Hybrid ZnO mesospheres for white LED and photovoltaic markets
Résumé
An overwhelming economic improvement for white LED and photovoltaic (PV) markets is based on the use of lanthanide-free phosphors that are supposed to convert UV light into visible one, thanks to down-conversion (DS) process. ZnO nanoparticles (NPs) have aroused an increasing interest since they possess a variety of intrinsic defects that provide light emission in the visible range without the introduction of any additional impurity. However, high photoluminescent quantum yield (PLQY), stable green/yellow emission and easy scale–up process are expected for industrial applications. Li-doping and polymer surface modifications of ZnO nanoparticles are mainly used in order to reach high PLQY (> 30 %) but PLQY decay over few days, uses of sophisticated polymers or multi-step reactions are the main issues for industrial implementation. In collaboration with the company Lotus Synthesis, we developped and patented an industry-capable and cost effective chemical solution process to get unique mesospheric self-assembly hybrid ZnO system with intense (PLQY = 40-75 %) and stable visible emissions. We also demonstrate that the use of mixture of commercial polyacrylic acid-based polymers can provide large scale amounts of ZnO NPs clear water suspensions that can be dried and dispersed again in water without compromising the functional performance (e.g. transparency and PLQY) of the final DS layer. We will then address the effects of the ZnO NPs surface functionalization - such as nature, molecular weight, concentration, ratio of the PAA-based polymers and self-assembly process- on the enhancement of the efficiency of DS hybrid materials for LED and PV markets (or even cosmetics one).