Molecular Doping applied to Si Nanowires array based Solar Cells

Solution-based processing is a rapidly growing area in the electronics and photonics field due to the possibility of reducing fabrication costs of materials for solar cells, transistors, memory and many other devices. Moreover thanks to its intrinsic nature it provides the possibility to perform conformal processing on structured surfaces. Most of the solution-processing work has so far been devoted to organic materials, but in this work an approach focused on nanostructured silicon is presented. The idea consists in the immersion of a silicon wafer, with Si nanowires grown on top, in a chemical bath containing dopant precursors molecules diluted in a solvent. The molecules deposit from the liquid all over the exposed surfaces and work as a dopant source for the Si nanowires during successive thermal annealing. Doping levels of 1e19 cm-3 are controllably obtained without structural damage and hetero-interfaces creation. The Si-NWs array used presents density of 2e10 cm-2, average length of 500 nm and diameters up to 70 nm. The doped Si-NWs are then integrated in complete solar cells which have been electrically characterized. It is found that the molecular doping method applied to the SiNW arrays provides higher short circuit current and fill factor than the reference samples.