Dimethyl Ferrocene-Induced Ambient-Processed High-Quality Films toward Efficient Perovskite Solar Cells for Industrial Application.

Metal halide perovskite solar cells (PSCs) have recently made significant progress with power conversion efficiencies (PCEs) boosted from 3.8% to a certified one over 26.1%, partially benefiting from the high-quality perovskite film enabled by the effective one-step spin-coating route. However, an extra antisolvent step with poor controllability and producibility is often involved in such a process, and some intrinsic defects are generated inevitably, especially in ambient atmospheric conditions, thus fundamentally limiting the commercialization of PSCs. Here, we introduce 1,1'dimethyl ferrocene into methylammonium lead halide precursor, which could not only recover the defects within perovskite film but also simplify the process without the extra antisolvent step. Accordingly, a dense and uniform perovskite film with large grains has been obtained under ambient conditions, which has much lower defect density, better stability against moisture penetration, and enhanced thermal tolerance than the control one, delivering a champion PCE of 16.92%. Current work sheds light on the simplified air-processed strategy for high-quality perovskite films, which might pave the way for exploring efficient and stable PSCs toward industrial applications.

Enhancing the Stability of Orthorhombic CsSnI3 Perovskite via Oriented π-Conjugated Ligand Passivation.

Lead-free orthorhombic CsSnI3 (Bγ-CsSnI3) perovskite has been emerging as one of the potential candidates of photovoltaic materials with superior performance. However, the instability induced by rapid reconstructive phase transition and the oxidation of Sn2+ greatly limits their future application. We thus reported a strategy, oriented π-conjugated ligand passivation, for enhancing the stability of Bγ-CsSnI3, simulated using a Bγ-CsSnI3 slab model based on the first-principles computation. The phase stability was found to be strongly dependent on the orientations of phenylethylammonium (PEA+) ligands. The passivated Bγ-CsSnI3 slab with the ligand molecule axis along [414] was demonstrated as the most stable with the lowest adsorption energy (Eads). Based on this configuration, the calculated formation energies (Eform) of half- and full-monolayer coverage were even more negative than that of yellow phase (Y-) CsSnI3 passivated by PEA+ ligands, verifying the enhanced phase stability. Furthermore, the surface states could be effectively suppressed and the downshifted conduction band minimum (CBM) resulted in a reduced band gap for the completely capped Bγ-CsSnI3. Moreover, the CBM and the valence band maximum (VBM) of the system with complete coverage were respectively donated by the surface and bulky components of the slab, which might benefit the separation and transfer of photogenerated carriers.

Stable Bandgap-Tunable Hybrid Perovskites with Alloyed Pb-Ba Cations for High-Performance Photovoltaic Applications.

The intrinsic poor stability of MAPbI3 hybrid perovskites in the ambient environment remains as the major challenge for photovoltaic applications. In this work, complementary first-principles calculations and experimental characterizations reveal that metal cation alloyed perovskite (MABa xPb1- xI3) can be synthesized and exhibit substantially enhanced stability via forming stronger Ba-I bonds. The Ba-Pb alloyed perovskites remain phase-pure in ambient air for more than 15 days. Furthermore, the bandgap of MABa xPb1- xI3 is tailored in a wide window of 1.56-4.08 eV. Finally, MABa xPb1- xI3 is used as a capping layer on MAPbI3 in solar cells, resulting in significantly improved power conversion efficiency (18.9%) and long-term stability (>30 days). Overall, our results provide a simple but reliable strategy toward stable less-Pb perovskites with tailored physical properties.

Elimination of S Vacancy as the Cause for the n-Type Behavior of MoS2 from the First-Principles Perspective.

Molybdenum disulfide (2H-MoS2) based low-dimensional nanostructure materials have great potential for applications in electronic and optoelectronic devices. However, some of the properties such as the origin of the native n-type electrical conductivity (EC) observed in these materials still remain elusive. Here, the defect properties in the 2H-MoS2 bulk system are systematically investigated by first-principles calculation to address these issues. We find that the S vacancy VS with low formation energy cannot be the origin of n-type EC owing to its deep defect levels within the valence band region. All other donor defects such as antisite MoS or Mo interstitial MoI also have deep levels that can trap electrons leading to depressed EC. SMo and SI could be the origin of the p-type EC in 2H-MoS2, but the concentrations are expected to be rather low due to their high formation energies and can only be enhanced under S-rich/Mo-poor conditions. These results provide the underlying insights on the defect properties 2H-MoS2 and explain well the experimental observations.

Superior Photodetectors Based on All-Inorganic Perovskite CsPbI3 Nanorods with Ultrafast Response and High Stability.

Currently, one-dimensional all-inorganic CsPbX3 (X = Br, Cl, and I) perovskites have attracted great attention, owning to their promising and exciting applications in optoelectronic devices. Herein, we reported the exploration of superior photodetectors (PDs) based on a single CsPbI3 nanorod. The as-constructed PDs had a totally excellent performance with a responsivity of 2.92 × 103 A·W-1 and an ultrafast response time of 0.05 ms, respectively, which were both comparable to the best ones ever reported for all-inorganic perovskite PDs. Furthermore, the detectivity of the PDs approached up to 5.17 × 1013 Jones, which was more than 5 times the best one ever reported. More importantly, the as-constructed PDs showed a high stability when maintained under ambient conditions.

