Multiheterojunction Phototransistors Based on Graphene–PbSe Quantum Dot Hybrids

Graphene-semiconductor quantum dot (QD) hybrid field effect phototransistors (FEpTs) have attracted much interest due to their ultrahigh gain and responsivity in photo detection. However, most reported results are based on single-layer heterojunction, and the multiheterojunction FEpTs are often ignored. Here, we design two typical multiheterojunction FEpTs based on graphene–PbSe quantum dot (QD) hybrids, including QD at the bottom layer (QD-bottom) and graphene at the bottom layer (G-bottom) FEpTs. Through a comparative study, G-bottom FEpTs showed a multisaturation behavior due to the multigraphene layer effect, which was absent in the QD-bottom FEpTs. The mobilities for electrons and holes were μ_E = 147 cm² V^–1 s^–1 and μ_E = 137 cm² V^–1 s^–1 in the G-bottom FEpTs and μ_E = 14 cm² V^–1 s^–1 and μ_E = 59 cm² V^–1 s^–1 in the QD-bottom FEpTs. Higher responsivity (∼10⁶ A W^–1) and faster response rate were both achieved by the G-bottom FEpTs. All of the advantages in G-bottom FEpTs were attributed to the back-gate effect. Therefore, high performance is expected in those FEpTs whose heterojunctions are designed to be close to the back-gate

Ambipolar Quantum-Dot-Based Low-Voltage Nonvolatile Memory with Double Floating Gates

Considerable research efforts have been devoted to promoting memory performance, especially the memory window and retention time. In this work, we develop an innovative field-effect-transistor memory with graphene oxide (GO)/gold nanoparticles (Au NPs) as double floating gates (DFG) and PbS quantum dots (QDs) as the semiconductor layer. QDs can provide both electrons and holes in the channel, which offers a chance for the floating gates to trap both of them to achieve bidirectional threshold voltage shifts after programming and erasing operations. Due to the DFG structure covering the GO sheets on the Au NP monolayer, the enhanced memory window (∼2.72 V at a programming/erasing voltage of ±10 V) can be attributed to more charge carriers being trapped in the floating gates. More importantly, because of the different energy levels between GO and Au NPs, the DFG construction brings about an energy barrier that prevents the trapped charges from leaking back to the channel, so that the retention capability is significantly improved. The outstanding memory performance will give the QD-based DFG memory great potential to have its own place in the flash memory market

PbS-Decorated WS₂ Phototransistors with Fast Response

Tungsten disulfide (WS₂), as a typical metal dichalcogenides (TMDs), has aroused keen research interests in photodetection. Here, field effect phototransistors (FE_pTs) based on heterojunction between monolayer WS₂ and PbS colloidal quantum dots are demonstrated to show high photoresponsivity (up to ∼14 A/W), wide electric bandwidth (∼396 Hz), and excellent stability. Meanwhile, the devices exhibit fast photoresponse times of ∼153 μs (rise time) and ∼226 μs (fall time) due to the assistance of heterojunction on the transfer of photoexcitons. Therefore, excellent device performances strongly underscore monolayer WS₂–PbS quantum dot as a promising material for future photoelectronic applications

All-Photon Bipolar Reversible Modulation Artificial Synapse for Color Perception and Mitigation of Glare Phenomenon

The convergence of computation and storage through artificial synapses is a vibrant area of research, with notable attention directed toward photonic artificial synapses, particularly in emulating human visual perception and memory. However, many of these solutions necessitate both optical and electrical signals for bidirectional modulation. In this work, we report an optically responsive memristor (with a configuration of Ag:AgI/MA0.4FA0.6PbI3/Ag:AgI) that achieves bidirectional switching of resistive states utilizing 450 and 650 nm light at an ultralow readout voltage of 0.001 V. The maximum high-to-low resistive switching ratio can attain an impressive value of 74,459 at the readout voltage of 0.01 V, enabling comprehensive photonic bipolar modulation. The device presents artificial visual synapse (AVS) features in terms of short-term plasticity (STP)/long-term plasticity (LTP) to pulsed light in the range 300–700 nm. Under 450 nm blue light, an abrupt shift from low to high resistance can be observed, resembling the effect of glare. Intriguingly, the introduction of 650 nm red light can expedite recovery following blue light exposure. These attributes underscore the potential of the device for tasks encompassing color recognition, memory functions, and adaptation, suggesting promising prospects within artificial visual neural networks for ultraviolet and visible light sensing, transmission, and memory applications

