Stable and strong emission CsPbBr3 quantum dots by surface engineering for high performance optoelectronic films. ACS Applied Materials and Interfaces .

Emerging technologies such as autonomous driving and augmented reality rely on light detection and ranging (LiDAR based on time of flight (ToF). [3] This requires sensitive and ultrafast photodetection of infrared light with nanoseconds' resolution. [4] Today, this is achieved in the near-infrared (NIR) using indirect bandgap silicon detectors-limited by silicon's low absorption coefficient-and, at longer wavelengths, using epitaxially grown semiconductors such as III-Vs and Hg 1−x Cd x Te. [5,6] Colloidal quantum dots (CQDs) are of interest given by their low-temperature solution processing, which allows them to be integrated with silicon electronic readout and signal-processing circuitry. [7][8][9][10] Their bandgap is size-tuned over a wide range of wavelengths. PbS, for example, has a widely programmable absorption onset covering the visible and shortwavelength infrared (SWIR); [11,12] however, its high permittivity, stemming from its ionic character-ε r = 180 for bulk PbS [13] slows charge extraction both for bulk [14] and CQD photodiodes [15] due to screening and capacitance effects.Colloidal quantum dots (CQDs) are promising materials for infrared (IR) light detection due to their tunable bandgap and their solution processing; however, to date, the time response of CQD IR photodiodes is inferior to that provided by Si and InGaAs. It is reasoned that the high permittivity of II-VI CQDs leads to slow charge extraction due to screening and capacitance, whereas III-Vs-if their surface chemistry can be mastered-offer a low permittivity and thus increase potential for high-speed operation. In initial studies, it is found that the covalent character in indium arsenide (InAs) leads to imbalanced charge transport, the result of unpassivated surfaces, and uncontrolled heavy doping. Surface management using amphoteric ligand coordination is reported, and it is found that the approach addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine high mobility (0.04 cm 2 V −1 s −1 ) with a 4× reduction in permittivity compared to PbS CQDs. The resulting photodiodes achieve a response time faster than 2 nsthe fastest photodiode among previously reported CQD photodiodes-combined with an external quantum efficiency (EQE) of 30% at 940 nm.

Colloidal InP quantum dots (QDs) have been considered as one of the most promising candidates for display and biolabeling applications because they are intrinsically toxicity-free and exhibit high photoluminescence. On account of the uncontrollable nucleation and growth during the synthesis of InP, obtaining high-quality blue-emitting InP QDs with uniform size distribution remains a challenge. Herein, we employ a novel synthetic approach for producing blue-emitting InP/ZnS core/shell QDs with the assistance of copper cations. The studies reveal that the copper ions could combine with phosphorus precursor to form hexagonal Cu3–x P nanocrystals, which competed with the nucleation process of InP QDs, resulting in the smaller sized InP QDs with blue photoluminescence emission. After the passivation of InP QDs with the ZnS shell, the synthesized InP/ZnS core/shell QDs present bright blue emission (∼425 nm) with a photoluminescence quantum yield of ∼25%, which is the shortest wavelength emission for InP QDs to date. This research provides a new way to synthesize ultrasmall semiconductor nanocrystals.

Inorganic halide CsPbI3 perovskite colloidal quantum dots (QDs) possess remarkable potential in photovoltaics and light-emitting devices owing to their excellent optoelectronic performance. However, the poor stability of CsPbI3 limits its practical applications. The ionic radius of SCN − (217 pm) is comparable to that of I − (220 pm), whereas it is marginally larger than that of Br − (196 pm), which increases the Goldschmidt tolerance factor of CsPbI3 and improves its structural stability. Recent studies have shown that adding SCN − in the precursor solution can enhance the crystallinity and moisture resistance of perovskite film solar cells; however, the photoelectric properties of the material post SCN − doping remain unconfirmed. To date, it has not been clarified whether SCN − doping occurs solely on the perovskite surfaces, or if it advances within their structures. In this study, we synthesized inorganic perovskite CsPbI3 QDs via a hot-injection method. Pb(SCN)2 was added to the precursor for obtaining SCN − -doped CsPbI3 (SCN-CsPbI3). X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) were conducted to demonstrate the doping of SCN − ions within the perovskite structures. XRD and TEM indicated a lattice expansion within the perovskite, stemming from the large steric hindrance of the SCN − ions, along with an enhancement in the lattice stability due to the strong bonding forces between SCN − and Pb 2+ . Through XPS, we confirmed the existence of the S peak, and further affirmed that the bonding energy between Pb 2+ and SCN − was stronger than that between Pb 2+ and I − . The space charge limited current and time-resolved photoluminescence results demonstrated a decrease in the trap density of the perovskite after being doped with SCN − ; therefore, the doping process mitigated the defects of QDs, thereby increasing their optical performance, and further enhanced the bonding energy of Pb-X and crystal quality of QDs, thereby improving the stability of perovskite structure. Therefore, the photoluminescence quantum yield (PLQY) of the SCN-CsPbI3 QDs exceeded 90%, which was significantly higher than that of pristine QDs (68%). The high PLQY indicates low trap density of QDs, which is attributed to a decrease in the defects. Furthermore, the SCN-CsPbI3 QDs exhibited remarkable water-resistance performance, while maintaining 85% of their initial photoluminescence intensity under water for 4 h, whereas the undoped samples suffered complete fluorescence loss due to the phase transformations caused by water molecules. The SCN-CsPbI3 QDs photodetector measurements demonstrated a broad band range of 400-700 nm, along with a responsivity of 90 mA•W −1 and detectivity exceeding 10 11 Jones, which were considerably higher than the corresponding values of the control device (responsivity: 60 mA•W −1 and detectivity: 10 10 Jones). Finally, extending the doping of SCN − into CsPbCl3 and CsPbBr3 QDs further enhanced their optical properties on a significant scale.

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