Mei Lv

Numerical simulation: Toward the design of high-efficiency planar perovskite solar cells

Organo-metal halide perovskite solar cells based on planar architecture have been reported to achieve remarkably high power conversion efficiency (PCE, >16%), rendering them highly competitive to the conventional silicon based solar cells. A thorough understanding of the role of each component in solar cells and their effects as a whole is still required for further improvement in PCE. In this work, the planar heterojunction-based perovskite solar cells were simulated with the program AMPS (analysis of microelectronic and photonic structures)-1D. Simulation results revealed a great dependence of PCE on the thickness and defect density of the perovskite layer. Meanwhile, parameters including the work function of the back contact as well as the hole mobility and acceptor density in hole transport materials were identified to significantly influence the performance of the device. Strikingly, an efficiency over 20% was obtained under the moderate simulation conditions.

Mesoporous SnO2 nanoparticle films as electron-transporting material in perovskite solar cells

Perovskite solar cells with mesoporous metal oxide films as scaffold layers have demonstrated very impressive advances in performance recently. Here, we present an investigation into mesoporous perovskite solar cells incorporating mesoporous SnO2 nanoparticle films as electron-transporting materials and scaffold layers, to replace traditional mesoporous TiO2 films. We have optimized the SnO2 film thickness and treated the surface of the SnO2 film with an aqueous solution of TiCl4. Due to the TiCl4 treatment the recombination process was significantly retarded. The short-circuit current density (Jsc) and open-circuit voltage (Voc) reached nearly 18 mA cm−2 and 1 V, respectively. Consequently, the power conversion efficiency of the device with the SnO2 film exceeded 10%.

Colloidal CuInS2 Quantum Dots as Inorganic Hole-Transporting Material in Perovskite Solar Cells

To develop novel hole-transporting materials (HTMs) is an important issue of perovskite solar cells (PSCs), especially favoring the stability improvement and the cost reduction. Herein, we use ternary quantum dots (QDs) as HTM in mesoporous TiO2/CH3NH3PbI3/HTM/Au solar cell, and modify the surface of CuInS2 QDs by cation exchange to improve the carrier transport. The device efficiency using CuInS2 QDs with a ZnS shell layer as HTM is 8.38% under AM 1.5, 100 mW cm(-2). The electrochemical impedance spectroscopy suggested that the significantly enhanced performance is mainly attributed to the reduced charge recombination between TiO2 and HTM. It paves a new pathway for the future development of cheap inorganic HTMs for the high efficiency PSCs.

Tribological Performance and Lubrication Mechanism of Solid-Liquid Lubricating Materials in High-Vacuum and Irradiation Environments

Abstract In this paper, six solid–liquid lubricating materials have been prepared based on two kinds of liquid lubricants including perfluoropolyethers oil (PFPE) and chlorinated-phenyl and methyl-terminated silicone oil (CPSO) and three different solid lubrication materials [polyimide (PI), polytetrafluoroethylene and Cu-based alloy] by the dip-coating method. The tribological behaviors of these lubricating materials were comparatively investigated in high-vacuum condition. The results showed that the polymer-based solid–liquid lubricating materials exhibited the excellent tribological properties, which mainly attributed to the hydrodynamic lubrication. Moreover, as for the same solid substrate, the smaller the value of the steady-state contact angle was, the higher the friction coefficient was. Meanwhile, the effect of atomic oxygen (AO) and proton (H+) irradiations on structure and tribological properties of the PI/CPSO and PI/PFPE was further investigated in this work. The experimental results indicated that irradiations induced the degradation of the lubricating oil, which resulted in the increment of the friction coefficient and wear rate, thus decreasing the lubricating performance. In addition, the effect induced by H+ irradiation was more serious than that by AO irradiation. PI/CPSO solid–liquid lubricating material has good irradiation stability compared with PI/PFPE.

BiVO4 semiconductor sensitized solar cells

Semiconductor sensitized solar cells (SSSCs) are promising candidates for the third generation of cost-effective photovoltaic solar cells and it is important to develop a group of robust, environment friendly and visible-light-responsive semiconductor sensitizers. In this paper, we first synthesized bismuth vanadate (BiVO4) quantum dots by employing facile successive ionic layer adsorption and reaction (SILAR) deposition technique, which we then used as a sensitizer for solar energy conversion. The preliminary optimised oxide SSSC showed an efficiency of 0.36%, nearly 2 orders of magnitude enhancement compared with bare TiO2, due to the narrow bandgap absorption of BiVO4 quantum dots and intimate contact with the oxide substrate. This result not only demonstrates a simple method to prepare BiVO4 quantum dots based solar cell, but also provides important insights into the low bandgap oxide SSSCs.

