrodes upon photoexcitation. For n-doped rutile TiO₂ water oxidation photoanodes at pH 7, δΔΦ_SCR^L increases at more positive potentials or higher illumination power density until it reaches saturation values. We show that under fast mass transport conditions, δΔΦ_SCR^L is exclusively attributed to the accumulated charged rate-determining species that can be regarded as temporary surface states, and the relationship between the photocurrent and δΔΦ_SCR^L can be well modeled by assuming that hole trap states function as the reaction center. Kinetic isotope experiments identify proton-coupled electron transfer as the rate-determining step and suggest a possible chemical nature of the key intermediate. We demonstrate that light-induced band edge unpinning is a beneficial feature under high illumination conditions for oxygen evolution reaction on TiO₂ because it maintains the photon-to-current conversion efficiency by enhancing the surface reaction driving force, shedding light on the actual device application.