Wei Zhi-ren

Measurement of the time-resolved spectrum of photoelectrons from ZnS:Mn, Cu luminescent material

The process of decay of photoelectrons in the conduction band of ZnS:Mn, Cu luminescent materials after excitation with a short-pulse laser has been investigated in this paper by means of measurements made using the microwave absorption dielectric spectrum detection technique. Exponential decay processes were observed for the electrons in the conduction band and the shallow-trapped electrons; the lifetimes of the electrons were found to be 1177 and 1703 ns, respectively. The processes of decay of the luminescence from ZnS:Mn, Cu were investigated and exponential decay processes were found for blue Cu+, green Cu+ and Mn2+ luminescent centres with lifetimes of the excited state of 139, 140 and 680 µs, respectively.

Recent progress of organohalide perovskite solar cells

Since 2009, greater attention has been paid to organic-inorganic hybrid CH3NH3PbI3 solar cells because of their simple fabrication process and high power conversion efficiency. Organohalide perovskite solar cells now develop very fast and their photovoltaic performance has been gradually improved. However, because of a band-gap limitation, the sunlight absorption spectrum of CH3NH3PbI3 is not broad enough to produce enhanced photovoltaic properties. In addition, Pb, as an important element, is toxic in organohalide perovskite. Thus, it is significant and meaningful to fabricate narrow-gap, environmentally friendly organohalide perovskite solar cells with better chemical stability. In the present paper, we mainly reviewed the progress in the band-gap engineering of perovskite materials to identify elements to replace toxic Pb and improve the absorption efficiency of incident light and the photovoltaic performance of solar cells. The influences of organic and inorganic hole transporting materials on the power conversion efficiencies of devices were compared, followed by a discussion of the recent progress in hole-conductor-free solar cells. To date, the theoretical research on organohalide perovskites is neither fully comprehensive nor far-reaching. We then conducted a review of the progress of theoretical research on the atomic structure, band structure, and band gap of CH3NH3PbI3 and other analog perovskite materials. The advantages and disadvantages of popular theoretical methods and their issues, which would be helpful for developing computational work, are also discussed. Finally, we include a number of open questions relevant to this field and present some research topics for the future.

Photoluminescence Mechanism of ZnO:Zn Investigated by Microwave Dielectric Spectrometry

We investigate the decay process of photoelectrons from a luminescent material of ZnO:Zn using a microwave dielectric spectrometry. Electrons in the conduction band are found to decay exponentially and the lifetime is 781 ns, while the time interval of decay from the maximum to half of this value is 470 ns. ZnO:Zn is a green luminescent material at its central wavelength of 510 nm. Compared to the decay of electrons in the conduction band, the decay process of the luminescence is faster, and the time interval of decay from the maximum to half of the maximum is about 100 ns. We believe that the mechanism of the ZnO:Zn visible luminescence is recombination luminescence, and find that our theoretical simulation is in agreement with the experimental results.