Perspectives on metal induced crystallization of a-Si and a-Ge thin films

In recent times, the metal induced crystallization (MIC) process in amorphous semiconductors (a-Si and a-Ge) has been extensively investigated by many researchers due to potential applications of crystalline semiconductors in high-density data storage devices, flat panel displays, and high performance solar cells. In this context, we have presented a review on different schemes of MIC in metal/a-Si and metal/a-Ge bilayer films (with stacking change) on various substrates under different annealing conditions. The parameters, which limit crystallization of a-Si and a-Ge have been analyzed and discussed extensively keeping in mind their applications in solar cells and flat panel displays. The MIC of a-Si and a-Ge films under ion beam irradiation has also been discussed in detail. At the end, some suggestions to overcome the limitations of the MIC process in producing better crystalline semiconductors have been proposed. We believe that this review article will inspire readers to perform a thorough investigation on various aspects of MIC for further development of high efficiency solar cells and high quality flat panel displays.

High Electrochemical Performance Silicon Thin-Film Free-Standing Electrodes Based on Buckypaper for Flexible Lithium-Ion Batteries

Recently, applications for lithium-ion batteries (LIBs) have expanded to include electric vehicles and electric energy storage systems, extending beyond power sources for portable electronic devices. The power sources of these flexible electronic devices require the creation of thin, light, and flexible power supply devices such as flexile electrolytes/insulators, electrode materials, current collectors, and batteries that play an important role in packaging. Demand will require the progress of modern electrode materials with high capacity, rate capability, cycle stability, electrical conductivity, and mechanical flexibility for the time to come. The integration of high electrical conductivity and flexible buckypaper (oxidized Multi-walled carbon nanotubes (MWCNTs) film) and high theoretical capacity silicon materials are effective for obtaining superior high-energy-density and flexible electrode materials. Therefore, this study focuses on improving the high-capacity, capability-cycling stability of the thin-film Si buckypaper free-standing electrodes for lightweight and flexible energy-supply devices. First, buckypaper (oxidized MWCNTs) was prepared by assembling a free stand-alone electrode, and electrical conductivity tests confirmed that the buckypaper has sufficient electrical conductivity (10-4(S m-1) in LIBs) to operate simultaneously with a current collector. Subsequently, silicon was deposited on the buckypaper via magnetron sputtering. Next, the thin-film Si buckypaper freestanding electrodes were heat-treated at 600 °C in a vacuum, which improved their electrochemical performance significantly. Electrochemical results demonstrated that the electrode capacity can be increased by 27/26 and 95/93 μAh in unheated and heated buckypaper current collectors, respectively. The measured discharge/charge capacities of the USi_HBP electrode were 108/106 μAh after 100 cycles, corresponding to a Coulombic efficiency of 98.1%, whereas the HSi_HBP electrode indicated a discharge/charge capacity of 193/192 μAh at the 100th cycle, corresponding to a capacity retention of 99.5%. In particular, the HSi_HBP electrode can decrease the capacity by less than 1.5% compared with the value of the first cycle after 100 cycles, demonstrating excellent electrochemical stability.

Three-dimensional radial junction solar cell based on ordered silicon nanowires

Highly ordered silicon nanowires (SiNWs) were fabricated by nanoimprint lithography and Bosch etching methods. A polycrystalline silicon shell was grown to form a radial p-n junction. To enhance its anti-reflection properties and conductivity, a thin ITO layer was deposited on the SiNWs solar cell, then a micro-grid electrode was introduced to minimize the metal areas to maximize carrier collection. Finally, shorter nanowires were used to reduce surface recombination and achieve an efficiency of 10.5%. This work is expected to show some possible techniques to improve the performance of silicon nanostructure solar cell.

Effect of annealing time on aluminum-induced crystallization of silicon suboxide thin films

Polycrystalline silicon (poly-Si) thin films were obtained by aluminium induced crystallisation of amorphous silicon suboxide (a-SiOx, x = 0.22) via annealing of a-SiO0.22/Al bilayer structures at 550 °C for 4 - 30 h. The a-SiO0.22/Al thickness ratio was approximately 1. According optical microscopy measurements, the crystallized fraction reached the saturation value of 85% after annealing for 20 h. The further increase in the annealing time didn’t lead to an increase in this value. X-ray diffraction measurements revealed that the formed poly-Si had a strong Si (111) preferred orientation.