Systematic Characterization of Silicon Nanodot Absorption for Third Generation Photovoltaics

Aim of this work is the determination of the optical parameters of silicon nanocrystals (nc-Si) in Silicon Rich Carbide (SRC) matrix and in particular of the absorption coefficient of the material, essential in the design of photovoltaic devices. The nanocrystals were formed using the superlattice SRC/SiC approach followed by annealing. The optical properties of the superlattices after annealing up to 1100 °C are investigated. Severe shrinkage of the materials is observed, more marked for higher carbon concentration. Contrary to the case of Silicon Rich Oxide (SRO) matrix, the simulation of R&T spectra based on EMA modeling shows that the material can be described by a mixture of crystallized SiC, crystallized Si, and amorphous Si. Larger Si concentration in the SRC layer leads to larger crystallized fraction. The differences with the SRO case are illustrated and discussed. The results are applied to the optical simulation of a hypothetical tandem device. It is obtained that much thinner absorbers could be used in the SRC case with respect to SRO one.