. Intense visible emission from the controlled defects in ZnO nanoparticles for energy down-shifting applications in solar cells
Résumé
Zinc oxide nanoparticles (NPs) have aroused an increasing interest for their potential application in the white light sources and as energy conversion material due to the variety of intrinsic defects which permit to generate a wide emission spectrum from the blue to the IR range. However, the origin of these emissions remains still unclear and the precise control of the defects quantity is a challenging task. Because of the easy and adjustable synthesis condition, sol-gel methods have been applied to synthesize ZnO NPs. The nanoparticle size, morphology, crystalline quality and the zeta potential have been controlled via the modification of the synthesis parameters (the nature of solvent, the presence of the additives and of the surfactants and the reaction time). Since all these synthesis parameters play a major role in the introduction of defects into the structure of ZnO NPs, the defect emission spectrum range and the luminescent efficiency can be controlled. The intense visible emission with a luminescent external quantum efficiency (EQE) of more than 50 % (and up to 70 %) was attained by controlling the crystalline order of ZnO NPs. The hydroxyl group present on the surface of the ZnO NPs turned out to influence their crystalline quality and dispersibility. The influence of ZnO NPs used as energy down-shifting layer on the efficiency of various types of solar cells is also presented.