Application of β-NaYF₄:Er³⁺ (2%), Yb³⁺ (18%) up-conversion nanoparticles in polymer solar cells and its working mechanism

Oil-soluble and water-soluble β-NaYF₄:Er³⁺ (2%), Yb³⁺ (18%) up-conversion nanoparticles are respectively synthesized and incorporated into the poly(3,4-ethylenedioxythiophene) with poly(4-styrenesulfonate) hole extraction layer in poly(3-hexylthiophene)-based bulk heterojunction organic photovoltaic cells. The organic photovoltaic cells incorporated with water-soluble up-conversion nanoparticles exhibit higher enhancement factors of 9.9% and 8.2% for short-circuit current density and power conversion efficiency over the control devices, compared to 8.9% and 6.5% in oil-soluble nanoparticles-incorporated OPVs. The investigation on the up-conversion nanoparticles' emission, scattering, and resolvent revealed that nanoparticles' photoluminescence contribute little to device performance enhancement. In contrast, the main impact factors on performance enhancement include nanoparticle's resolvent, scattering, the nanoparticles-induced roughness and electrical conductivity change of hole extraction layer. The higher performances in 70 nm nanoparticles-incorporated photovoltaic cells are mainly attributed to a larger scattering, the rougher surface of hole extraction layer and a negligibly negative effect of the ethanol resolvent.