Effects of ligand exchanged CdSe quantum dot interlayer for inverted organic solar cells

• Mono-dispersed CdSe QDs is successfully synthesized from one-pot synthesis method.
• 3-MPA SAM treatment plays an important role of a uniform deposition of CdSe QDs layer.
• FT-IR, UV–Vis, TEM, and confocal microscope prove the ligand exchanged CdSe QDs.
• CdSe QDs capped with pyridine serve as electron transport layer from energy level analysis (UPS).
• Enhanced device electrical parameters are related to the increased shunt and decreased series resistance.

This research focuses on the effect of ligand exchanged CdSe quantum dots (QDs) interlayer to solve the self-aggregation, and applied to uniform coating of QDs in inverted organic solar cells. Because the oleic acid ligand has a tendency to act as an insulator, the ligand exchange of CdSe has been reacted from an oleic acid ligand to pyridine to increase conductivity. To overcome the general problems of self-aggregation of ligand exchanged inorganic nanoparticles, we carried out a chemical treatment using by a 3-mercaptopropionic acid (3-MPA) on top of ZnO layer for grafting CdSe QDs which give rise to the uniform formation of CdSe QD layer between ZnO and active layer. The CdSe QD interlayer had been confirmed by the confocal microscope image. The ligand exchanged CdSe QD layer contributed to the increased device efficiency over 5% in the inverted organic solar cells due to the role of electron transport and hole blocking effects, which correlated to the enhanced FF from decreased series and increased shunt resistance compared to the device without interlayer.

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