Less-Lead Control toward Highly Efficient Formamidinium-Based Perovskite Light-Emitting Diodes

A formamidinium (FA)-based perovskite is an ideal option for the potential efficient light-emitting diode (LED) in view of its high tolerance factor closer to 1. In this work, FA cation-based perovskite nanocrystals FA_0.8Cs_0.2Pb_<i>x</i>Br₃ (<i>x</i> = 1.0, 0.8, 0.7, and 0.6) are fabricated with stoichiometric modification. The adoption of less-lead precursor is confirmed to be a feasible and effective approach in inhibiting nonradiative recombination by diminishing the presence of uncoordinated metallic Pb atoms. Note that the subsequent devices require the optimized lead ratio for an optimum behavior, a clear influence of Pb ratio on a perovskite LED has been established. No surprisingly, the less-lead perovskites exert positive roles on the perovskite LED performance, not only in terms of efficiency but also in stability. With an optimized composition FA_0.8Cs_0.2Pb_0.7Br₃, the perovskite LED displays the prominent performance with a current efficiency of 28.61 cd A^–1, about 11-fold improvement than the previous best record of pure FA-based perovskite. Additionally, the perovskite device degradation can be mitigated under operating conditions by properly altering precursor stoichiometry, which can be attributed to the hydrogen reaction under moisture-induced ambient. The stoichiometric optimization of the metal Pb in the perovskite is an important strategy on the road to the further development of perovskite LEDs

Broadband Phototransistor Based on CH₃NH₃PbI₃ Perovskite and PbSe Quantum Dot Heterojunction

Organic lead halide perovskites have received a huge amount of interest since emergence, because of tremendous potential applications in optoelectronic devices. Here field effect phototransistors (FE_pTs) based on CH₃NH₃PbI₃ perovskite/PbSe colloidal quantum dot heterostructure are demonstrated. The high light absorption and optoelectric conversion efficiency, due to the combination of perovskite and quantum dots, maintain the responsivities in a high level, especially at 460 nm up to 1.2 A/W. The phototransistor exhibits bipolar behaviors, and the carrier mobilities are determined to be 0.147 cm²V^–1s^–1 for holes and 0.16 cm²V^–1s^–1 for electrons. The device has a wide spectral response spectrum ranging from 300 to 1500 nm. A short photoresponse time is less than 3 ms due to the assistance of heterojunction on the transfer of photoexcitons. The excellent performances presented in the device especially emphasize the CH₃NH₃PbI₃ perovskite–PbSe quantum dot as a promising material for future photoelectronic applications

Black Phosphorus Quantum Dot Induced Oxidative Stress and Toxicity in Living Cells and Mice

Black phosphorus (BP), as an emerging successor to layered two-dimensional materials, has attracted extensive interest in cancer therapy. Toxicological studies on BP are of great importance for potential biomedical applications, yet not systemically explored. Herein, toxicity and oxidative stress of BP quantum dots (BPQDs) at cellular, tissue, and whole-body levels are evaluated by performing the systemic <i>in vivo</i> and <i>in vitro</i> experiments. <i>In vitro</i> investigations show that BPQDs at high concentration (200 μg/mL) exhibit significant apoptotic effects on HeLa cells. <i>In vivo</i> investigations indicate that oxidative stress, including lipid peroxidation, reduction of catalase activity, DNA breaks, and bone marrow nucleated cells (BMNC) damage, can be induced by BPQDs transiently but recovered gradually to healthy levels. No apparent pathological damages are observed in all organs, especially in the spleen and kidneys, during the 30-day period. This work clearly shows that BPQDs can cause acute toxicities by oxidative stress responses, but the inflammatory reactions can be recovered gradually with time for up to 30 days. Thus, BPQDs do not give rise to long-term appreciable toxicological responses