Photovoltaic Applications of Silicon Nanocrystal Based Nanostructures Induced by Nanosecond Laser Fragmentation in Liquid Media

Abstract

Silicon nanocrystals (Si-ncs) with quantum confinement properties represent an attractive photovoltaic material. The ability to collect the photogenerated current through efficient electronic transport and exciton dissociation is a current challenge for the deployment of Si-nc based solar cells. We report here on prospective and cost-effective approaches to engineer the surface of electrochemically etched Si-ncs by laser fragmentation in ethanol and water. The properties of the engineered Si-ncs have been analyzed in detail by photoluminescence and absorption measurements together with Fourier transform infrared spectroscopy. To demonstrate the advantageous attributes of Si-nc surface engineering in liquid media, a few photovoltaic devices based on different architectures have been fabricated. First, anatase TiO2 nanotubes have been used as a host template for laser-fragmented Si-ncs to form inorganic-sensitized solar cell architectures. Second, we have produced bulk-heterojunction solar cells with a Si-nc/fullerene photoactive interface. This design has been further improved by functionalizing the Si-nc surface with water-soluble poly(3,4-ethylenedioxythiophene), i.e., PEDOT. All the devices produced here have been characterized with external quantum efficiency measurements, and in some cases the current−voltage characteristic has been also measured.

Synthesis and surface engineering of nanomaterials by atmospheric-pressure microplasmas

“…Si-NPs have then been collected and exposed to air at ambient conditions for about 24 hours. It has been shown previously that the conditions of the electrochemically etched Si-NPs powder are stable in air [37]. The Si-NPs (2.5 mg) have then been added to 5 mL of water, however due to the hydrogen terminations, the Si-NPs are highly hydrophobic and do not disperse in water remaining at the waterair interface (figure 8a).…”

“…NPs made of silicon (Si-NPs) that exhibit quantum confinement properties (< 10 nm diameter) have become very attractive for optoelectronic conversion and particularly for photovoltaic applications [36,37]. Si-NPs also present many advantages that include low toxicity, abundance in nature and possibility of carrier multiplication [38,39].…”

“…[41,43]), Si-NPs can be derived from porous silicon: Canham et al [44] discovered in 1990 that porous silicon, which consists of nano-scale crystalline particles, exhibits efficient photoluminescence (PL) at visible wavelengths. After this discovery there has been a considerable amount of research for the development of Si-NPs and their integration in application devices [36,37]. However, a few basic challenges still need to be resolved to make Si-NPs functional elements for efficient opto-electronic conversion; in particular an in-depth understanding and control of Si-NPS surface characteristics is of paramount importance.…”

“…However, a few basic challenges still need to be resolved to make Si-NPs functional elements for efficient opto-electronic conversion; in particular an in-depth understanding and control of Si-NPS surface characteristics is of paramount importance. Surface terminations have a drastic impact on the excitonic dissociation, carrier transfer and energy band gap [37,45,46]. Furthermore, the surface of the Si-NPs determines their processability in liquid solution which is very important for low-cost fabrication techniques (e.g.…”

“…screen printing) of solar cells. Recently Švrček et al has shown the possibility of Si-NPs surface engineering by AMP processing or by laser fragmentation in liquid [5,37]. Specifically, laser fragmentation in water has proved that the hydrophobic character of SiNPs can be changed to hydrophilic [37] and this is thanks to induced surface chemistry in the laser-based process.…”