Superior B-Doped SiC Nanowire Flexible Field Emitters: Ultra-Low Turn-On Fields and Robust Stabilities against Harsh Environments.

Low turn-on fields together with boosted stabilities are recognized as two key factors for pushing forward the implementations of the field emitters in electronic units. In current work, we explored superior flexible field emitters based on single-crystalline 3C-SiC nanowires, which had numbers of sharp edges, as well as corners surrounding the wire body and B dopants. The as-constructed field emitters behaved exceptional field emission (FE) behaviors with ultralow turn-on fields (Eto) of 0.94-0.68 V/µm and current emission fluctuations of ±1.0-3.4%, when subjected to harsh working conditions under different bending cycles, various bending configurations, as well as elevated temperature environments. The sharp edges together with the edges were able to significantly increase the electron emission sites, and the incorporated B dopants could bring a more localized state close to the Fermi level, which rendered the SiC nanowire emitters with low Eto, large field enhancement factor as well as robust current emission stabilities. Current B-doped SiC nanowires could meet all essential requirements for an ideal flexible emitters, which exhibit their promising prospect to be applied in flexible electronic units.

Enhancing the Performance of Quantum Dot Light-Emitting Diodes Using Room-Temperature-Processed Ga-Doped ZnO Nanoparticles as the Electron Transport Layer.

Colloidal ZnO nanoparticle (NP) films are recognized as efficient electron transport layers (ETLs) for quantum dot light-emitting diodes (QD-LEDs) with good stability and high efficiency. However, because of the inherently high work function of such films, spontaneous charge transfer occurs at the QD/ZnO interface in such a QD-LED, thus leading to reduced performance. Here, to improve the QD-LED performance, we prepared Ga-doped ZnO NPs with low work functions and tailored band structures via a room-temperature (RT) solution process without the use of bulky organic ligands. We found that the charge transfer at the interface between the CdSe/ZnS QDs and the doped ZnO NPs was significantly weakened because of the incorporated Ga dopants. Remarkably, the as-assembled QD-LEDs, with Ga-doped ZnO NPs as the ETLs, exhibited superior luminances of up to 44 000 cd/m2 and efficiencies of up to 15 cd/A, placing them among the most efficient red-light QD-LEDs ever reported. This discovery provides a new strategy for fabricating high-performance QD-LEDs by using RT-processed Ga-doped ZnO NPs as the ETLs, which could be generalized to improve the efficiency of other optoelectronic devices.

Highly Efficient Photocatalytic Hydrogen Evolution in Ternary Hybrid TiO2/CuO/Cu Thoroughly Mesoporous Nanofibers.

Development of novel hybrid photocatalysts with high efficiency and durability for photocatalytic hydrogen generation is highly desired but still remains a grand challenge currently. In the present work, we reported the exploration of ternary hybrid TiO2/CuO/Cu thoroughly mesoporous nanofibers via a foaming-assisted electrospinning technique. It is found that by adjusting the Cu contents in the solutions, the unitary (TiO2), binary (TiO2/CuO, TiO2/Cu), and ternary (TiO2/CuO/Cu) mesoporous products can be obtained, enabling the growth of TiO2/CuO/Cu ternary hybrids in a tailored manner. The photocatalytic behavior of the as-synthesized products as well as P25 was evaluated in terms of their hydrogen evolution efficiency for the photodecomposition water under Xe lamp irradiation. The results showed that the ternary TiO2/CuO/Cu thoroughly mesoporous nanofibers exhibit a robust stability and the most efficient photocatalytic H2 evolution with the highest release rate of ∼851.3 µmol g(-1) h(-1), which was profoundly enhanced for more than 3.5 times with respect to those of the pristine TiO2 counterparts and commercial P25, suggesting their promising applications in clean energy production.

SiC Nanowire Film Photodetectors: A Promising Candidate Toward High Temperature Photodetectors.

In this study, UV photodetectors (PDs) based on SiC nanowire films have been successfully prepared by a simple and low-cost drip-coating method followed by sintering at 500 °C. The corresponding electrical characterizations clearly demonstrate that the SiC nanowire based PD devices can be regarded as a promising candidate for UV PDs. The PDs can exhibit the excellent performances of fast, high sensitivity, linearity, and stable response, which can thus achieve on-line monitoring of weak UV light. Furthermore, the SiC nanowire-based PDs enable us to fabricate detectors working under high temperature as high as 150 °C. The high photosensitivity and rapid photoresponse for the PDs can be attributed to the superior single crystalline quality of SiC nanowires and the ohmic contact between the electrodes and nanowires.

Study of Ac Dielectrophoretic Process of SiC Nanowires: A Universal Method for Alignment of Semiconductor Nanowires.

In this study, the dielectrophoretic processes of SiC nanowires suspended in three typical solvents, (highly purified water, ethanol and isopropanol) were systematically investigated. Optical microscope and SEM characterizations were used to observe the order of SiC nanowires on the surface of gold microchannels. The gold microchannels were induced by Ac dielectrophoresis of the corresponding dispersion solutions of SiC nanowires, with a concentration of 0.1 mg/mL. The study shows that the dielectrophoresis process is an effective way of synthesizing highly oriented SiC nanoarrays using isopropanol solution. The results also show that the arrangement of SiC nanowires on the interdigital electrode configuration not only depend on the kind of solvent used, but also on the applied frequency (1000 Hz~1 MHz) and voltage (1 V~20 V).