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Atomic-scale examination of lead halide perovskites is currently a subject of growing interest for applications in the optimization of perovskite-based photovoltaic and optoelectronic devices. While transmission electron microscopy (TEM) is a powerful tool to characterize these electron-sensitive materials at the atomic scale, it induces structural and chemical modifications along with other undesirable artifacts. Here, we investigate the phase stability of nominally Cu-doped CsPbI3 nanocrystals, with enhanced structural stability as compared to their pristine counterparts, against electron irradiation using high-resolution TEM at ambient conditions. Our findings reveal a significant transformation from the cubic to the orthorhombic phase at a dose of ∼3 × 103 e–/Å2. Analysis of the beam energy deposited per unit cell, along with the evolution of lattice energy with varying cell dimensions, as obtained from density functional theory, provides valuable insights into the mechanisms governing the beam-induced phase decomposition process, corroborated by the phonon dispersion of the system, which is not yet reported. At a critical dose of ∼1.68 × 106 e–/Å2, the lattice undergoes complete and irreversible degradation. Thus, our study demonstrates real-time in situ beam-induced phase decomposition in Cu-doped CsPbI3 for the first time, with an estimation of the electron dose limits below which beam-induced alterations are minimal, allowing accurate imaging and analysis of perovskites. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon dots (NCDs), exhibiting strong yellow emission in aqueous solution and solid matrices, have been utilized for fabricating heterostructure white electroluminescence devices. These devices consist of nitrogen-doped carbon dots as an emissive layer sandwiched between an organic hole transport layer (PEDOT:PSS) and an array of rutile TiO2 nanorods, acting as an electron transport layer. Under an applied forward bias of 5 V, the device exhibits broadband electroluminescence covering the wavelength range of 390–900 nm, resulting in pure white light emission characteristics at room temperature. The result demonstrates the successful fabrication of all solution-processed, low-cost, eco-friendly NCDs-based LEDs with CIE (Commission Internationale d'Éclairage) coordinate of (0.31, 0.34) and color rendering index (CRI) > 90, which are close to ideal white light emission characteristics. The device functionalities are achieved based on defect-related NIR emission from TiO2 nanorods array and visible emission from nitrogen-doped carbon dots. This result paves a new opportunity to develop low-cost, solution-processed nitrogen-doped carbon dots based on warm White light emitting diodes with high CRI for large-area display and lighting applications. [ABSTRACT FROM AUTHOR]

Hot carrier extraction is crucial for efficient solar energy harvesting, and lead halide perovskite nanocrystals (NCs) are potential candidates for photovoltaic and light-emitting applications. Therefore, swift extraction of hot carriers is an immediate requirement to improve the energy conversion efficiency, which need longer thermalization time. To address this issue, we synthesized nominally Cu-doped CsPbI3 NCs with enhanced structural and optical characteristics compared to undoped CsPbI3 NCs. We investigated the hot carrier dynamics in both the NCs at different fluences using ultrafast transient absorption spectroscopy. Interestingly, we observed very fast thermalization at higher fluences that indicated breaking of the phonon bottleneck. On the contrary, doped NCs preserved the effects and decayed over a longer period of time possibly due to increase in size and introduction of shallow trap states of Cu 3d and Cu 4s electrons in the conduction band, as computed using density functional theory. Notably, as the carrier–carrier interaction increased, we observed a dominating bandgap renormalization in the doped system compared to the undoped system. Overall, our studies improve the understanding of Cu doping in enhancing the hot carrier dynamics in perovskites and open possibilities for further investigation in the quantum phenomenon of these materials. [ABSTRACT FROM AUTHOR]

Although α‐CsPbI3 is regarded as an attractive optical luminophore, it is readily degraded to the optically inactive δ‐phase under ambient conditions. Here, we present a simple approach to revive degraded ("optically sick") α‐CsPbI3 through "medication" with thiol‐containing ligands. The effect of different types of thiols is systematically studied through optical spectroscopy. The structural reconstruction of degraded α‐CsPbI3 nanocrystals to cubic crystals in the presence of thiol‐containing ligands is visualized through high‐resolution transmission electron microscopy and supported by X‐ray diffraction analysis. We found that 1‐dodecanethiol (DSH) effectively revives degraded CsPbI3 and results in high immunity towards moisture and oxygen, hitherto unreported. DSH facilitates the passivation of surface defects and etching of degraded Cs4PbI6 phase, thus reverting them back to the cubic CsPbI3 phase, leading to enhanced PL and environmental stability. [ABSTRACT FROM AUTHOR]

Among the lead halide perovskite (LHP) family, CsPbI 3 is known to be significantly vulnerable to moisture, which hinders its use in real device applications. It is reported that chalcogen-based ligands can better stabilize CsPbI 3 and revive nanocrystals (NCs). Here, diphenyl diselenide (DPhDSe) ligand is used to revive the degraded CsPbI 3 NCs through a post-synthetic treatment of adding a small amount of DPhDSe in the degraded NC dispersion. DPhDSe in the dispersion formed nanofibrillar crystals at a low temperature through the π-π stacking of the phenyl ring. The nanofibrils played as a template on which the NCs self-assembled and they are attached side-by-side to form microfibers. The microfiber powder containing the NCs is optically stable at ambient conditions and morphologically self-healable by mild thermal annealing due to the dynamic Se─Se bond. The mechanism of the structural changes, optical transitions, and chemical changes has been systematically characterized through electron microscopy, diffraction, spectroscopy, and elemental analysis., (© 2024 Wiley‐VCH GmbH.)

Nitrogen-doped carbon dots (NCDs), exhibiting strong yellow emission in aqueous solution and solid matrices, have been utilized for fabricating heterostructure white electroluminescence devices. These devices consist of nitrogen-doped carbon dots as an emissive layer sandwiched between an organic hole transport layer (PEDOT:PSS) and an array of rutile TiO 2 nanorods, acting as an electron transport layer. Under an applied forward bias of 5 V, the device exhibits broadband electroluminescence covering the wavelength range of 390-900 nm, resulting in pure white light emission characteristics at room temperature. The result demonstrates the successful fabrication of all solution-processed, low-cost, eco-friendly NCDs-based LEDs with CIE (Commission Internationale d'Éclairage) coordinate of (0.31, 0.34) and color rendering index (CRI) > 90, which are close to ideal white light emission characteristics. The device functionalities are achieved based on defect-related NIR emission from TiO 2 nanorods array and visible emission from nitrogen-doped carbon dots. This result paves a new opportunity to develop low-cost, solution-processed nitrogen-doped carbon dots based on warm White light emitting diodes with high CRI for large-area display and lighting applications., (© 2023 IOP Publishing Ltd.)

Although α-CsPbI 3 is regarded as an attractive optical luminophore, it is readily degraded to the optically inactive δ-phase under ambient conditions. Here, we present a simple approach to revive degraded ("optically sick") α-CsPbI 3 through "medication" with thiol-containing ligands. The effect of different types of thiols is systematically studied through optical spectroscopy. The structural reconstruction of degraded α-CsPbI 3 nanocrystals to cubic crystals in the presence of thiol-containing ligands is visualized through high-resolution transmission electron microscopy and supported by X-ray diffraction analysis. We found that 1-dodecanethiol (DSH) effectively revives degraded CsPbI 3 and results in high immunity towards moisture and oxygen, hitherto unreported. DSH facilitates the passivation of surface defects and etching of degraded Cs 4 PbI 6 phase, thus reverting them back to the cubic CsPbI 3 phase, leading to enhanced PL and environmental stability., (© 2023 Wiley-VCH GmbH.)