Jiawei Wan

Low-Temperature Solution-Processed Tin Oxide as an Alternative Electron Transporting Layer for Efficient Perovskite Solar Cells

Lead halide perovskite solar cells with the high efficiencies typically use high-temperature processed TiO2 as the electron transporting layers (ETLs). Here, we demonstrate that low-temperature solution-processed nanocrystalline SnO2 can be an excellent alternative ETL material for efficient perovskite solar cells. Our best-performing planar cell using such a SnO2 ETL has achieved an average efficiency of 16.02%, obtained from efficiencies measured from both reverse and forward voltage scans. The outstanding performance of SnO2 ETLs is attributed to the excellent properties of nanocrystalline SnO2 films, such as good antireflection, suitable band edge positions, and high electron mobility. The simple low-temperature process is compatible with the roll-to-roll manufacturing of low-cost perovskite solar cells on flexible substrates.

Three-Dimensional Graphene/Metal Oxide Nanoparticle Hybrids for High-Performance Capacitive Deionization of Saline Water

A novel and general method is proposed to construct three-dimensional graphene/metal oxide nanoparticle hybrids. For the first time, it is demonstrated that this graphene-based composite with open pore structures can be used as the high-performance capacitive deionization (CDI) electrode materials, which outperform currently reported materials. This work will offer a promising way to develop highly effective CDI electrode materials.

Efficient hole-blocking layer-free planar halide perovskite thin-film solar cells

Efficient lead halide perovskite solar cells use hole-blocking layers to help collection of photogenerated electrons and to achieve high open-circuit voltages. Here, we report the realization of efficient perovskite solar cells grown directly on fluorine-doped tin oxide-coated substrates without using any hole-blocking layers. With ultraviolet-ozone treatment of the substrates, a planar Au/hole-transporting material/CH₃NH₃PbI₃-xClx/substrate cell processed by a solution method has achieved a power conversion efficiency of over 14% and an open-circuit voltage of 1.06 V measured under reverse voltage scan. The open-circuit voltage is as high as that of our best reference cell with a TiO₂ hole-blocking layer. Besides ultraviolet-ozone treatment, we find that involving Cl in the synthesis is another key for realizing high open-circuit voltage perovskite solar cells without hole-blocking layers. Our results suggest that TiO₂ may not be the ultimate interfacial material for achieving high-performance perovskite solar cells.

Pt–Ni Alloy Nanoparticles as Superior Counter Electrodes for Dye‐Sensitized Solar Cells: Experimental and Theoretical Understanding

Pt-Ni alloy nanoparticles are synthesized and used as counter electrodes in dye-sensitized solar cells (DSSCs) for the first time. A PCE of 9.15% is achieved with the Pt3 Ni counter electrode, displaying an evident improvement compared with the conventional pure Pt (8.33%). The cell stability is also obviously increased with the Pt3 Ni counter electrode.

Performance enhancement of perovskite solar cells with Mg-doped TiO2 compact film as the hole-blocking layer

In this letter, we report perovskite solar cells with thin dense Mg-doped TiO2 as hole-blocking layers (HBLs), which outperform cells using TiO2 HBLs in several ways: higher open-circuit voltage (Voc) (1.08 V), power conversion efficiency (12.28%), short-circuit current, and fill factor. These properties improvements are attributed to the better properties of Mg-modulated TiO2 as compared to TiO2 such as better optical transmission properties, upshifted conduction band minimum (CBM) and downshifted valence band maximum (VBM), better hole-blocking effect, and higher electron life time. The higher-lying CBM due to the modulation with wider band gap MgO and the formation of magnesium oxide and magnesium hydroxides together resulted in an increment of Voc. In addition, the Mg-modulated TiO2 with lower VBM played a better role in the hole-blocking. The HBL with modulated band position provided better electron transport and hole blocking effects within the device.

