Nanocrystal–Dye Interactions: Studying the Feasibility of Co‐Sensitization of Dyes with Semiconductor Nanocrystals

Abstract

One of the recent developments in enhancing the performance of quantum dot sensitized solar cells (QDSSCs) is to combine QDs with dyes in order to overcome the drawbacks of QDSSCs. However, implementation of this requires a detailed investigation of the interaction between QDs and dye. Here, we have studied the effect of size and surface ligands in the interaction of CdSe nanocrystals (NCs) with Ru N-719 dye. The interaction mechanism is investigated by steady-state and time-resolved photoluminescence spectroscopy, indicating the involvement of apparent static as well as dynamic quenching. Further analysis of dynamic quenching reveals the contribution of Förster resonance energy transfer and electron transfer from NCs to the dye. The Marcus model of electron transfer rationalizes the random trends of experimental electron transfer rates, which depend on the energetic offsets between the two species and the reorganizational energy. For understanding the kinetics of energy/charge transfer from CdSe NCs to Ru N-719 dye, a Poisson binding model has been proposed that assumes a Poisson distribution of dye molecules around CdSe NCs. The variation of quenching rate constants and PL quenching rate both follow the same trend, supporting the main contribution of kinetics in the interaction of CdSe NCs with the dye.

High‐Efficiency FRET Processes in BODIPY‐Functionalized Quantum Dot Architectures

“…However, due to the large surface area of the QDs, the interaction of more than one dye molecule on the same QD donor can be expected [4, 10a, 11, 25] …”

“…A more precise calculation can be obtained by a method based on the Poisson distribution of the dye molecules around the QDs. Such a method, [4, 10a, 25g, 26] allows to determine the average number of acceptors for each QD, based on the fitting of the time resolved decay of the FRET systems with a function that takes into account the Poisson distribution. The calculations, reported in the Supporting Information, indicate an average number of about 1.5 molecules of MASB and 1.1 of DASB, respectively, per QD.…”

“…In Equation 4, F D (l)i st he donor fluorescence intensity, while e A (l)i st he acceptor molar absorption coefficient, both dependento nl. In order to obtain R 0 values in units of nm, the spectral overlapi ntegral J(l)h as been calculated in m À1 cm À1 nm 4 ,b yu sing nm and m À1 cm À1 as units for l and e A (l), respectively,inE quation (4). Figure 4s hows the overlap integrals J(l)b etween the PL of the QD donor and the extinction spectrao ft he dyea cceptor and highlightst he presence of as trongr esonance for MASB (A), significantly weaker forD ASB (B).…”

“…The FRET process is an excitation energy transfer occurring via a non‐radiative dipole‐dipole interaction between an excited donor (D) and an acceptor (A). The FRET efficiency depends on the spectral overlap between the donor fluorescence and the acceptor extinction, on the D–A separation distance, typically ranging from few Å to 10 nm, and on the relative orientation between the transition dipole moments of donor and acceptor [4] . Moreover, according to the classical FRET theory, a high quantum yield (QY) of the donor is required to maximize the process efficiency [5] …”

“…The FRET efficiency dependso n the spectralo verlap betweenthe donor fluorescence and the acceptore xtinction, on the D-A separation distance, typically ranging from few to 10 nm, and on the relative orientation betweent he transition dipole moments of donor anda cceptor. [4] Moreover,a ccording to the classical FRET theory,ahigh quantum yield (QY) of the donor is requiredt om aximize the process efficiency. [5] Inorganic quantum dots (QDs) are being increasingly exploited as donors in FRET systems, thanks to their broad absorption spectra,t he size-tunable narrow emission, the high QY and the excellent chemical and photostability.B esides,Q Ds offer the benefito fm inimizingt he acceptor direct excitation, as their broad absorption band allows excitation in al arge portiono f the UV/Vis spectrum,a nd to tune the FRET efficiency by hosting multiple acceptors per QD.…”