Highly stable tribological performance and hydrophobicity of porous polyimide material filled with lubricants in a simulated space environment

Space exploitation and development need high-performance materials for spacecraft so as to maintain the long service life and reliability of mechanical equipment. The purpose of the present study was to exploit a new material with durable life, stable friction coefficient and low wear rate in harsh space environments. Two kinds of solid–liquid synergetic lubricating composites have been prepared using perfluoropolyethers (PFPE) or chlorinated phenyl and methyl terminated silicone oil (CPSO) filled in porous polyimide (PPI). The tribological performance and hydrophobicity of the oil-filled PPI were evaluated by contact angle analyses and a ball-on-disk tribometer before and after proton irradiation in a simulated space environment. After proton irradiation, two composites can maintain stable hydrophobic performance. More importantly, the friction coefficients of CPSO/PPI and PFPE/PPI increased slightly from 0.07 and 0.05 to 0.1 and 0.14, respectively. The wear rates of CPSO/PPI and PFPE/PPI also increased slightly from 5.13 × 10−5 mm3 N−1 m−1 and 4.23 × 10−5 mm3 N−1 m−1 to 5.75 × 10−5 mm3 N−1 m−1 and 6.19 × 10−5 mm3 N−1 m−1, respectively. The CPSO/PPI composite showed the smallest change in hydrophobicity, friction coefficient and wear rate before and after proton irradiation. The mechanism of highly stable hydrophobicity and tribological performance was mainly based on a continuous self-healing surface; the stored oil in the pores of PPI can creep to the surface of the material to repair the damage induced by proton irradiation, which ensured that the material had stable and durable hydrophobicity and tribological properties in a proton irradiation environment.

Effects of individual and sequential irradiation with atomic oxygen and protons on the surface structure and tribological performance of polyetheretherketone in a simulated space environment

The changes in the surface structure and the tribological performance of polyetheretherketone (PEEK) induced by individual and sequential irradiations with atomic oxygen (AO) and protons (Prs) were investigated in a space environment simulation facility. The experimental results showed that Pr irradiation induced the surface carbonization of PEEK which induced the greatest degree of decrease in the surface roughness from 29.61 nm to 16.15 nm, surface energy from 49.16 mJ m−2 to 46.96 mJ m−2, friction coefficient from 0.28 to 0.08 and wear rate from 10.28 × 10−5 mm3 N−1 m−1 to 5.45 × 10−5 mm3 N−1 m−1. The AO irradiation induced the surface oxidation of PEEK, and then increased the surface roughness from 29.61 nm to 58.77 nm, surface energy from 49.16 mJ m−2 to 73.75 mJ m−2, friction coefficient from 0.28 to 0.35 and wear rate from 10.28 × 10−5 mm3 N−1 m−1 to 18.22 × 10−5 mm3 N−1 m−1. The surface structural variations and tribological performance of PEEK induced by the sequential Pr–AO and AO–Pr irradiations were respectively similar to the results of the individual AO and Pr irradiations, and the final form of irradiation has a bigger effect on the changes in the surface structure and tribological performance during the sequential irradiation tests. The erosion stacking effect of the sequential irradiations was observed, and the AO–Pr irradiations caused the biggest changes in infrared spectra and the surface composition of C and O elements in X-ray photoelectron spectroscopy. The Pr–AO irradiations gave the biggest increment in the surface energy from 49.16 mJ m−2 to 74.03 mJ m−2 and wear rate from 10.28 × 10−5 mm3 N−1 m−1 to 24.07 × 10−5 mm3 N−1 m−1.

The structure properties and tribological behavior of the ionic liquid–polyimide composite films under high-vacuum environment

Ionic liquid (IL) can be used as external or internal lubricant. The tribological performance of polyimide (PI)–steel contact surface driven by IL lubricant was investigated using a ball-on-disk tribometer in high-vacuum environment. The experimental results indicated that IL as the external lubricant could obviously decrease the friction coefficient of PI from 0.41 to 0.01 and corrode the surface of steel ball. As internal lubricant, some IL/PI composite films were prepared, and the structure properties and tribological behavior were investigated. IL can be uniformly dispersed in the polymer and could make film surface more hydrophilic along with the increasing content of IL in PI. The IL/PI composite film with 1% content of IL has the lowest friction coefficient and causes the least damage against the steel ball.

Semiconductor Sensitized Solar Cells Based on BiVO4-Sensitized Mesoporous SnO2 Photoanodes.

Low cost, stable and visible-light-responsive bismuth vanadate (BiVO4) was used as the light absorbing material to fabricate a low bandgap oxide solar cell on mesoporous SnO2 photoanode. BiVO4 nanoparticles were grown on the mesoporous SnO2 films employing successive ionic layer adsorption and reaction process. The optimized BiVO4 solar cell shows an incident photon to current conversion efficiency of more than 60% at a wide range of visible region (350 nm-450 nm), leading to a power conversion efficiency of 0.56% at AM1.5, 100 mW x cm(-2). This result provides important insights into the low cost and robust oxide solar cells.

Efficient Perovskite/Quantum Dot Hybrid Solar Cells

The high efficiency of perovskite solar cells heavily relies on expensive organic hole-transporting materials. We report colloidal PbS and CuInS2 quantum dots being used as inorganic hole-transporting material in efficient hybrid perovskite solar cells.