Si-nanosponge embedded in SiO2 as a new absorber material for photovoltaics

Silicon based nanostructures became within the last years most promising material for the PV market. Quantum confinement effect of nanostructured silicon allows for band gap engineering just by size manipulation to absorb the light in more efficient way.
Here, we consider SiOx layers fabricated by magnetron co-sputter deposition, which after thermal treatment decompose into a network of Si nanowires embedded in SiO2. The thermally activated spinodal decomposition is performed by rapid thermal processing within a few seconds and by very rapid thermal processing within several ms using diode laser. The morphology and crystallinity of the Si-nanosponge was measured by energy filtered TEM and Raman, respectively. The details of decomposition are studied using the atomistic kinetic Monte-Carlo (KMC) simulations at different concentrations defined by the x parameter. The spatiotemporal temperature profiles T(x, t) of the scanned laser has been calculated as a function of thickness and time by the heat transport equation. The obtained profiles are used in the KMC. The combined theoretical and experimental investigations support the band gap engineering of the Si-nanosponge absorber via a control of the quantum confinement.