Synchronized Energy and Electron Transfer Processes in Covalently Linked CdSe–Squaraine Dye–TiO₂ Light Harvesting Assembly

Abstract

Manipulation of energy and electron transfer processes in a light harvesting assembly is an important criterion to mimic natural photosynthesis. We have now succeeded in sequentially assembling CdSe quantum dot (QD) and squaraine dye (SQSH) on TiO(2) film and couple energy and electron transfer processes to generate photocurrent in a hybrid solar cell. When attached separately, both CdSe QDs and SQSH inject electrons into TiO(2) under visible-near-IR irradiation. However, CdSe QD if linked to TiO(2) with SQSH linker participates in an energy transfer process. The hybrid solar cells prepared with squaraine dye as a linker between CdSe QD and TiO(2) exhibited power conversion efficiency of 3.65% and good stability during illumination with global AM 1.5 solar condition. Transient absorption spectroscopy measurements provided further insight into the energy transfer between excited CdSe QD and SQSH (rate constant of 6.7 × 10(10) s(-1)) and interfacial electron transfer between excited SQSH and TiO(2) (rate constant of 1.2 × 10(11) s(-1)). The synergy of covalently linked semiconductor quantum dots and near-IR absorbing squaraine dye provides new opportunities to harvest photons from selective regions of the solar spectrum in an efficient manner.

High‐Yield Generation of Triplet Excited States by an Efficient Sequential Photoinduced Process from Energy Transfer to Singlet Fission in Pentacene‐Modified CdSe/ZnS Quantum Dots

“…The other important point includes the far narrower fluorescence spectral regions than those of organic dye molecules. They are thereby one of good candidates for an energy donor because quantum dots are easy to prepare organic–inorganic hybrid materials that utilize the functional groups of an organic dye, such as carboxylic and thiol groups . According to the Förster energy‐transfer theory, the rate constant of the energy‐transfer process is proportional to the spectral overlap between the emission of the donor and absorption of the acceptor and to the inverse sixth power of the distance between the donor and acceptor in a point‐to‐point approximation .…”

“…However, little attention has been given to observe the high‐yield sequential photoinduced process between SF and a different photophysical pathway, such as energy transfer. The molar absorption coefficients of pentacenes in the approximately 400–500 nm region (i.e., blue‐light region) are extremely limited . Consequently, occurrence of efficient energy transfer from an energy donor unit to pentacene (energy acceptor) in this wavelength region is essential for the construction of solar energy conversion systems using SF when considering the entire solar spectrum…”

Assemblies composed of oligothiophene–ruthenium complexes bound to CdSe nanoparticles

“…Although Ru dyes and CdSe nanoparticles have been studied individually and in connection with oligothiophenes [30][31][32][33][34][35], to the best of our knowledge there is no record of studying Ru dyes, oligothiophenes and CdSe in a single system. We have synthesized two new oligothiophenes, trithiophenes 2 and 5 ( Fig.…”

In situ growth of CuInS2 nanocrystals on nanoporous TiO2 film for constructing inorganic/organic heterojunction solar cells

“…This ex situ approach could achieve better control over the sizes and electronic properties of nanocrystals but suffers from low surface coverage and poor electronic coupling [23]. Up to now, many different semiconductor nanocrystals as the sensitizers have been investigated, including CdSe [17,22,25], CdS [21,26], and PbS [27-29]. Unfortunately, these metal chalcogenide semiconductors are easily oxidized when exposed to light, and this unfavorable situation is even more detrimental when the metal sulfide is in contact with a liquid electrolyte containing sulfur.…”