Andres Velarde1 Hunter McDaniel1 Matt Bergren1 Nikolay Makarov1 Karthik Ramasamy1 Aaron Jackson1

1, UbiQD, Los Alamos, New Mexico, United States

The development of highly photoluminescent, copper-indium-sulfide (CIS) quantum dots (QD) has broadened the scope of QD applications owing to their lowered toxicity and reduced manufacturing costs. Recent efforts by UbiQD, the leading manufacturer of low-cost CIS QDs, have been focused toward the development of robust and efficient luminescent solar concentrator (LSC) technology. The key material for LSC technology is a QD-polymer nanocomposite (PNC) with no scattering and/or surface defects. In developing PNCs at UbiQD, acrylate polymers made via cast-in-place methods have the best performance. The primary challenge for optimizing acrylate PNCs for use as LSCs lies in the dispersion of QDs in monomer and the subsequent polymerization of the material while maintaining dispersion. Ample consideration must be given to a number of nanocomposite production variables including (i) choice of monomer, (ii) method of polymerization, and (iii) nanoparticle surface chemistry. Depending on the monomer choice, the glass transition temperature and shrinkage behavior upon polymerization can vary from material to material, thus dictating the surface properties of the resultant PNC. With regard to the method of polymerization, there exist a number of trade-offs between polymerization by exposure to ultraviolet light versus heat. Most notable are the differences in speed and cost between the two methods. UV light polymerization can significantly reduce PNC manufacturing time making it an ideal method for large scale polymer curing; however, absorption of UV light by the quantum dots can slow polymerization and damage the QDs. While thermal polymerization is superior in preserving the optical properties of the QDs and may be cheaper to implement than UV exposure systems, it can prove a costly method of PNC manufacturing at larger scales owing to substantially longer material processing times. Finally, the surface chemistry of the QDs controls, to a great extent, the solubility of the nanoparticles in monomer and polymer. We demonstrate that additives and native ligand modification are potential strategies for improving dispersion.
UbiQD’s QDs have been shown to exhibit PLQY up to 95%, enabling highly efficient energy conversion. When incorporated into polymers, we maintain up to 8% external quantum efficiency at 60% transmittance, the highest external quantum efficiency reported for LSC technology with polymer sheets to our knowledge.