Silicon nanocrystals produced by solid phase crystallisation of superlattices for photovoltaic applications

Silicon nanocrystals in a dielectric matrix can form a material with higher band gap than that of bulk crystalline silicon and can therefore be applied as stable top solar cells for an all-silicon based tandem solar cell. In this review article we focus on one proven method to fabricate such structures, the superlattice approach, as cost-efficiency seems to be possible which is essential for photovoltaic applications. We comprehensively discuss the different challenges for competing material systems such as SiO2, Si3N4 and SiC and give an overview on what is known so far in terms of electro-optical performance of the materials. So far, devices using silicon nanocrystals have been realised either on silicon wafers, or using in-situ doping in the superlattice deposition which may hinder the nanocrystal formation. Nevertheless, Voc of up to 518 mV has been shown on such devices. In this paper we also present a membrane structure which allows the investigation of the electrical and photovoltaic properties of nanocrystal quantum dot layers independently from the substrate and unaffected by dopant diffusion. The device structure provides full flexibility in the material choice of both, i.e. electron and hole, contacts.