Production and Characterization of Silicon Nanoparticles for Photovoltaic Applications

Semiconductor nanocrystals (NCs) are relevant structures for the realisation of low-cost production and conversion efficiency increase in photovoltaic technology. The energy structure of silicon (Si) quantum dots is manipulated trough the quantum confinement effect of particle size reduction. As a result of nanocrystal size reduction the energy band gap of Si quantum dots is increased to match the solar spectrum. A promising concept in photovoltaic applications is the implementation of Si quantum dots in multi-junction photovoltaic cells. In multi-junction solar cells multiple semiconductors with different energy band gaps yield different parts of the solar spectrum. Fabrication of crystalline Si photovoltaic cells is beneficial for large-scale production because of the non-toxicity and abundant resource availability of silicon. The Si nanoparticles in this study are produced with the Oxford Applied Research NC200U nanocluster source. Size characterization of the Si nanoparticles is conducted with the experimental techniques of AFM and TEM. AFM results indicate the Si cluster size dependency on the functional parameters of the cluster source: applied power, aggregation length and gas flow rate. A TEM image of the Si nanoclusters displayed the crystalline hexagonal structure of silicon. Optimization of the cluster source parameters resulted in the formation of crystalline Si nanoparticles relevant to the quantum confinement regime of 4.9 nm. In addition, the Si nanoclusters were optically analyzed using UV-VIS and photoluminescent (PL) spectroscopy. Hydrogen (H2) and helium (He) addition to the argon (Ar) cluster source gas flow resulted in a higher sputtering yield, making layers of Si nanoclusters possible. The Si nanoparticles PL analysis was complicated by the strong substrate background. Due to the likely crystalline nature of the Si nanoclusters the emission spectra exhibited no measurable PL intensity peak below 1100 nm