Efficiency improvement of silicon nanostructure-based solar cells.

Solar cells based on a high-efficiency silicon nanostructure (SNS) were developed using a two-step metal-assisted electroless etching (MAEE) technique, phosphorus silicate glass (PSG) doping and screen printing. This process was used to produce solar cells with a silver nitrate (AgNO3) etching solution in different concentrations. Compared to cells produced using the single MAEE technique, SNS-based solar cells produced with the two-step MAEE technique showed an increase in silicon surface coverage of ~181.1% and a decrease in reflectivity of ~144.3%. The performance of the SNS-based solar cells was found to be optimized (~11.86%) in an SNS with a length of ~300 nm, an aspect ratio of ~5, surface coverage of ~84.9% and a reflectivity of ~6.1%. The ~16.8% increase in power conversion efficiency (PCE) for the SNS-based solar cell indicates good potential for mass production.

Rice-straw-like structure of silicon nanowire arrays for a hydrogen gas sensor.

A rice-straw-like silicon nanowire (SiNW) array was developed for hydrogen gas sensing applications. The straight-aligned SiNW array sensor was first fabricated by the metal-assisted electroless etching (MAEE) technique. Rice-straw-like SiNW arrays were formed using a repeated MAEE technique. Hydrogen sensing characteristics were measured for gas concentrations from 20 to 1000 ppm at room temperature. The rice-straw-like SiNW-array-based hydrogen gas sensor performed with low noise and a high response (232.5%) for 1000 ppm hydrogen gas. It was found that the rice-straw-like SiNW-array hydrogen gas sensor had a much better response (approximately 2.5 times) than the straight-aligned SiNW-array sensor. The rice-straw-like SiNW-array structure effectively increased the surface area and the concentration of silicon oxide, which provided additional binding sites for gas molecules. Thus, the rice-straw-like SiNW-array-based hydrogen gas sensor possessed good sensing properties and has the potential for mass production of sensing devices.

Gas ionization sensors with carbon nanotube/nickel field emitters.

Gas ionization sensors based on the field emission properties of the carbon nanotube/nickel (CNT/Ni) field emitters were first developed in this work. It is found that the breakdown electric field (E(b)) slightly decreases from 2.2 V/microm to 1.9 V/microm as the pressure of H2 gas increases from 0.5 Torr to 100 Torr. On the contrary, E(b) obviously increases from 2.9 V/microm to 6.5 V/microm as O2 gas pressure increases from 0.5 Torr to 100 Torr. This may be explained by the depression of the electron emission that caused by the adsorption of the O2 gas on the CNT emitters. The Raman spectra of the CNT/Ni emitters also show that more defects were generated on the CNTs after O2 gas sensing. The Joule heating effect under high current density as performing H2 sensing was also observed. These effects may contribute the pressure dependence on the breakdown electric field of the CNT/Ni gas ionization sensors.