Co-doped NaYF 4 :Yb/Er/Tm upconversion luminescent coating to enhance the efficiency of photovoltaic cells.

The use of upconversion luminescent materials to broaden the utilization range of the solar spectrum to enhance the efficiency of photovoltaic cells offers a promising and sustainable approach. However, the low luminescence intensity and easy quenching of upconversion luminescent materials bring serious challenges to the practical application. Herein, a novel method using Co 2+ ion doping to regulate the luminescence properties of NaYF 4 :Yb/Er/Tm is proposed. NaYF 4 :Yb/Er/Tm microcrystals doped with different proportions of Co 2+ ions are prepared and used as coatings on the surface of photovoltaic cells. Co 2+ ions regulate the crystallinity and size of the NaYF 4 :Yb/Er/Tm microcrystals and reduce the crystal field symmetry of the activator (Er 3+ and Tm 3+ ) ions. The results show that the emission intensity of green and red light is 18.19% and 83.24% times higher than that of undoped Co 2+ ion materials, respectively. Besides, the efficiency of photovoltaic cells after coating Co 2+ ion doped NaYF 4 :Yb/Er/Tm is 2.08% higher than that of the uncoated one. This work underscores the importance of Co 2+ ion doping to improve and enhance the luminescence properties of NaYF 4 :Yb/Er/Tm, to further enhance the efficiency of photovoltaic cells.