Facile in situ Synthesis of Ag‐Doped CdSe Supra‐Quantum Dots and their Characterization

Abstract

A supra‐quantum dot (SQD) is a three‐dimensionally assembled QD structure composed of several hundreds to thousands of QDs connected through oriented attachments. Owing to their three‐dimensional interconnected structures and relatively large volumes, impurity atoms are thermodynamically more stable in SQDs than in conventional QDs. Herein, we report the facile in‐situ synthesis of colloidal Ag‐doped CdSe SQDs. Ag dopants were efficiently incorporated into CdSe SQDs through the three‐dimensional interconnection of Ag‐doped primary CdSe QDs, as confirmed by elemental analysis combined with chemical etching. Photoelectron spectroscopic studies revealed that the Ag‐doped CdSe SQDs exhibit n‐type doping behavior, since the valence electrons from the interstitial Ag atoms are directly donated to the lattice.

Size-Dependent Photovoltaic Performance of CdSe Supraquantum Dot/Polymer Hybrid Solar Cells: “Goldilocks Problem” Resolved by Tuning the Band Alignment Using Surface Ligands

“…The 4.3 nm-sized CdSe QD sample exhibited resolved transition features in the absorption spectrum, with the first excitonic peak at 581 nm, while the peak shifted to 614 nm for the 17 nm-sized branched NC sample. For the CdSe SQD samples, the band-edge absorption peaks shifted to red, and the peak shapes appeared broad and featureless because of the weakly confined exciton characteristics associated with the interconnected internal SQD structures. , The 46 nm-sized SQD sample showed a band-edge peak at 622 nm, while the band-edge peaks for the 55, 64, and 94 nm-sized SQD samples were observed at approximately 635 nm; the band-edge peak positions of the SQD samples were determined using the first minimum from the second derivative of the absorption spectra …”

“…For the CdSe SQD samples, the band-edge absorption peaks shifted to red, and the peak shapes appeared broad and featureless because of the weakly confined exciton characteristics associated with the interconnected internal SQD structures. 30,36 The 46 nm-sized SQD sample showed a band-edge peak at 622 nm, while the band-edge peaks for the 55, 64, and 94 nm-sized SQD samples were observed at approximately 635 nm; the band-edge peak positions of the SQD samples were determined using the first minimum from the second derivative of the absorption spectra. 38 The CdSe NCs including QDs, branched NCs, and SQDs/ P3HT BHJ solar cells were fabricated with the device structure of ITO/PEDOT:PSS/CdSe NCs:P3HT/Al.…”

“…We previously reported on the three-dimensional (3-D), nearly monodispersed colloidal II–VI superstructures that consist of several hundreds to thousands of QDs connected by dipole-induced oriented attachment, namely, supraquantum dots (SQDs) . Furthermore, various kinds of assembled semiconductor QD-based superstructures have been reported previously; however, using them in photovoltaic devices was unsuitable as photogenerated charge transport within the assembled superstructures could be impeded by the individual QD surface ligands. − However, strong electronically coupled QDs without insulating organic ligands, such as QD solid particles, permit facile charge transport within the internal SQD. , In this study, we investigated the effect of the size of the CdSe NC on CdSe/P3HT hybrid BHJ devices utilizing the tens of nanometers of the SQD structure. The PCEs of the devices enhanced as the size of the CdSe NC increased by reducing the interparticle hopping events for extracting electrons toward the cathode.…”

“…31−33 However, strong electronically coupled QDs without insulating organic ligands, such as QD solid particles, 34 permit facile charge transport within the internal SQD. 35,36 In this study, we investigated the effect of the size of the CdSe NC on CdSe/P3HT hybrid BHJ devices utilizing the tens of nanometers of the SQD structure. The PCEs of the devices enhanced as the size of the CdSe NC increased by reducing the interparticle hopping events for extracting electrons toward the cathode.…”