Transition Layer Assisted Synthesis of Defect Free Amine-Phosphine Based InP QDs.

Environmentally friendly InP-based quantum dots (QDs) are promising for light-emitting diodes (LEDs) and display applications. So far, the synthesis of highly emitting InP-based QDs via safe and economically viable amine-phosphine remains a challenge. Herein, we report the synthesis of amine-phosphine based InP/ZnSe/ZnS QDs by introducing an alloyed oxidation-free In-ZnSe transition layer (TL) at the core-shell interface. The TL not only has the essential function of preventing oxidation of the core and relieving interfacial strain but also results in oriented epitaxial growth of shell. The alloyed TL significantly mitigates the nonradiative recombination at core-shell interfacial trap states, thereby boosting the photoluminescence (PL) efficiency of the QDs up to 98%. Also, the Auger recombination is suppressed, extending the biexciton lifetime from 60 to 100 ps. The electroluminescence device based on the InP-based QDs shows a high external quantum efficiency over 10%, further demonstrating high quality QDs synthesized by this process.

Tailoring Auger Recombination Dynamics in CsPbI3 Perovskite Nanocrystals via Transition Metal Doping.

Auger recombination is a pivotal process for semiconductor nanocrystals (NCs), significantly affecting charge carrier generation and collection in optoelectronic devices. This process depends mainly on the NCs' electronic structures. In our study, we investigated Auger recombination dynamics in manganese (Mn2+)-doped CsPbI3 NCs using transient absorption (TA) spectroscopy combined with theoretical and experimental structural characterization. Our results show that Mn2+ doping accelerates Auger recombination, reducing the biexciton lifetime from 146 to 74 ps with increasing Mn doping concentration up to 10%. This accelerated Auger recombination in Mn-doped NCs is attributed to increased band edge wave function overlap of excitons and a larger density of final states of Auger recombination due to Mn orbital involvement. Moreover, Mn doping reduces the dielectric screening of the excitons, which also contributes to the accelerated Auger recombination. Our study demonstrates the potential of element doping to regulate Auger recombination rates by modifying the materials' electronic structure.

N-Doping Donor-Dilute Semitransparent Organic Solar Cells to Weaken Donor: Acceptor Miscibility and Consolidate Donor-Phase Continuity.

Lightweight and semi-transparent organic solar cells (ST-OSCs) offer bright promise for applications such as building integrated photovoltaics. Diluting donor content in bulk-heterojunction active layers to allow greater visible light transmittance (AVT) effectively enhances device transparency, yet the ineluctable compromise of the donor-phase continuity is challenging for efficient charge transport. Herein, a trace amount of n-type N-DMBI dopant is incorporated, which facilitates the donor:acceptor (D:A) de-mixing by strengthening both acceptor polarity and D/A crystallization. With the diminution of component inter-mixing, the limited number of donors increasingly self-aggregate to establish the more continuous phases. For the benchmark PM6:Y6-based ST-OSCs, when the donor content is reduced from regular 45 to optimal 30 wt.%, the device AVT is remarkably raised by more than a quarter, accompanied by a marginal drop in power conversion efficiency from 13.89% to 13.03%. This study reveals that by decreasing the donor content to <30 wt%, acceptor excitons induced by Förster resonance energy transfer are prone to severe radiative recombination. This is nonetheless mitigated by dopant inclusion within the acceptor phase by providing extra energy offset and prolonging charge transfer state lifetime to assist exciton dissociation.

Constructing ZnTe Spherical Quantum Well for Efficient Light Emission.

ZnTe colloidal semiconductor nanocrystals (NCs) have shown promise for light-emitting diodes (LEDs) and displays, because they are free from toxic heavy metals (Cd). However, so far, their low photoluminescence (PL) efficiency (∼30%) has hindered their applications. Herein, we devised a novel structure of ZnTe NCs with the configuration of ZnSe (core)/ZnTe (spherical quantum well, SQW)/ZnSe (shell). The inner layer ZnTe was grown at the surface of ZnSe core with avoiding using highly active and high-risk Zn sources. Due to the formation of coherently strained heterostructure which reduced the lattice mismatch, and the thermodynamic growth of ZnTe, the surface or interface defects were suppressed. A high PL efficiency of >60% was obtained for the green light-emitting ZnSe/ZnTe/ZnSe SQWs after ZnS outer layer passivation, which is the highest value for colloidal ZnTe-based NCs. This work paves the way for the development of novel semiconductor NCs for luminescent and display applications.

High-Quality Solution-Processed Quasi-2D Perovskite for Low-Threshold Lasers.

Spin-coated quasi-two-dimensional halide perovskite films, which exhibit superior optoelectronic properties and environmental stability, have recently been extensively studied for lasers. Crystallinity is of great importance for the laser performance. Although some parameters related to the spin-coating process have been studied, the in-depth understanding and effective control of the acceleration rate on two-dimensional perovskite crystallization during spin-coating are still unknown. Here we investigate the effect of solvent evaporation on the microstructure of the final perovskite films during the spin-coating process. The crystallization quality of the film can be significantly improved by controlling solvent evaporation. As a result, the prepared quasi-2D perovskite film exhibits a stimulated emission threshold (pump: 343 nm, 6 kHz, 290 fs) of 550 nm as low as 16.2 µJ/cm2. Transient absorption characterization shows that the radiative biexciton recombination time is reduced from 738.5 to 438.3 ps, benefiting from the improved crystallinity. The faster biexciton recombination significantly enhanced the photoluminescence efficiency, which is critical for population inversion. This work could contribute to the development of low-threshold lasers.

Nonadiabatic Charge Transfer within Photoexcited Nickel Porphyrins.

Metalloporphyrins with open d-shell ions can drive biochemical energy cycles. However, their utilization in photoconversion is hampered by rapid deactivation. Mapping the relaxation pathways is essential for elaborating strategies that can favorably alter the charge dynamics through chemical design and photoexcitation conditions. Here, we combine transient optical absorption spectroscopy and transient X-ray emission spectroscopy with femtosecond resolution to probe directly the coupled electronic and spin dynamics within a photoexcited nickel porphyrin in solution. Measurements and calculations reveal that a state with charge-transfer character mediates the formation of the thermalized excited state, thereby advancing the description of the photocycle for this important representative molecule. More generally, establishing that intramolecular charge-transfer steps play a role in the photoinduced dynamics of metalloporphyrins with open d-shell sets a conceptual ground for their development as building blocks capable of boosting nonadiabatic photoconversion in functional architectures through "hot" charge transfer down to the attosecond time scale.