Enhancing photoluminescence quenching and photoelectric properties of CdSe quantum dots with hole accepting ligands

Abstract

CdSe quantum dots have been encapped with aromatic ligands: a-toluenethiol, thiophenol, and p-hydroxythiophenol to enhance the photoluminescence (PL) quenching and photoelectric properties of the quantum dots. The aromatic ligand capped CdSe quantum dots are prepared through ligand exchange with trioctylphosphine oxide (TOPO) capped CdSe quantum dots. The XPS surface chemistry analysis and elemental analysis has confirmed the success of ligand exchange from TOPO to aromatic ligands. Both XRD and HRTEM-SAED studies indicate the crystalline structure of CdSe quantum dots not only remains but is also improved by the ligand exchange of TOPO with thiol molecules. Time resolved PL decay measurements indicate thiophenol and p-hydroxythiophenol ligands effectively quench the emission and have much shorter PL lifetimes than that of TOPO and that of a-toluenethiol. Thus, both thiophenol and p-hydroxythiophenol can act as an effective acceptor for photogenerated holes through aromatic p-electrons. Thiophenol also exhibits good charge transport behavior showing a 10-fold increase in short circuit current density (I sc ) as compared with TOPO in the photocurrent study of fabricated photovoltaic devices.

The Effect of Quantum Dot Shell Structure on Fluorescence Quenching By Acridine Ligand

“…The absorption bands of AL in the wavelength region between 300 and 450 nm are considered as the π-π transitions of the complex π -conjugated system of acridine [20]. Photoluminescence and absorption maxima of AL in aqueous solution ( Fig.…”

“…HOMO and LUMO energy levels [16,17] of 4,5-acridine derivatives are comparable to the ones of semiconductor nanocrystals [18], what allows to use acridine-based molecules as hole transporting material in designing of perovskite solar cells [16] and light-emitting diodes [19]. On the other hand, such a charge transfer leads to the problem of QD fluorescence quenching [20,21] by photoinduced electron transfer (PET) [22]. This hampers the use of acridine derivatives as targeting agents in designing QD-based nanoprobes.…”

Transient absorption studies of CdSe nanocluster passivated with phenyldithiocarbamate ligands.

“…[47] Over the past decade, organic ligands that either withdraw electrons from or donate electrons (i.e., withdraw holes) to the QD cores, have drawn great attentions to researchers [31,[48][49][50][51][52]. Ligands with aromatic rings are especially interesting due to their piconjugation structure which offers the strong ability to extract photon-generated charge carriers from the QDs surface [49,[53][54][55].…”

“…This electron withdrawing or donating effect is attributed to the conjugation structures, the aromaticity, and the functional groups of the ligand molecules [269,270]. Ligands with aromatic rings (such as thiophenol [53], aniline [54], phenylenediamine [49,55]) are especially interesting due to their pi-conjugation structures which offer the strong ability to extract photongenerated charge carriers from the QDs core to the passivated ligands.…”

“…This effect is especially important for semiconductor nanoclusters with a diameter that is less than 2 nm, and hence 80% or more atoms are on the surface [230]. Researchers have been using inorganic shells such as ZnS, CdS and CdTe [64,263,264] or organic ligands [53,265,266] to passivate the surface atoms. Surface passivation can modulate the optical properties of the QDs and prevent charge trapping states due to defects, which sabotage the efficiencies of photovoltaic devices [267,268].…”