Wei Zhang

End-group isomerization of polymerized small-molecule acceptors can enhance exciton diffusion length in neat acceptor films, and accelerate CT-state dissociation while suppressing carrier recombination in the corresponding blend films.

Achieving efficient charge transport while maintaining low nonradiative energy loss remains a key challenge in the molecular design of small‐molecule acceptors (SMAs) for organic solar cells (OSCs). Herein, we report a stepwise molecular engineering strategy based on sulfur locking and chlorination to regulate intermolecular packing and excited‐state properties simultaneously. Sulfur locking modifies molecular conformation and intermolecular packing, leading to enhanced exciton diffusion and charge transport. Subsequent chlorination further strengthens intermolecular interactions through additional Cl···S contacts, resulting in tighter π–π stacking and improved crystalline ordering. Binary OSCs based on D18:Qx2Ph‐SCl achieve an efficiency of 20.0% with a high open‐circuit voltage ( V _OC ) of 0.951 V, while maintaining a low nonradiative energy loss of ∼0.19 eV. Owing to its intrinsically lower reorganization energy and weaker electron–phonon coupling than L8‐BO, Qx2Ph‐SCl further serves as an effective third component in ternary OSCs, reducing nonradiative recombination and increasing the V _OC . As a result, the ternary device delivers an efficiency of 21.3%. This work demonstrates that stepwise sulfur locking and chlorination provide an effective molecular design strategy for simultaneously optimizing charge transport and voltage loss in high‐performance OSCs.

Group velocity mismatch (GVM) and phase matching are core concepts in nonlinear optics and ultrafast physics curricula, yet undergraduate students are frequently introduced through mathematical derivations of the walk-off length formula, without a direct experimental analogue that builds physical intuition. Meanwhile, conventional femtosecond third-harmonic generation (THG) setups employ non-collinear geometries and complex temperature control, making them impractical for student-operated laboratory sessions. To address this pedagogical gap, we present a modular, fully collinear femtosecond THG system designed specifically for upper-division undergraduate laboratory education. The system uses two β-BaB2O4 (BBO) crystals for sequential frequency doubling and sum-frequency generation under Type-I phase matching, with a precision optical delay line as the key pedagogical control element. By scanning the delay line position and monitoring the 266 nm THG signal, students transform the abstract concept of GVM into an observable, quantifiable experimental variable. The collinear design reduces optical alignment to a single-axis operation, enabling students to complete assembly, calibration and data acquisition within a single 3–4 h laboratory session. The system achieves a THG conversion efficiency of 2.47%, which is comparable to typical dual-crystal cascaded THG systems, with a central wavelength of 266.8 nm (FWHM 4.6 nm), sufficient for subsequent transient spectroscopy experiments. All components are standard off-the-shelf optics, and the modular architecture allows flexible adaptation by other institutions. The system has been validated through Training Project for College Students, demonstrating its suitability for inquiry-based learning in advanced physics laboratory courses.

Exciton diffusion to donor–acceptor interfaces plays a critical role in charge generation in organic solar cells, yet its dependence on film fabrication and operating temperature remains poorly understood for high-performance nonfullerene acceptors. Here, femtosecond transient absorption spectroscopy and exciton–exciton annihilation analysis quantify diffusion in Y6 and L8-BO. In Y6 films, processing changes the diffusion coefficient (D) from 0.4 × 10–2 to 1.3 × 10–2 cm2 s–1 and the diffusion length (Ld) from 16.9 to 37.4 nm, whereas L8-BO maintains substantially more stable exciton diffusion across processing conditions. Cooling markedly decreases D and Ld despite a prolonged exciton lifetime, consistent with reduced thermally assisted exciton hopping in an energetically disordered environment. In PM6:Y6 blends, processes related to bimolecular charge recombination slow down with decreasing temperature. These results highlight molecular packing, energetic disorder, and temperature as key factors controlling exciton diffusion and charge dynamics in Y-series acceptors, providing a mechanistic framework for optimizing exciton harvesting in nonfullerene organic solar cells.

