Black Phosphorus Quantum Dots

Abstract

As a unique two-dimensional nanomaterial, layered black phosphorus (BP) nanosheets have shown promising applications in electronics. Although mechanical exfoliation was successfully used to prepare BP nanosheets, it is still a challenge to produce novel BP nanostructures in high yield. A facile top-down approach for preparation of black phosphorus quantum dots (BPQDs) in solution is presented. The obtained BPQDs have a lateral size of 4.9 AE 1.6 nm and thickness of 1.9 AE 0.9 nm (ca. 4 AE 2 layers). As a proof-ofconcept application, by using BPQDs mixed with polyvinylpyrrolidone as the active layer, a flexible memory device was successfully fabricated that exhibits a nonvolatile rewritable memory effect with a high ON/OFF current ratio and good stability.Two-dimensional (2D) layered materials, such as graphene and transition-metal dichalcogenides (TMDs), have emerged as a class of promising nanomaterials in both fundament studies and potential applications owing to their intriguing properties. [1] Besides the 2D layered structure, ultra-small quantum dot (QD), as another form of nanomaterials, exhibits unique electronic and optical properties owing to the quantum confinement and edge effects. [2] For example, graphene and MoS 2 QDs have been successfully prepared and widely used in photovoltaic devices, [3] opto-electronics, [4] and biological analysis. [5] Inspired by the unique 2D feature of graphene and TMDs, considerable efforts have been devoted to the exploration of new members in the 2D family. As a typical example, black phosphorus (BP), a conceptually new layered material, has triggered a recent resurgence of interest owing to its unique structure as well as fascinating optical and electronic properties. [6] As bulk BP consists of puckered layers stacked together by weak van der Waals interactions, the mechanical exfoliation method has been successfully used to prepare single-and few-layer BP nanosheets. [6a, 7] Importantly, BP has a layerdependent bandgap, which can be tuned from 0.3 to 2 eV as its thickness decreased from bulk to monolayer. [6c, 8] The appealing tunable bandgap of BP holds great promise in bridging the space between zero-gap graphene [1a] and large-gap TMDs (1-2 eV). [1f] Moreover, it has been theoretically predicted that the bandgaps of its monolayer (phosphorene) and nanoribbon are highly sensitive to the plane strain and edge structures. [9] Based on its intriguing properties, BP nanosheets have been used in field-effect transistors (FETs), [6a,d] and theoretically predicted for thin film solar-cell [10] and gas sensing [11] applications. Despite the recent progress in mechanically exfoliated BP nanosheets, it is still a challenge to prepare new BP nanostructures in high yield, especially through solutionbased approaches.Herein, for the first time, we report a facile solution-based method for the preparation of black phosphorus quantum dots (BPQDs) from the bulk BP crystal. The as-synthesized BPQDs with average size of 4.9 AE 1.6 nm and thickness of 1.9 AE 0.9 nm (that is,...

Black phosphorus as a new lubricant

“…Owing to the aforementioned attractive properties of BP, the exploration of relevant applications has made rapid progress in the fields of electronics, field-effect transistors [58,59], sensors [60], energy storage [60−62], batteries [63], photocatalysis [64,65], and optoelectronics [66], and other applications.…”

Black Phosphorus Quantum Dots Used for Boosting Light Harvesting in Organic Photovoltaics

“…Zuschriften cated with the addition of three different BPQDs under the same preparation conditions. [26] Figure 4c and dshow the J-V and EQE curves of the OPVs with BPQDs of different sizes in the active layers,r espectively.D etailed photovoltaic parameters of the devices including average V oc , J sc ,F F, PCE and PCE enhancement are summarized in Table S5. With only 1vol %a ddition in the active layers,t he average PCEs of devices doped with BPQDs of 3, 4.5, 6nmare 9.69 %, 9.95 %, and 9.85 %, respectively,demonstrating the maximum relative PCE enhancement of 10.7 %i nc omparison with control devices.The PCE enhancement is mainly attributed to the increase of J sc ,w hich is similar to the case of PTB7:PC 71 BM-based OPVs.S imilarly,B PQDs can induce obvious improvement of EQEs in the whole absorption region of the devices due to the enhancement of light harvesting.M oreover,w eh ave observed improved stability of the OPVs by the BPQDs presumably due to the enhanced stability of the bulk heterojunction in the active layer.…”

“…Here,w er eport for the first time the application of BPQDs in OPVs to boost light harvesting.W es ynthesized BPQDs with various sizes and incorporated them into the active layers of two representative OPVs based on polythieno [3,4- [25,26] Significant enhancement up to 10 %w as observed in the PCEs of the OPVs prepared at optimum conditions,m ainly due to the enhanced light harvesting of the devices.T he optimum weight percentage of BPQDs relative to the organic donor (PTB7 or PBDTTT-EFT) in the devices is only about 0.055 %, which is much lower than the amount of any other additives used in OPVs before.T he astonishing effect can be attributed to the strong light absorption and scattering as well as the 2D nature of the BPQDs.T his work paves aw ay for using novel 2D QDs in OPVs in the future.…”

Black phosphorus: a two-dimensional reductant for in situ nanofabrication

“…18,19 BP has strong in-plane bonds in conjunction with weak van der Waals interlayer interactions thereby enabling exfoliation into few-layer BP sheets or phosphorene (single-layer BP). [20][21][22][23][24] Since 2014, BP has attracted tremendous research interest [25][26][27][28][29][30][31][32][33][34][35][36][37][38] because of its unique properties such as layerdependent direct bandgap, 28,39 anisotropy, 25,26,31,32,34,40 hingelike structure, 41 and quasi-one-dimensional excitonicnature, 42 all of which contrast markedly with those of other types of 2D materials. Nevertheless, BP degrades under ambient conditions as a result of the reaction with oxygen (P→P x O y ) and subsequent transformation to PO 4 3-in the presence of water.…”