Greenish yellow-emitting carbon dot-based films for luminescent solar concentrator applications

Abstract

Currently, most carbon dots (CDs) are synthesized from carbon-based materials in autoclaves with high pressure, and then applied in various fields. This work explored the facile synthesis of CDs at atmospheric pressure, which were then purified and embedded in the ethylene-vinyl acetate (EVA) copolymer to form CDs@EVA films and applied in luminescent solar concentrator (LSC) devices. First, crude CDs were synthesized by refluxing p-phenylenediamine (p-PD) in diphenyl ether at 250 °C for 2 h under ambient air conditions, followed by purification using silica gel column chromatography to obtain purified CDs with a photoluminescence (PL) quantum yield of 56% and an average particle size of 15.1 ± 4.4 nm. The CDs@EVA films were fabricated at CD concentrations of 0.05 wt%, 0.10 wt%, and 0.15 wt%, and their thickness was varied from ∼100 μm to ∼500 μm. The yellowish-transparent CDs@EVA films exhibited greenish-yellow emission with absorption peaks at 350 nm and 470 nm, corresponding to the n–π* transition of CN bonds and the π–π* transition between the highest occupied molecular orbital and the lowest unoccupied molecular orbital of π-conjugated electrons. The PL intensity reached its maximum at 0.05 wt% CD concentration and 408 μm thickness due to self-absorption of emission from CDs. According to the current–voltage curve measurements under AM1.5G simulated sunlight, this film exhibited the maximum short-circuit current (I_sc) and power conversion efficiency (η) of the LSC device. Additionally, incident photon-to-current efficiency spectrum measurements revealed that the enhanced I_sc and η in CDs@EVA films mainly resulted from emission by absorption through the n–π* and π–π* transitions.