Given the abundance and nontoxicity of silicon (Si) and their compatibility with conventional Si technologies, Si nanocrystals (NCs) hold great promise to improve existing Si-based technologies and advance the use of Si toward new fields such as wearable and biointegrable electronics. We have recently found that heavy boron (B) doping causes the surface region of Si NCs to be negatively charged. The resulting electrostatic effect enables the ready formation of stable B-doped Si-NC colloids. High-performance photodetectors and synaptic devices have been fabricated by using these colloids to take advantage of the novel optical properties (e. g., broadband absorption and localized surface plasmon resonance) of B-doped Si NCs. In addition, we have fabricated a series of high-performance near-infrared light-emitting diodes based on Si NCs by either engineering the ligands at the NC surface or incorporating functional interlayers into the device structures.