Xuhai Liu

Dimensionality and Interface Engineering of 2D Homologous Perovskites for Boosted Charge-Carrier Transport and Photodetection Performances

Two-dimensional (2D) homologous halide perovskite (HP) microcrystallines have emerged as a promising alternative light-sensitive material; however, the undesirable quantum confinement effect and severe interfacial charge-carrier scattering still hamper their applications in photodetectors (PDs). Here we propose a novel postsynthetic treatment to simultaneously solve both problems. 2D (OA)2FAn-1PbnBr3n+1 (OA and FA represent octadecylamine and formamidine) microplatelet film was immersed in solution containing FA+, leading to improvements in two aspects. First, the dimensionality of 2D HPs was increased through an exchange reaction between OA+ and FA+, which meliorates the quantum confinement effect and facilitates the separation of electrons and holes; second, the free-standing 2D HP microcrystallines were fused for promoted interdomain charge-carrier transport. The treated PDs achieved a 3600 and 4200% increase in external quantum yield and responsivity up to 7100% and 32 A/W, respectively, and the rise/decay time was shortened by two orders of magnitude to 0.25/1.45 ms.

Low-Voltage Photodetectors with High Responsivity Based on Solution-Processed Micrometer-Scale All-Inorganic Perovskite Nanoplatelets

All-inorganic photodetectors based on scattered CsPbBr3 nanoplatelets with lateral dimension as large as 10 µm are fabricated, and the CsPbBr3 nanoplatelets are solution processed governed by a newly developed ion-exchange soldering mechanism. Under illumination of a 442 nm laser, the photoresponsivity of photodetectors based on these scattered CsPbBr3 nanoplatelets is as high as 34 A W-1 , which is the largest value reported from all-inorganic perovskite photodetectors with an external driven voltage as small as 1.5 V. Moreover, the rise and fall times are 0.6 and 0.9 ms, respectively, which are comparable to most of the state-of-the-art all-inorganic perovskite-based photodetectors. All the material synthesis and device characterization are conducted at room temperature in ambient air. This work demonstrates that the solution-processed large CsPbBr3 nanoplatelets are attractive candidates to be applied in low-voltage, low-cost, ultra highly integrated optoelectronic devices.

Boosting Two-Dimensional MoS2/CsPbBr3 Photodetectors via Enhanced Light Absorbance and Interfacial Carrier Separation

Transition metal dichalcogenides (TMDs) are promising candidates for flexible optoelectronic devices because of their special structures and excellent properties, but the low optical absorption of the ultrathin layers greatly limits the generation of photocarriers and restricts the performance. Here, we integrate all-inorganic perovskite CsPbBr3 nanosheets with MoS2 atomic layers and take the advantage of the large absorption coefficient and high quantum efficiency of the perovskites, to achieve excellent performance of the TMD-based photodetectors. Significantly, the interfacial charge transfer from the CsPbBr3 to the MoS2 layer has been evidenced by the observed photoluminescence quenching and shortened decay time of the hybrid MoS2/CsPbBr3. Resultantly, such a hybrid MoS2/CsPbBr3 photodetector exhibits a high photoresponsivity of 4.4 A/W, an external quantum efficiency of 302%, and a detectivity of 2.5 × 1010 Jones because of the high efficient photoexcited carrier separation at the interface of MoS2 and CsPbBr3. The photoresponsivity of this hybrid device presents an improvement of 3 orders of magnitude compared with that of a MoS2 device without CsPbBr3. The response time of the device is also shortened from 65.2 to 0.72 ms after coupling with MoS2 layers. The combination of the all-inorganic perovskite layer with high photon absorption and the carrier transport TMD layer may pave the way for novel high-performance optoelectronic devices.

Field-Effect Transistors Based on van-der-Waals-Grown and Dry-Transferred All-Inorganic Perovskite Ultrathin Platelets

Nowadays, the research on perovskite transistors is still in its infancy, despite the fact that perovskite-based solar cells and light-emitting diodes have been widely investigated. Two major hurdles exist before obtaining reliable perovskite-based transistors: the processing difficulty for their sensitivity to polar solvents and unsatisfactory perovskite quality on the transistor platform. Here, for the first time, we report on high-performance all-inorganic perovskite FETs profiting from both van der Waals epitaxial boundary-free ultrathin single crystals and completely dry-processed transfer technique without chemical contaminant. These two crucial factors ensure the unprecedented high-quality perovskite channels. The achieved FET hole mobility and on-off ratio reach 0.32 cm2 V-1 s-1 and 6.7 × 103, respectively. Moreover, at the low temperature, the mobility and on-off ratio can be enhanced to be 1.04 cm2 V-1 s-1 and 1.3 × 104. This work could open the door for the FET applications based on perovskite single crystals.

