Synergistic Passivation on Buried Interface for Highly Efficient and Stable p-i-n Perovskite Solar Cells.

The properties of an interface at the hole transport layer (HTL)/perovskite layer are crucial for the performance and stability of perovskite solar cells (PVSCs), especially the buried interface between HTL and perovskite layer. Here, a molecular named potassium 1-trifluoroboratomethylpiperidine (3FPIP) assistant-modified perovskite bottom interface strategy is proposed to improve the charge transfer capability and balances energy level between HTL and perovskite. BF3 - in the 3FPIP molecule interacts with undercoordinated Pb2+ to passivate iodine vacancies and enhance PVSCs performance. Furthermore, the infiltration of K+ ions into perovskite molecules enhances the crystallinity and stability of perovskite. Therefore, the PVSCs with the buried interface treatment exhibit a champion performance of 24.6%. More importantly, the corresponding devices represent outstanding ambient stability, remaining at 92% of the initial efficiency after 1200 h. This work provides a new method of buried interface engineering with functional group synergy.

The In-Situ Observation of Grain Rotation and Microstructure Evolution Induced by Electromigration in Sn-3.0Ag-0.5Cu Solder Joints.

The in-situ observation of Sn-3.0Ag-0.5Cu solder joints under electromigration was conducted to investigate the microstructure and grain orientation evolution. It was observed that there was a grain rotation phenomenon during current stressing by in-situ electron backscattered diffraction (EBSD). The rotation angle was calculated, which indicated that the grain reorientation led to the decrease of the resistance of solder joints. On the other hand, the orientation of ß-Sn played a critical role in determining the migration of Cu atoms in solder joints under current stressing migration. When the angle between the electron flow direction and the c-axis of Sn (defined as α) was close to 0°, massive Cu6Sn5 intermetallic compounds were observed in the solder bulk; however, when α was close to 90°, the migration of the intermetallic compound (IMC) was blocked but many Sn hillocks grew in the anode. Moreover, the low angle boundaries were the fast diffusion channel of Cu atoms while the high grain boundaries in the range of 55°-65° were not favorable to the fast diffusion of Cu atoms.

Improving the -3 dB bandwidth of micro-size LEDs through p-electrode patterns for visible light communication.

We systematically studied the effect of p-electrode patterns on the optical properties and -3dB bandwidth of micro-size LEDs. The current spreading distribution can be effectively improved via adjusting the number and shape of the p-electrode branch, thus increasing the injection saturation current density and decreasing the series resistance. Compared with the micro-size LED using a disk p-electrode, the saturation light output power and -3dB bandwidth of the micro-size LED using a six-branches spiral p-electrode increase by 39.48% and 76.61%, respectively. Such a p-electrode pattern is a promising solution for micro-size LED applications in both illumination and visible light communication systems.

Microstructure and Grain Orientation Evolution in SnPb/SnAgCu Interconnects Under Electrical Current Stressing at Cryogenic Temperature.

Electromigration was characterized at the cathode Cu/solder interface-without the effect of Joule heating-by employing scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) analyses. Rapid (Cux,Ni1-x)6Sn5 intermetallic compound (IMC) growth was observed at the anomalous region at the cathode end due to the effect of current crowding. The abnormal isotropic diffusion and parallel distribution of Pb were characterized in an ultra-low temperature environment in a monocrystalline structure stressed at -196 °C. The interesting results were attributed to crystallographic transformation due to the simultaneous effect of cryogenic and electrical stressing. The diffusion behavior of Pb atoms in face-centered cubic lattices performed isomorphism. As a result, Pb atoms of the bump gathered at the high-energy grain boundaries by diffusing through the face-centered cubic lattices around the long grain boundary, eventually forming a long-range distribution and accumulation of Pb elements. Our study may provide understanding of cryogenic electromigration evolution of the Cu/solder interface and provide visual data for abnormal lattice transformation at the current stressing.

Contrast Enhancement by Nonlinear Diffusion Filtering.

To enhance the visual quality of an image that is degraded by uneven light, an effective method is to estimate the illumination component and compress it. Some previous methods have either defects of halo artifacts or contrast loss in the enhanced image due to incorrect estimation. In this paper, we discuss this problem and propose a novel method to estimate the illumination. The illumination is obtained by iteratively solving a nonlinear diffusion equation. During the diffusion process, surround suppression is embedded in the conductance function to specially enhance the diffusive strength in textural areas of the image. The proposed estimation method has the following two merits: 1) the boundary areas are preserved in the illumination, and thus halo artifacts are prevented and 2) the textural details are preserved in the reflectance to not suffer from illumination compression, which contributes to the contrast enhancement in the result. Experimental results show that the proposed algorithm achieves excellent performance in artifact removal and local contrast enhancement.