Junfeng Wei

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.

Internal friction and Jahn–Teller effect in the charge-ordered La1−xCaxMnO3 (0.5⩽x⩽0.87)

The Jahn–Teller effect in the charge-ordered (CO) state for La1−xCaxMnO3 (0.5⩽x⩽0.87) was studied by measuring the low-temperature powder x-ray diffraction, internal friction, and shear modulus. We find that the electron–lattice interaction with the static Jahn–Teller distortion is the strongest near x≈0.75 in the CO state. It was particularly observed that a crossover of the Jahn–Teller vibration mode from Q2 to Q3 near x=0.75 induces crossovers of the crystal structure from tetragonally compressed to tetragonally elongated orthorhombic, and of the magnetic structure from CE-type to C-type near x=0.75. The experimental results give strong evidence that the Jahn–Teller effect not only plays a key role in stabilizing the CO state, but also determines the magnetic and crystal structures in the CO state for La1−xCaxMnO3.

Population dynamics of Myzus persicae on tobacco in Yunnan Province, China, before and after augmentative releases of Aphidius gifuensis

Abstract The population dynamics of Myzus persicae were investigated in the field in a year without releases of Aphidius gifuensis (1998–1999), in a year with A. gifuensis releases (2000–2001) and several years later (2005–2007). The results showed that both high mean population densities and damage rates did not differ between 1998 and 1999, but were significantly lower in 2000–2001 and 2005–2007. Moreover, farmers also reported the decrease of M. persicae populations and attributed the declines to augmentative releases of A. gifuensis in their own fields, indicating farmers’ recognition in the effectiveness of A. gifuensis for M. persicae control. In addition, compared with the historical data on pesticide use for M. persicae control, the number of insecticide applications and cost of M. persicae control was sustained at a low level in 2007 (several years after release of A. gifuensis). This suggests that the augmentative releases of A. gifuensis could be effective and sustainable in M. persicae control.

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.

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.