Organic solar cells (OSCs) have achieved remarkable progress, yet improving exciton utilization in polymer donors remains challenging due to their intrinsically limited exciton diffusion length ( L _D ). Here, we report a donor‐selective templating strategy based on few‐layer‐like nickel–cobalt layered double hydroxide (NiCo‐LDH) nanosheets to regulate polymer donor assembly in OSCs. The hydroxyl‐rich NiCo‐LDH surface exhibits preferential affinity toward polymer donors and promotes ordered donor‐chain organization during film formation, while exerting limited influence on the acceptor component. This templating strategy enhances the molecular ordering of the donor phase and increases the L _D of D18 from 10.7 to 18.9 nm, accompanied by the formation of more ordered donor fibrillar structures. The coordinated improvements in donor organization and exciton transport are further associated with enhanced exciton‐to‐charge conversion, more balanced carrier transport, and suppressed recombination. Consequently, D18:L8‐BO‐based OSCs achieve a maximum power conversion efficiency (PCE) of 21.36%, independently certified at 21.09%, together with improved stability under continuous illumination. Analogous donor‐biased interactions, enhanced exciton diffusion, regulated fibrillar organization, and improved photovoltaic performance are also observed in PM6 and D18‐Cl systems. These results highlight the broader applicability of chemically active 2D templating for coordinating polymer donor assembly and exciton transport toward high‐performance OSCs.

In this study, we report a porphyrin-based metallo-organic cage (Por-Cage) for efficient, selective photocatalytic detoxification and sulfide oxidation under air, offering a new strategy for high-performance porphyrin photocatalysts.

Mixed‐ion perovskites have attracted wide attention in optoelectronic applications due to their exceptional properties, such as tunable bandgaps and long carrier diffusion lengths. Carrier mobility is a critical factor for determining the performance of optoelectronic devices. However, the substantial variation in reported mobility values has hindered a comprehensive understanding of charge transport in mixed‐ion perovskites. In this work, we conducted time‐domain Brillouin scattering measurements to characterize the elastic constants and deformation potentials of electrons/holes in FA _x MA _1−x PbBr ₃ single crystals. We find that the elastic constants of crystals decrease with the increase of FA content. Applying deformation potential theory to these measured parameters, we determined the intrinsic carrier mobility determined by carrier‐acoustic phonon coupling, and revealed high intrinsic electron and hole mobilities in FA _x MA _1−x PbBr ₃ single crystals. We also find that both electron and hole mobilities, determined by carrier‐acoustic phonon coupling, decrease with the increase of FA content in FA _x MA _1−x PbBr ₃ single crystals. This work advances the comprehension of intrinsic carrier transport properties and offers essential guidance for the rational design of high‐performance perovskite materials.

Polythiophenes are the most promising electron donors for organic solar cells (OSCs) in large-scale manufacturing owing to their simple chemical structures and low production costs. However, the efficiency of polythiophene solar cells is largely limited because of the difficulty in morphology optimization. Herein, we report the construction of a refined fibril network structure in polythiophene:non-fullerene acceptor blends based on the classical nucleation theory. By screening solvents for polythiophene to obtain an appropriate nucleation driving force while ensuring that the non-fullerene acceptor does not over-crystallize, a refined crystalline fibril network morphology was obtained in the blend consisting of a structurally simple polythiophene P5TCN-HD and a non-fullerene acceptor. This optimal morphology improved exciton dissociation and charge transport, thereby endowing the solar cells with an unprecedented power conversion efficiency of 18.12% and a fill factor of 79.17%, marking new breakthroughs for polythiophene-based OSCs. Notably, these results were achieved using toluene as the solvent, which is a common non-halogenated and environmentally benign solvent. Moreover, the crucial impact of solvent quality on the formation of the fibril network structure was revealed, offering valuable insights for optimizing the morphology of polythiophene systems. This underscores the promising prospect of polythiophenes in developing high-efficiency yet low-cost OSCs via environmentally benign processing, driving the industrialization of OSCs.