Wenwen Zhang

(001)-textured growth of diamond films on polycrystalline diamond substrates by bias-assisted chemical vapor deposition

(001)-textured diamond films were deposited on as-grown polycrystalline and polished polycrystalline diamond substrates by means of bias-assisted chemical vapor deposition (CVD). Scanning electron microscopy (SEM) and Raman scattering were carried out to investigate the morphology and phase purity before and after the growth process. It is observed that an in-plane oriented diamond domain can be formed on a diamond face with undefined crystal direction. The roughness of the substrate will affect the morphology of the top layer. The mechanism for (001)-textured growth during bias-assisted process is discussed.

Study on scalable Coulombic degradation for estimating the lifetime of organic light-emitting devices

The luminance decays of organic light-emitting diodes (OLEDs) are investigated with initial luminance of 1000 to 20?000?cd?m?2 through a scalable Coulombic degradation and a stretched exponential decay. We found that the estimated lifetime by scalable Coulombic degradation deviates from the experimental results when the OLEDs work with high initial luminance. By measuring the temperature of the device during degradation, we found that the higher device temperatures will lead to instabilities of organic materials in devices, which is expected to result in the difference between the experimental results and estimation using the scalable Coulombic degradation.

High-Quality Cs2AgBiBr6 Double Perovskite Film for Lead-Free Inverted Planar Heterojunction Solar Cells with 2.2 % Efficiency

All-inorganic double-metal perovskite materials have recently gained much attention due to their three dimensionality (3D) and non-toxic nature to replace lead-based perovskite materials. Among all those double perovskite materials, theoretical works have demonstrated that Cs2 AgBiBr6 shows high stability and possesses a suitable band gap for solar-cell applications. However, the film-forming ability of Cs2 AgBiBr6 is found to be the utmost challenge hindering its development in thin-film solar-cell devices. In this work, a high-quality Cs2 AgBiBr6 film with ultra-smooth morphology, micro-sized grains, and high crystallinity is realized via anti-solvent dropping technology and post-annealing at high temperature. After optimization, the first example of an inverted planar heterojunction solar-cell device based on Cs2 AgBiBr6 exhibits a power conversion efficiency of 2.23u2009% with VOC =1.01u2005V, JSC =3.19u2005mA/cm2 , and FF=69.2u2009%. Besides, the device shows no hysteresis and a high stability.