Enhancing Optoelectronic Properties of Low-Dimensional Halide Perovskite via Ultrasonic-Assisted Template Refinement

Low-dimensional halide perovskite (HP) has triggered lots of research attention in recent years due to anisotropic optoelectronic/semiconducting properties and enhanced stability. High-quality low-dimensional HPs via controllable engineering are required to fulfill the encouraging promise for device applications. Here, we introduce, for the first time, postsynthetic ultrasonic-assisted refinement of two-dimensional homologous HPs (OA2PbBr4, OA is octadecylamine). The solution-prepared OA2PbBr4, either in the form of large-sized microcrystal or nanosheet, obtains significantly enhanced crystallinity after ultrasonic treatment. We further show that OA2PbBr4 nanosheets can be used as a template to construct low-dimensional CsPbBr3 with the size and morphology inherited. Importantly, we found the ultrasonic-treated OA2PbBr4 crystals, compared with pristine ones, lead to enhanced optoelectronic properties for the resultant low-dimensional CsPbBr3, as demonstrated by improved photodetection performances, including prolonged charge-carrier lifetime, improved photostability, increased external quantum yield/responsivity, and faster response speed. We believe this work provides novel engineering of low-dimensional HPs beyond the reach of straightforward synthesis.

Metal Halide Perovskites: Synthesis, Ion Migration, and Application in Field-Effect Transistors

The past several years have witnessed tremendous developments of metal halide perovskite (MHP)-based optoelectronics. Particularly, the intensive research of MHP-based light-emitting diodes, photodetectors, and solar cells could probably reform the optoelectronic semiconductor industry. In comparison, in spite of the large intrinsic charge carrier mobility of MHPs, the development of MHP-based field-effect transistors (MHP-FETs) is relatively slow, which is essentially due to the gate-field screening effect induced by the ion migration and accumulation in MHP-FETs. This work mainly aims to summarize the recent important work on MHP-FETs and propose solutions in terms of the development bottleneck of perovskite-based transistors, in an attempt to boost the research of MHP transistors further. First, the advantages and potential applications of MHP-FETs are briefly introduced, which is followed by a detailed description of the MHP crystalline structure and various material fabrication techniques. Afterward, MHP-FETs are discussed, including transistors based on hybrid organic-inorganic perovskites, all-inorganic perovskites, and lead-free perovskites.

Band offsets in new BN/BX (X = P, As, Sb) lateral heterostructures based on bond-orbital theory

Identifying heterostructures with tunable band alignments remains a difficult challenge. Here, based on bond-orbital theory, we propose a series of new BN/BX (X = P, As, Sb) lateral heterostructures (LHS). Our first principles calculations reveal that the LHS interlines have a substantial impact on the electronic properties. Importantly, we start with the chemical concepts, such as bond length and strength as well as orbital overlap interaction, in an attempt to thoroughly investigate the electronic properties, namely the band offset, the band gap (Eg) and the state of the energy level. We demonstrate that the newly designed BN/BX LHS have profound implications for developing advanced optoelectronics, such as high-performance light-emitting diodes and lasers. Furthermore, the new BN/BX LHS designed from the chemical viewpoint can shed new light on overcoming the enormous hurdle of ineffective and laborious material design.

A class of Pb-free double perovskite halide semiconductors with intrinsic ferromagnetism, large spin splitting and high Curie temperature

Room-temperature ferromagnetic (FM) semiconductors are of vital importance for realizing advanced spintronic devices. The recent discovery of diluted ferromagnetism in Mn-doped CH3NH3PbI3 suggests hopes for developing halide perovskite based spintronics. However, the measured Curie temperature was usually below 15 K, which severely prohibits the Mn-doped CH3NH3PbI3 from being applied in room-temperature applications. In this work, instead of using the usual doping strategy, we present a new class of Pb-free FM halide semiconductors with double perovskite structures (Cs2GeMX6, transition metal M = V, Mn or Ni; X = Cl, Br or I), which possess spin splitting in a broad range of 0.06–1.00 eV and ultrahigh Curie temperature of 490–800 K. Furthermore, the Curie temperature can still be higher than room temperature under the lattice expansion effect. These excellent intrinsic properties are because of the large number of nearest neighboring magnetic ions and strong exchange coupling between the M 3d and GeX6 σs–p* orbitals. Our designed Pb-free FM halide semiconductors with double perovskite structures can be envisaged to develop into other highly dynamic research fields with vast implications for high-performance spin optoelectronics and spintronics.

Bubble dimer dynamics induced by dual laser beam ablation in liquid

An approach based on dual laser beam ablation in liquid is presented for the preparation of bimetal hydroxide. The dynamics of a dual laser-induced bubble dimer is studied by the combination of an inviscid Rayleigh-Plesset model, an ultrafast camera, and time-resolved shadowgraphy experiments. It indicates that the dual laser-induced bubble pair will rapidly merge into a dimer and then undergo evolution as a single bubble, which can promote the agglomeration of two kinds of metal particles in this thermodynamic environment. Moreover, the atomic ratio of bimetal hydroxide with high crystallinity can be precisely adjusted by the dual laser energy ratio without any additives.