Low-Temperature Annealing for Highly Conductive Lead Chalcogenide Quantum Dot Solids

Electrical conductivity in quantum dot solids is crucial for application in devices. In addition to the well-known ligand exchange strategies for enhanced conductivity, the current study examined the optical, structural, and electrical properties of ethanedithiol-treated layer-by-layer (LbL) assembled quantum dot solid (QDS) films following low-temperature annealing (room temperature to 170 degrees C). As the annealing temperature increased, it was induced that the average separation between nanocrystal quantum dots is decreased, and accordingly, the overall conductivity of the QDS increased exponentially. From a simplified percolation model, the activation energy of temperature-dependent quantum dot attachment was estimated to be around 0.26-0.27 eV both for PbS and PbSe quantum dot solids. Furthermore, the results of this study indicated that device applications requiring higher conductivity, attainable through high-temperature annealing, may also require repassivation after annealing.