Low-Cost Post-Growth Treatments of Crystalline Silicon Nanoparticles Improving Surface and Electronic Properties

Freestanding silicon nanocrystals (Si-ncs) offer unique optical and electronic properties for new photovoltaic, thermoelectric, and other electronic devices. A method to fabricate Si-ncs which is scalable to industrial usage has been developed in recent years. However, barriers to the widespread utilization of these nanocrystals are the presence of charge-trapping defects and an oxide shell formed upon ambient atmosphere exposure hindering the charge transport. Here, we exploit low-cost post-growth treatment routes based on wet-etching in hydrofluoric acid plus surface hydrosilylation or annealing enabling a complete native oxide removal and a reduction of the defect density by up to two orders of magnitude. Moreover, when compared with only H-terminated Si-ncs we report an enhancement of the conductivity by up to a factor of 400 for films of HF etched and annealed Si-ncs, which retain a defect density below that of untreated Si-ncs even after several months of air exposure. Further, we demonstrate that HF etched and hydrosilylated Si-ncs are extremely stable against oxidation and maintain a very low defect density after a long-term storage in air, opening the possibility of device processing in ambient atmosphere.