Enhanced aqueous stability and radiative-charge-transfer of CsPbBr3/Ag2S perovskite nanocrystal hybrids

Go beyond the limit: Rationally designed mixed-dimensional perovskite/semiconductor heterostructures and their applications

Halide perovskite heterojunctions rationally integrate the chemical and physical properties of multi-dimensional perovskites and judiciously chosen semiconductor materials, offering the promise of going beyond the limit of a single component. This emerging platform of materials innovation offers fresh opportunities to tune material properties, discover interesting phenomena, and enable novel applications. In this review, we first discuss the fundamentals of forming heterojunctions with perovskites and a wide range of semiconductors, and then we give an overview of the research progress of halide perovskite heterojunctions in terms of their optical, electrical, and mechanical properties, focusing on how the heterojunction tunes the energy band structure, electrical transport, and charge recombination behaviors. We further outline the progress of perovskite-based heterojunctions in optoelectronics. Finally, the challenges and future research directions for perovskite/semiconductor heterojunctions are discussed.

Coreactant-free and Near-Infrared Electrochemiluminescence Immunoassay with n-Type Au Nanocrystals as Luminophores

The electrochemiluminescence (ECL) bioassay is prominently carried out with the involvement of the coreactant. To remove the detrimental effects of the coreactant on the ECL of luminophores, herein, a promising ECL immunoassay strategy with biocompatible nanoparticles as the luminophore is proposed, which involves directly and electrochemically oxidizing the luminophore methionine-capped Au (Met@Au) nanocrystals (NCs) without the participation of any coreactant. Met@Au NCs are a kind of n-type nanoparticles, and they can be electrochemically injected with valence band (VB) holes around +0.80 and +1.10 V (vs Ag/AgCl). The electrochemically injected exogenous VB hole can recombine with the endogenous conduction band electron of Met@Au NCs and eventually bring out two coreactant-free and near-infrared ECL processes around 0.80 V (ECL-1) and 1.10 V (ECL-2). The intensity of coreactant-free ECL is primarily determined by the electrochemical oxidation-induced hole-injection process. ECL-2 is considerably stronger than ECL-1 and can be exploited for determining the carcinoembryonic antigen (CEA) in a sandwich immunoassay procedure with a linear range from 0.1 to 50 pg/mL as well as a limit of detection of 0.03 pg/mL (S/N = 3).

Coreactant-Free and Direct Electrochemiluminescence from Dual-Stabilizer-Capped InP/ZnS Nanocrystals: A New Route Involving n-Type Luminophore

Electrochemiluminescence (ECL) is conventionally generated in either an annihilation or a coreactant route, and the overwhelming majority of ECL research is conducted in the coreactant route via oxidizing or reducing the coexisting coreactant and luminophore. The coreacant-free ECL generated via merely oxidizing the luminophore would break through the ceiling of coreactant ECL via excluding the detrimental effects of exogenous coreactant and dissolved oxygen. Herein, by exploiting the rich-electron nature of n-type nanocrystals (NCs), coreacant-free ECL is achieved via merely oxidizing 3-mercaptopropionic acid (MPA) and mercaptosuccinic acid (MSA) capped InP/ZnS NCs, i.e., InP/ZnS_MPA-MSA. The electron-rich InP/ZnS_MPA-MSA can be electrochemically injected with holes via two oxidative processes at around +0.75 and +1.37 V (vs Ag/AgCl), respectively, and the exogenous hole can directly combine the conduction band (CB) electron of InP/ZnS_MPA-MSA, resulting in two coreactant-free ECL processes without employing any exogenous coreactant. The deprotonation process for the carboxyl group of the capping agents can provide a negatively charged surface to InP/ZnS_MPA-MSA and enhance the coreactant-free ECL. The hole-injecting process at +1.37 is much stronger than that at +0.75 V and eventually enables an ∼2000-fold enhanced ECL at +1.37 V than that at +0.75 V. The ECL at +1.37 V can be utilized for coreactant-free ECL immunoassay with prostate-specific antigen (PSA) as analyte, which exhibits an acceptable linear response from 5 pg·mL^-1 to 1 ng·mL^-1 with a limit of detection of 0.3 pg·mL^-1. The coreactant-free ECL route would provide an alternative to both annihilation and coreactant routes, simplify the ECL assay procedure and deepening the ECL mechanism investigations.

Modulating optical properties and interfacial electron transfer of CsPbBr3 perovskite nanocrystals via indium ion and chlorine ion co-doping

In this work, we demonstrated an in situ approach for doping CsPbBr₃ nanocrystals (NCs) with In³⁺ and Cl^- with a ligand-assisted precipitation method at room temperature. The In³⁺ and Cl^- co-doped NCs are characterized by the powder x-ray diffraction patterns, ultraviolet-visible, photoluminescence (PL) spectroscopy, time-resolved PL (TRPL), ultraviolet photoelectron spectroscopy, x-ray photoelectron spectroscopy, and transmission electron microscopy. Based on PL and TRPL results, the non-radiative nature of In³⁺-doping induced localized impurity states is revealed. Furthermore, the impact of In³⁺ and Cl^- doping on charge transfer (CT) from the NCs to molecular acceptors was investigated and the results indicate that the CT at the interface of NCs can be tuned and promoted by In³⁺ and Cl^- co-doping. This enhanced CT is attributed to the enlarged energy difference between relevant states of the molecular acceptor and the NCs by In³⁺ and Cl^- upon co-doping. This work provides insight into how to control interfacial CT in perovskite NCs, which is important for optoelectronic applications.

Encapsulation of lead halide perovskite nanocrystals (NCs) at the single-particle level: strategies and properties

Lead halide perovskite NCs (APbX₃, A = formamidinium (FA), methylammonium (MA) or Cs; X = Cl, Br, I or their mixture) have attracted unprecedented attention due to their excellent photophysical properties and wide application prospects. However, the inherent ionic structure of APbX₃ NCs makes them very sensitive to external conditions such as water and oxygen, resulting in poor stability. As a feasible strategy, encapsulation is considered to be effective in improving the stability. In this minireview, we focus on single-particle-level coating, which not only can improve the stability but also maintain the nano effect of the original NCs. This review summarizes the fundamental information on APbX₃ NCs and the necessity of single-particle-level coating. Subsequently, a variety of heterostructures at the single-particle level are introduced in detail. Then, their applications are summarized. Moreover, we discuss the challenges and prospects of the single-particle-level heterostructures based on APbX₃ NCs.

Recent Progress in Electrochemiluminescence of Halide Perovskites

Halide perovskites are a rapidly developing class of solution-processable semiconductors which, to date, have a huge impact across several scientific communities. The remarkable photophysical attributes of halide perovskites illustrate their considerable potential in the electrochemiluminescence (ECL) realm. Over the past 4 years, great progress has been achieved in using halide perovskites as ECL emitters. In this mini-review, the basic characteristics, synthetic approaches, and ECL mechanisms for halide perovskite emitters are first introduced. To the best of our knowledge, most of the reported ECL-active halide perovskites and their disclosed unique features are detailly summarized. Stabilization and interface manipulation strategies for desirable ECL performance are further highlighted. The preliminary halide perovskites-related ECL applications are finally discussed, and prospects are also anticipated.