In this study, the surface passivation process for InP-based quantum dots (QDs) is investigated. Surface coating is performed with poly(methylmethacrylate) (PMMA) and thioglycolic acid. The quantum yield (QY) of a PMMA-coated sample slightly increases by approximately 1.3% relative to that of the as-synthesized InP/ZnS QDs. The QYs of the uncoated and PMMA-coated samples drastically decrease after 16 days because of the high defect state density of the InP-based QDs. PMMA does not have a significant effect on the defect passivation. Thioglycolic acid is investigated in this study for the effective surface passivation of InP-based QDs. Surface passivation with thioglycolic acid is more effective than that with the PMMA coating, and the QY increases from 1.7% to 11.3%. ZnS formed on the surface of the InP QDs and S in thioglycolic acid show strong bonding property. Additionally, the QY is further increased up to 21.0% by the photochemical reaction. Electron–hole pairs are formed by light irradiation and lead to strong bonding between the inorganic and thioglycolic acid sulfur. The surface of the InP core QDs, which does not emit light, is passivated by the irradiated light and emits green light after the photochemical reaction.

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• Poly(methylmethacrylate) coating on quantum dot surfaces via photo-chemical reaction for defect passivation
  Doyeon Kim, So-Yeong Joo, Chan Gi Lee, Bum-Sung Kim, Woo-Byoung Kim
  Journal of Photochemistry and Photobiology A: Chemistry.2019; 376: 206.     CrossRef

We have investigated the washing method of as-synthesized CdSe/ZnS core/shell structure quantum dots (QDs) and the effective surface passivation method of the washed QDs using PMMA. The quantum yield (QY%) of assynthesized QDs decreases with time, from 79.3% to 21.1%, owing to surface reaction with residual organics. The decreased QY% is restored to the QY% of as-synthesized QDs by washing. However, the QY% of washed QDs also decreases with time, owing to the absence of surface passivation layer. On the other hand, the PMMA-treated QDs maintained a relatively higher QY% after washing than that of the washed QDs that were kept in toluene solution for 30 days. Formation of the PMMA coating layer on CdSe/ZnS QD surface is confirmed by HR-TEM and FT-IR. It is found that the PMMA surface coating, when combined with washing, is useful to be applied in the storage of QDs, owing to its long-term stability.

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• Improvement of Short-Circuit Current of Quantum Dot Sensitive Solar Cell Through Various Size of Quantum Dots
  Seung Hwan Ji, Hye Won Yun, Jin Ho Lee, Bum-Sung Kim, Woo-Byoung Kim
  Korean Journal of Materials Research.2021; 31(1): 16.     CrossRef
• Poly(methylmethacrylate) coating on quantum dot surfaces via photo-chemical reaction for defect passivation
  Doyeon Kim, So-Yeong Joo, Chan Gi Lee, Bum-Sung Kim, Woo-Byoung Kim
  Journal of Photochemistry and Photobiology A: Chemistry.2019; 376: 206.     CrossRef
• Study on Surface-defect Passivation of InP System Quantum Dots by Photochemical Method
  Doyeon Kim, Hyun-Su Park, Hye Mi Cho, Bum-Sung Kim, Woo-Byoung Kim
  Journal of Korean Powder Metallurgy Institute.2017; 24(6): 489.     CrossRef