Growth mechanistic insights into perovskite nanocrystals: dimensional growth

Concentration Dependent Modulation in Optoelectronic Traits of Self-Collated CsPbBr3 Perovskites

Self-collation of perovskite nanocrystals into superstructures of larger length scales has been growing in research interest due to their dramatically enhanced performance in various nano-devices, modulating their optical and electrical traits. Herein, the unique concentration-dependent self-assembly of phenethylamine (PEA)-capped CsPbBr3 (PCPB) perovskites spanning a size range of nano to micron level without structural phase alteration is infered. By optimizing various synthetic parameters like PEA amount, and solvents, the self-coalescence in PCPB crystal growth is controlled. Furthermore, the highest-concentrated PCPB (C5) has improved the charge transfer (CT) efficiency to 1,4-Napthoquinone (NPQ), corroborated with stronger binding between C5 and NPQ, compared to the lowest-concentrated PCPB (C1). Incorporating NPQ into such concentration-dependent PCPB enhances their local conductance unveiling the CT-induced current rise, while the detrimental insulating property of PEA molecules reduces the conductance in C5 compared to C1. These outcomes offer a foundation for tailoring the properties of self-assembled perovskites for optoelectronic devices and energy conversion technologies.

Ni doping in CsPbCl3 nanocrystals: the key to enhanced photoluminescence

This study presents a generic method to selectively enhance radiative pathways over non-radiative states by leveraging vibrational coupling between the host lattice and mid-gap states of doped transition metal ions. While previously demonstrated with Mn, this work successfully incorporates Ni2+ ions into CsPbCl3 perovskite nanocrystals (NCs), showcasing the method's versatility and tunability for radiative decay rates. Structural analyses confirm Ni2+ integration, while temperature-dependent photoluminescence studies reveal that Ni-induced shallow trap states enable vibrational coupling, facilitating charge carrier back-transfer to excitonic states. At 2% doping, this mechanism optimally enhances radiative recombination, achieving room-temperature vibrationally assisted delayed fluorescence (VADF). Förster resonance energy transfer (FRET) experiments further validate the improved radiative efficiency. This work establishes transition metal doping as a transformative and selective strategy for tuning optical properties, paving the way for advancements in energy-efficient technologies such as light-emitting diodes, lasers, and photovoltaics.

Delayed Fluorescence in Dual-Doped Perovskite Nanocrystals: Insight into the Role of Dopants

This study investigates the photophysical behaviour of Mn/Fe and Mn/Sn co-doped CsPbCl3 perovskite nanocrystals (NCs) to explore carrier dynamics and dopant interactions. Using gated photoluminescence (PL) and temperature-dependent measurements, we elucidate the impact of dopant chemistry on exciton behaviour, focusing on vibrationally assisted delayed fluorescence (VADF) and energy transfer mechanisms. The efficiency of VADF is influenced by factors such as the bandgap, temperature, quantum confinement, and host composition. In Mn/Fe co-doped NCs, Fe-induced trap states introduce additional radiative pathways, resulting in a unique emission around 515 nm. In contrast, in Mn/Sn co-doped NCs, Sn captures photoexcited carriers, preventing the VADF process and leading to non-radiative decay. The findings provide key insights into dopant-dopant interactions and the mechanisms governing carrier transfer, enhancing our understanding of these materials for future optoelectronic applications.

Exploring Nanoscale Perovskite Materials for Next-Generation Photodetectors: A Comprehensive Review and Future Directions

The rapid advancement of nanotechnology has sparked much interest in applying nanoscale perovskite materials for photodetection applications. These materials are promising candidates for next-generation photodetectors (PDs) due to their unique optoelectronic properties and flexible synthesis routes. This review explores the approaches used in the development and use of optoelectronic devices made of different nanoscale perovskite architectures, including quantum dots, nanosheets, nanorods, nanowires, and nanocrystals. Through a thorough analysis of recent literature, the review also addresses common issues like the mechanisms underlying the degradation of perovskite PDs and offers perspectives on potential solutions to improve stability and scalability that impede widespread implementation. In addition, it highlights that photodetection encompasses the detection of light fields in dimensions other than light intensity and suggests potential avenues for future research to overcome these obstacles and fully realize the potential of nanoscale perovskite materials in state-of-the-art photodetection systems. This review provides a comprehensive overview of nanoscale perovskite PDs and guides future research efforts towards improved performance and wider applicability, making it a valuable resource for researchers.

In Situ Real-Time Observation of Formation and Self-Assembly of Perovskite Nanocrystals at High Temperature

All-inorganic cesium lead halide perovskite nanocrystals (NCs) have received much attention due to their outstanding optical and electronic properties, but the underlying growth mechanism remains elusive due to their rapid formation process. Here, we report an in situ real-time study of the growth of Cs4PbBr6 NCs under practical synthesis conditions in a custom-made reactor. Through the synchrotron-based small-angle X-ray scattering technique, we find that the formation of Cs4PbBr6 NCs is accomplished in three steps: the fast nucleation process accompanied by self-focusing growth, the subsequent diffusion-limited Ostwald ripening, and the self-assembly of NCs into the face-centered cubic (fcc) superlattices at high temperature and the termination of growth. The simultaneously collected wide-angle X-ray scattering signals further corroborate the three-step growth model. The influence of superlattice formation is also elucidated, which improves the uniformity of the final NCs.

Experimental Determination of the Molar Absorption Coefficient of Cesium Lead Halide Perovskite Quantum Dots

Lead halide perovskite (CsPbX₃, where X = Cl, Br, or I) quantum dots (QDs), with tunable optical and electronic properties, have attracted attention because of their promising applications in solar cells and next-generation optoelectronic devices. Hence, it is crucial to investigate in detail the fundamental size-dependent properties of these perovskite QDs to obtain high-quality nanocrystals for practical use. We propose a direct method for determining the concentration of solution-processed CsPbX₃ QDs by means of spectrophotometry, in which the molar absorption coefficient (ε) is obtained using absorption and the Beer-Lambert law. By tuning the size of CsPbX₃ QDs, we obtain their corresponding ε leading to a calibration curve for calculating the nanocrystal concentrations. The ε at the band edge for CsPbX₃ (X = Cl, Br, or I) nanocrystals was found to be strongly dependent on the bandgap of the nanocrystals. We also obtained a reliable size dependence of the bandgap calibration curves to estimate the size of QDs from the absorption spectra.

Photoluminescence Quenching in CsPbCl3 upon Fe Doping: Colloidal Synthesis, Structural and Optical Properties

Doped perovskite lead halide nanocrystals (PHNCs) are promising materials for various optoelectronic applications, but the major challenge faced by the researchers is the inability to dope foreign elements into perovskite lattice because of the strong lead-halide bond energies. In this work, we have used Fe as a dopant in CsPbCl₃ to explore different doping techniques based on the colloidal synthesis of PHNCs to investigate the advantages and disadvantages of different techniques. We are able to dope a relatively higher amount of Fe (∼10%) than reported and observe clear optical signatures when the precursor does not have pre-existing Pb-Cl bonds. We prove that there are two competing processes inside a doped PHNC - one is the effect of dopant energy levels, and the other is surface passivation by halide ions. Using the most optimal synthesis strategy, we show that although Fe does act as a luminescence quencher in perovskite similar to II-VI quantum dots (QDs), the quenching requires much more Fe compared to trace amounts of Fe required in traditional QDs. Our work will assist in giving an overall comparative idea of doping and finding the most optimized strategy and help identify the underlying physical processes in perovskite based QDs.