Nanofabrication processes for innovative nanohole-based solar cells

Abstract

The ability to form ordered nanostructures at the wafer level with low cost methodologies has represented a challenge in the last decade in many research fields spanning from nanoelectronics to photovoltaics (PVs). For the latter application the nanostructures have demonstrated interesting capabilities for exploiting the quantum effects in terms of efficient visible light absorption. To fabricate ordered nanostructures many solutions have been proposed but they provide feature densities lower than 109 cm−2 or present high fabrication costs. We propose a wafer level and low-cost Lithography based on block CoPolymers self-assembling (LCP), which allows the formation of nanofeatures controlled down to 10 nm and density higher than 5 × 1010 cm−2. We propose to use this technique to form radial junctions in nanoholes for solar cells. The approach is similar to that of the nanowires, i.e., it decouples the optical path of the visible photons from the electrical path of the carriers, but since the one-dimensional (1D) structures are embedded inside the bulk of the wafer the structure is more robust and allows easier implementation. To form the junction inside the nanoholes a novel strategy based on the deposition of monolayers of dopant-containing molecules is proposed. This technique allows to obtain shallow and controlled junction depths with peak carrier concentrations of about 1019 cm−3 for both n- and p-type doping.