Quantum Optoelectronics

Abstract:

Lead halide perovskite nanocrystals exhibit excellent optoelectronic properties, yet simultaneous observation of bright singlet and triplet exciton emissions under identical conditions has remained elusive. This limitation hinders optimization of quantum efficiency in light-emitting devices. Here, we provide the direct spectroscopic evidence for coexisting bright singlet and triplet excitons in CsPbBr3 nanocrystals, overcoming the conventional 25 % spin-statistical efficiency ceiling. Using polarization-resolved, spatially resolved, and time-resolved micro-photoluminescence at 7 K, we resolve three sharp triplet fine-structure components (T1, T2, T3) with energy separations of 1–3 meV and linear polarization >85 %, coexisting with broad singlet emission. The triplet emissions display distinct polarization axes, nonlinear intensity scaling, and nanosecond lifetimes, confirming their assignment as Rashba-split bright triplet states. Spatial mapping reveals that these emissions arise from structurally pristine domains with exciton diffusion lengths exceeding 9 μm. Time-resolved measurements show concurrent fast and slow decay components, consistent with singlet-to-triplet intersystem crossing followed by radiative triplet recombination. Our findings establish a comprehensive picture of exciton spin dynamics in perovskite nanocrystals and open new avenues for spin-engineered photonic devices. This work lays the foundation for next-generation LEDs, lasers, and quantum light sources that leverage both singlet and triplet radiative channels to exceed traditional efficiency limits. While these findings are demonstrated at cryogenic temperatures, they highlight essential spin-related mechanisms that could be harnessed for room-temperature operation through enhanced Rashba coupling, dielectric engineering, or compositional tuning.

Abstract:

Photocatalytic ammonia decomposition offers a sustainable route for hydrogen production, but its development is limited by low catalytic efficiency and poorly understood mechanisms. Here, a protonated layered perovskite, HPrNb2O7 (HPNO), is reported as an efficient catalyst for ammonia decomposition under mild photo‐thermal conditions. Upon exposure to NH3 at elevated temperatures, HPNO promotes the in situ formation and intercalation of hydrazine intermediates within its interlayer galleries, enabled by thermally generated oxygen vacancies and hydrogen bonding. Advanced characterization techniques have been applied to confirm the formation and stabilization of hydrazine. It is also shown that thermal energy prolongs charge carrier lifetimes and enhances oxygen vacancy formation, contributing to a strong photo‐thermal synergy. The stabilization of hydrazine intermediate promotes the associative mechanism, lowering the activation barrier, thus leading to an enhanced hydrogen evolution rate of 1311.2 µmol·g−1·h−1 at 200 °C under simulated solar irradiation without any noble metal co‐catalyst. This work reveals a distinct, hydrazine‐mediated reaction pathway and positions layered protonated perovskites as promising materials for efficient, solar‐driven ammonia decomposition and sustainable hydrogen generation.

Abstract:

Achieving stable and efficient circularly polarized luminescence (CPL) from achiral perovskite nanocrystals (PNCs) remains a major challenge in the development of advanced chiroptical materials. Herein, the syntheses of a total of nine compounds, including full‐color colloidal polymer‐capped PNC composites are reported based on organic‐inorganic hybrid perovskites and inorganic 2D nanosheets (NSs) using phenacyl halide as a single organic source of halide precursor. While the initial PNCs exhibit low photoluminescence quantum yield (PL QY) and poor stability, a previously unexplored surface absorption/ion exchange strategy employing 2D‐ZrH2P2O8 NSs significantly enhances both optical properties and long‐term stability, e.g., the FAPbBr3@ZrH2P2O8 (FA = formamidinium) composite exhibits a significantly enhanced PL QY of 88.57%, compared to 30.9% for the pristine counterparts, owing to the protective effect of the robust 2D ZrH2P2O8 network that enhances stability under ambient conditions. Crucially, embedding these stabilized PNCs into a chiral polymer matrix induces distinct mirror‐image strong CPL signals both in solution and solid‐state. This rare dual‐phase CPL activity arises from the conformational adaptability of the chiral polymer, which imparts chirality to the achiral PNCs via both covalent and non‐covalent interactions. These findings present a versatile strategy for producing robust, CPL‐active stable perovskite materials across the visible spectrum for next‐generation chiroptoelectronic devices.

Abstract:

Weakly bonded native ligands severely degrade the performance of perovskite quantum dot (PeQD) light-emitting diodes (LEDs). While conventional approaches can be used to strengthen ligand binding, they fail to achieve complete ligand exchange, leaving residual ligands that promote degradation. Herein, we present a dual-functional fluorinated benzyl phosphonic acid (F-BPA) ligand that modulates the acidity and enhances the binding affinity between the phosphonate groups of F-BPA and the perovskite surface compared to BPA due to a significant redistribution of the electrostatic potential of the molecule induced by fluorination. The F-BPA treatment facilitates effective ligand exchange and obtains well-passivated CsPbI3 PeQDs with improved stability under thermal, light, and polar solvent stress. Red-emissive LEDs achieved a maximum external quantum efficiency of 24.0% with improved device stability (half-lifetime of 1,020 min at 100 cd m–2). This study demonstrates a dual-functional ligand strategy and opens a new pathway toward PeQDs for next-generation display technologies.

Abstract:

1D and 2D integrations provide significant promise for machine vision by enabling compact, power‐efficient optoelectronic devices. However, the potential of 1D materials in mixed‐dimensional structures for convolutional image processing remains largely unexplored. Here, high‐quality 1D‐Nb2Pd3Se8 is synthesized and integrated with 2D‐WSe2 to form self‐powered photodetectors, exhibiting gate‐tunable bi‐directional photoresponse for image processing. Utilizing the narrow band gap and favorable work function of 1D‐Nb2Pd3Se8, a type‐I junction and 1D van der Waals interface are established with transition metal dichalcogenides. The gate tunable built‐in electric field enables switching between n‐p and n‐n+ configurations, allowing the drift photocurrent direction to be reversed, achieving both negative and positive photocurrent. Furthermore, efficient conversion of high‐energy photons along one dimension enhances sensitivity at 375 nm. The device achieves a responsivity of 232 mA W−1, external quantum efficiency of 77% at 375 nm illumination, rapid response time of ~3 µs, detectivity of 6.35 × 1010 Jones, and broadband photodetection from ultraviolet to near‐infrared. The demonstrated gate‐controllable, bi‐directional photoresponse with linear power dependence in a 1D heterojunction offers a promising platform for in‐sensor convolutional processing with high integration and portability.