• Energy Research

Due to its low cost and high possibilities, multicrystalline silicon (mc-Si) is an attractive substrate to produce solar cells. Trying to reach high efficiencies with a simple and repetitive method, we adapted a standard monocrystalline process to multicrystalline material. Different gettering methods (Phosphorous, Aluminium and P and Al co-gettering) have been studied. In our laboratory, 15.2% efficiency have been achieved to date. PC1D simulations shows that, with a reduction of bulk recombination and a better front and rear passivation schemes, efficiencies higher than 18% could be obtained.

The influence of the relative position of Ag metallic nanoparticles (Ag MNPs) embedded in a 100 nm SiOx 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 SiOx ARC. This has been done for different sizes of Ag nanoparticles. An alternative for PECVD to encapsulate Ag MNPs with SiOx 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.

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.