Mohammad Javadi BalakanMJ Balakan

Graphene lets light pass into the silicon beneath it, which makes graphene–silicon junctions attractive for solar cells and detectors. We showed that charge crossing this 2D/3D interface is limited by how slowly electrons leave the graphene plane, and calculated the efficiency limit of graphene–silicon solar cells. We also grew borophene, a one-atom-thick metal, by chemical vapor deposition, a scalable route to 2D interconnects.

• 10⁶×slower charge transfer than gold–silicon Schottky contacts
• 25.5%efficiency limit of graphene/silicon solar cells
• FirstCVD growth of borophene

Coating silicon with a conductive polymer gives junctions that are made at low temperature from solution and work over large areas. We worked out how charge moves through them, injection over an interface barrier in one direction and space-charge-limited flow through the polymer in the other. On this platform we built position-sensitive detectors and self-powered photodiodes that stay stable after long exposure to air.

• >100 mV/mmposition sensitivity (APL Editor's Pick)
• 10⁶ V/Wphotovoltage responsivity with pW-level noise

Our Monte Carlo simulations showed that confining a porous oxide network steers electrons toward the collecting electrode. We then built column-structured dye-sensitized solar cells and measured longer electron lifetimes and diffusion lengths. With COMSOL and numerical models, we also explained how plasma-enhanced CVD produces self-organized, single-standing carbon nanotubes.

• ~3×longer electron diffusion length in patterned TiO₂
• 10⁵×better detection of faint UV light