Colloidal heavily doped silicon nanocrystals (Si NCs) exhibiting tunable localized surface plasmon resonance (LSPR) are of great interest in cost-effective, solution-processed optoelectronic devices given the abundance and nontoxicity of Si. In this work we show that tunable plasmonic properties and colloidal stability without the use of ligands can be simultaneously obtained for Si NCs heavily doped with boron (B). The heavily B-doped Si NC colloids are found to be stable in air for months, opening up the possibility of device processing in ambient atmosphere. The optical absorption of heavily B-doped Si NCs reveals that the heavy B doping not only changes the concentration of free carriers that are confined in Si NCs but also modifies the band structure of Si NCs. After heavy B doping both indirect and direct electronic transition energies remarkably decrease in Si NCs because the heavy B doping induced movement of the conduction band toward the band gap could be more significant than that of the Fermi level into the valence band. The LSPR of heavily B-doped Si NCs originates from free holes above the Fermi level, which are largely from the B-induced impurity band.

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Current researches on silicon nanoparticles (Si NPs) are mainly focusing on the crystallized one, while some basic optical and electrical properties of particles with different crystallinities are still unclear. Hence, in this work, Si NPs with different crystallinities were easily fabricated with non-thermal plasma by changing the input power, and the crystallinity effects on the optical, electrical, and photovoltaic properties of particles were extensively studied. It is found that amorphous particles have strong light absorption, especially in short wavelength region; however, the carrier mobility is relatively poor. This is mainly because of numerous dangling bonds and defects that exist in Si NPs with poor crystallinity, which work as carrier trapping centers. As a result, the efficiency of Si NPs-based hybrid solar cells increases monotonously with particle crystallinity. This indicates that highly crystallized Si nanocrystals with less defects are desirable for high efficiency solar cells.

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