In situ growth of double-layer MoO3/MoS2 film from MoS2 for hole-transport layers in organic solar cell

Efficient organic solar cells (OSCs) based on regioregular poly(3-hexylthiophene):fullerene derivative [6,6]-phenyl-C61butyric acid methyl ester composites have been fabricated on fluorine-doped tin oxide (FTO) coated glass substrates by a radio frequency (RF) sputtered and ultraviolet ozone (UVO) treated MoS2 film as the hole-transport layer (HTL). With the help of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, Raman spectroscopy, transmission spectra and the Hall-effect system, we find that the deposition temperature can modulate the contents of the various valence states of molybdenum, which can result in changes of the energy level, and the optical and electrical properties of the MoS2 films. MoS2 has been oxidized to a double-layered MoO3–MoS2 film by UVO treatment. Due to the presence of the molybdenum oxidation states Mo5+ and Mo6+, the MoS2 film shows p-type conductive behavior, and its smaller electron affinity can effectively block electron from exciton dissociation. By optimizing the HTL thickness and sputtering deposition temperature, a power conversion efficiency up to 4.15% has been achieved for an OSC that used a double-layered MoO3–MoS2 film as the HTL. Its JSC is bigger than that of the OSC with a pure MoO3 film as the HTL. This shows that this double layer MoO3–MoS2 interface is more favorable for hole-transfer.

Electrospun PEDOT:PSS–PVA nanofiber based ultrahigh-strain sensors with controllable electrical conductivity

A novel strain sensor based on poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)–polyvinyl alcohol (PEDOT:PSS–PVA) nanofibers has been fabricated on Kapton substrate by electrospinning, and fully packaged by encapsulating with a polydimethylsioxane layer. Via controlling the concentration of the additive dimethylsulfoxide, the electrical conductivity of the as-spun PEDOT:PSS–PVA nanofiber network can be tuned over a wide rang from 4.8 × 10−8 to 1.7 × 10−5 S cm−1. This kind of strain sensor has excellent stability, fast response, and a high gauge factor of up to about 396. In the meantime, the device could be driven by solar cells, and could detect tiny and quick human actions, for example bending of a finger.

High-Performance Amorphous Indium Gallium Zinc Oxide Thin-Film Transistors With

We have fabricated and investigated amorphous indium gallium zinc oxide (α-IGZO) thin-film transistors (TFTs) by using HfO_xN_y/HfO₂/HfO_xN_y (NON) as the gate dielectric. The NON tristack dielectric structure can increase the gate capacitance density, effectively improve interface properties of both the gate/dielectric and dielectric/active channels, suppress the charge trap density, and reduce the gate leakage. The α-IGZO TFT (W/L = 200/10 μm) with NON shows superior performance such as a saturation current of 0.33 mA, an ON/OFF-current ratio of 2.2 × 10⁶, a saturation mobility of 10.2 cm²/V · s, a source/contact resistivity of 83 Ω · cm, a subthreshold swing of 0.13 V/dec, and enhanced stressing reliability.

\hbox{HfO}_{x}\hbox{N}_{y}/\hbox{HfO}_{2}/\hbox{HfO}_{x}\hbox{N}_{y}

Fluorite CeO2 nanorods (NRs) with tunable surface defects are successfully prepared via hydrothermal synthesis followed by post-calcination under different atmospheres. Impressively, the CeO2 NRs obtained under mixed Ar and H-2 gas at 800 degrees C exhibit superior catalytic activity towards water oxidation under visible light (lambda >= 420 nm), which is 10 times higher than that of CeO2 NRs treated under air at 800 degrees C. Detailed characterization and theoretical analysis reveal that the rich surface defects including surface oxygen vacancies and Ce3+ ions are the origin of the enhanced water oxidation performance of the CeO2 NRs treated under the reduced atmosphere.

Tristack Gate Dielectrics

Preparing metal single-atom materials is currently attracting tremendous attention and remains a significant challenge. Herein, we report a novel core-shell strategy to synthesize single-atom materials. In this strategy, metal hydroxides or oxides are coated with polymers, followed by high-temperature pyrolysis and acid leaching, metal single atoms are anchored on the inner wall of hollow nitrogen-doped carbon (CN) materials. By changing metal precursors or polymers, we demonstrate the successful synthesis of different metal single atoms dispersed on CN materials (SA-M/CN, M = Fe, Co, Ni, Mn, FeCo, FeNi, etc.). Interestingly, the obtained SA-Fe/CN exhibits much higher catalytic activity for hydroxylation of benzene to phenol than Fe nanoparticles/CN (45% vs 5% benzene conversion). First-principle calculations further reveal that the high reactivity originates from the easier formation of activated oxygen species at the single Fe site. Our methodology provides a convenient route to prepare a variety of metal single-atom materials representing a new class of catalysts.