Spectral Design of Light-emitting Diodes for Plant Photosynthesis Based on Quantum Dots

Light is one of the five indispensable factors for plant growth. Green houses and plant factories have advantages of growing vegetables off-season and high production. However, artificial lighting occupies most of the running cost during the operation of plant factories, and intelligent and programmable light-emitting diodes (LEDs) have been considered to be used as growing lamps to save energy. Taking both the photosynthetic and the visual performances into consideration, luminescent spectrum of LEDs based on quantum dot (QD) materials is designed and optimized according to the photosynthetic action spectrum (PAS) of plants. In our calculation, the three-band QD-based LEDs (QLEDs) show a highest photosynthetic action factor (PAF) of 8.088 and a highest induced photosynthetic index (IPI) of 4.012. The four-band QLEDs show a highest PAF of 7.689 and a highest IPI of 3.818. CdZnS/ZnS and CdZnS/ZnSe QDs are also synthesized for fabricating three- and four-band QLEDs. Investigations of the photosynthetic and the vison performances on these devices are consistent with those theoretical simulation results. Both the simulation and the experimental results show that either the three- or the four-band QLEDs has better photosynthetic parameters than those of the conventional light sources. The fabricated four-band QLED under different applied current exhibits a highest PAF of 2.6942 and a highest IPI of 1.3621. For the vison performances, the four-band device demonstrate a highest CRI of 93 and a highest CCT of 2053 K. Despite the visual performances of the four-band QLEDs show improvement than those of the three-band ones, they still need to be improved to offer better visual experience for human eyes. With further investigation on the synthesis of emission tunable QD materials and the optimization of the spectrum, highly efficient QLEDs with both good photosynthetic and visual performances are expected to be applied in the field of growing lamps.