This paper presents an experimental study of the variation in the performance of silicon solar cells with temperature. The cells studied were fabricated from standard electronic grade and upgraded metallurgical grade silicon. Both monocrystalline and multicrystalline silicon wafers are included. The main object is to evaluate critical cell parameters for cell performance against temperature. The critical parameters selected are the wafer type, wafer resistivity, fabrication process routing, and solar cell electrical parameters. Their impact on cell performance is evaluated by systematic study expressed in terms of temperature coefficients. The resulting quantitative study finds different cell performance sensitivities to specific parameters: the crystal growth, the use of electronic grade or upgraded metallurgical grade silicon wafers, and the fabrication process employed. It is shown that the temperature coefficient of the short circuit current is an important factor in the tendency of the temperature coefficient of the maximum power. This phenomenon is responsible for the superior temperature coefficient observed in solar cells fabricated from upgraded metallurgical grade silicon wafers. Furthermore, the study quantitatively demonstrates the sensitivity of cell temperature coefficient to fabrication process. The optimum process for a superior temperature coefficient is identified, and also corresponds to an improved overall efficiency

Porous silicon seems to be an appropriate material platform for the development of high-sensitivity and low-cost optical sensors, as their porous nature increases the interaction with the target substances, and their fabrication process is very simple and inexpensive. In this paper, we present the experimental development of a porous silicon microcavity sensor and its use for real-time in-flow sensing application. A high-sensitivity configuration was designed and then fabricated, by electrochemically etching a silicon wafer. Refractive index sensing experiments were realized by flowing several dilutions with decreasing refractive indices, and measuring the spectral shift in real-time. The porous silicon microcavity sensor showed a very linear response over a wide refractive index range, with a sensitivity around 1000 nm/refractive index unit (RIU), which allowed us to directly detect refractive index variations in the 10⁻⁷ RIU range.

A highly sensitive photonic sensor based on a porous silicon ring resonator was developed and experimentally characterized. The photonic sensing structure was fabricated by exploiting a porous silicon double layer, where the top layer of a low porosity was used to form photonic elements by e-beam lithography and the bottom layer of a high porosity was used to confine light in the vertical direction. The sensing performance of the ring resonator sensor based on porous silicon was compared for the different resonances within the analyzed wavelength range both for transverse-electric and transverse-magnetic polarizations. We determined that a sensitivity up to 439 nm/RIU for low refractive index changes can be achieved depending on the optical field distribution given by each resonance/polarization.

The influence of the relative position of Ag metallic nanoparticles (Ag MNPs) embedded in a 100 nm SiO_x Antireflection Coating (ARC) for specular polished c-Si substrates is studied. It is demonstrated that this Plasmonic ARC (PARC) can achieve lower average reflectivities than the optimised SiO_x ARC. This has been done for different sizes of Ag nanoparticles. An alternative for PECVD to encapsulate Ag MNPs with SiO_x is presented, avoiding the risk of metallic contamination in the reactor chamber as well as its effect on the size and shape of the self-aggregated Ag MNP. It is demonstrated, however, that this PARC is not suitable for silicon solar cells as a substitute for traditional ARC because it presents a high loss related with Fano destructive interference.

Porous materials have become ideal candidates for the creation of optical sensors that are able to reach extremely high sensitivities, due to both the possibility to infiltrate the target substances on them and to their large surface-to-volume ratio. In this work, we present a new alternative for the creation of porous optical sensors based on the use of polymeric nanofibers (NFs) layers fabricated by electrospinning. Polyamide 6 (PA6) NFs layers with average diameters lower than 30 nm and high porosities have been used for the creation of Fabry-Pérot optical sensing structures, which have shown an experimental sensitivity up to 1060 nm/RIU (refractive index unit). This high sensitivity, together with the low production cost and the possibility to be manufactured over large areas, make NFs-based structures a very promising candidate for the development of low-cost and high performance optical sensors.