Size-Dependent Energy Transfer Pathways in CdSe Quantum Dot–Squaraine Light-Harvesting Assemblies: Förster versus Dexter

Abstract

Energy transfer coupled with electron transfer is a convenient approach to mimic photosynthesis in light energy conversion. Better understanding of mechanistic details of energy transfer processes is important to enhance the performance of dye or quantum dot-sensitized solar cells. Energy transfer through both long-range dipole-based Förster resonance energy transfer (FRET) and short-range Dexter energy transfer (DET) mechanisms have been identified to occur between CdSe quantum dots (QDs) linked to a red-infrared-absorbing squaraine dye through a short thiol functional group (SQSH). Solutions of SQSH linked to CdSe were investigated through steady-state and time-resolved spectroscopy experiments to explore both mechanisms. Photoluminescence studies revealed that smaller QDs had higher energy transfer efficiencies than predicted by FRET, and femtosecond transient absorption experiments revealed faster energy transfer rates in smaller donor QD sizes. These findings supported a DET process dominating at small donor sizes. The presence of both processes illustrates multiple strategies for utilizing energy transfer in light-harvesting assemblies and the required considerations in device design to maximize energy transfer gains through either mechanism.

Highly Efficient Nonradiative Energy Transfer from Colloidal Semiconductor Quantum Dots to Wells for Sensitive Noncontact Temperature Probing

“…To date, there have been several theoretical and experimental reports on FRET in semiconductor nanocrystals (i.e., colloidal quantum dots (QDs) and nanorods (NRs)) and their hybrids (quantum dot‐conjugated polymer, dye, epitaxial quantum well, etc.) regarding the effects of size, composition, dimensionality and architecture on FRET . Such FRET‐enabled colloidal systems were also shown to be suitable for use in devices including light‐emitting diodes (LEDs) and solar cells …”

Light-driven hydrogen production from aqueous solutions based on a new Dubois-type nickel catalyst

“…Instead, we calculated the ENT rate according to the Förster resonant energy transfer (FRET) model, 44 which has been widely used to estimate the ENT rate in various hybrid systems. [45][46][47][48] According to this model, the estimated ENT time has an upper limit of 5.5 μs, corresponding to an ENT rate of 1.8 × 10 5 s −1 (ESI †). Because the ENT rate is much slower than the 1S electron depopulation rate which is ∼1.8 × 10 10 s −1 (τ ∼ 56 ps) obtained from fitting the kinetic traces in Fig.…”

Impact of FRET between Molecular Aggregates and Quantum Dots

“…The spectroscopic overlap can be tuned by altering the size of the QDs materials. Kamat and co‐workers demonstrated size‐dependent FRET versus Dexter electron‐transfer processes in CdSe QD–squaraine light‐harvesting assemblies . Zaban and co‐workers developed higher‐efficiency built‐in QD antennas in dye‐sensitized solar cells, in which the QD materials served as transmitters to channel the absorbed solar radiation to the dye molecules through a nonradiative energy‐transfer process …”

“…Kamata nd co-workers demonstrated size-dependent FRET versusD exter electron-transfer processes in CdSe QDsquaraine light-harvesting assemblies. [49] Zaban and co-workers developed higher-efficiency built-in QD antennas in dye-sensitized solarc ells, in which the QD materials served as transmitters to channel the absorbed solarr adiation to the dye molecules through anonradiative energy-transfer process. [32] Boron dipyrromethene, commonly known as BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene), consists of ad ifluoroboron moiety in ar igid chelate-like structure.…”