Cascading electron and hole transfer dynamics in a CdS/CdTe core–shell sensitized with bromo-pyrogallol red (Br-PGR): slow charge recombination in type II regime

Abstract

Ultrafast cascading hole and electron transfer dynamics have been demonstrated in a CdS/CdTe type II core-shell sensitized with Br-PGR using transient absorption spectroscopy and the charge recombination dynamics have been compared with those of CdS/Br-PGR composite materials. Steady state optical absorption studies suggest that Br-PGR forms strong charge transfer (CT) complexes with both the CdS QD and CdS/CdTe core-shell. Hole transfer from the photo-excited QD and QD core-shell to Br-PGR was confirmed by both steady state and time-resolved emission spectroscopy. Charge separation was also confirmed by detecting electrons in the conduction band of the QD and the cation radical of Br-PGR as measured from femtosecond transient absorption spectroscopy. Charge separation in the CdS/Br-PGR composite materials was found to take place in three different pathways, by transferring the photo-excited hole of CdS to Br-PGR, electron injection from the photo-excited Br-PGR to the CdS QD, and direct electron transfer from the HOMO of Br-PGR to the conduction band of the CdS QD. However, in the CdS/CdTe/Br-PGR system hole transfer from the photo-excited CdS to Br-PGR and electron injection from the photo-excited Br-PGR to CdS take place after cascading through the CdTe shell QD. Charge separation also takes place via direct electron transfer from the Br-PGR HOMO to the conduction band of CdS/CdTe. Charge recombination (CR) dynamics between the electron in the conduction band of the CdS QD and the Br-PGR cation radical were determined by monitoring the bleach recovery kinetics. The CR dynamics were found to be much slower in the CdS/CdTe/Br-PGR system than in the CdS/Br-PGR system. The formation of the strong CT complex and the separation of charges cascading through the CdTe shell help to slow down charge recombination in the type II regime.

Light Harvesting and Photocurrent Generation in a Conjugated Polymer Nanoparticle–Reduced Graphene Oxide Composite

“…[41] In brief, the pump pulse was derived from the frequency doubling of 800 nm laser obtained from Tisapphire laser oscillator (Tissa 50, CDP,M oscow,R ussia) and amplified in am ulti-pass amplifier pumped by a2 0W DPSS laser (Jade-II, Thales Laser,F rance) in a b-barium borate (BBO) crystal at 1kHz repetition rate. The pump power was kept low enough to avoid complications arising from multiexcitons.…”

A visible light induced photoelectrochemical aptsensor constructed by aligned ZnO@CdTe core shell nanocable arrays/carboxylated g-C3N4 for the detection of Proprotein convertase subtilisin/kexin type 6 gene

“…To increase the light-harvesting efficiency, various semiconductor nanocrystals have been adopted to sensitize ZnO, including CdS (Fan et al 2014;Maity et al 2015;Robel et al 2006;, CdSe Jiang and Ju 2007;Jie et al 2011;Josell et al 2014;Robel et al 2006;Zou and Ju 2004), CdTe (Cheng et al 2010;Eley et al 2014;Fan et al 2014;Li et al 2005;, PbS (Eita et al 2015;Karki et al 2014;Zheng et al 2014), PbSe (Chen et al 1998;Oh et al 2014;Schornbaum et al 2014;Zhu et al 2000), InP (Kim et al 2015;Zaban et al 1998) and InAs (Ni et al 2011;Wang et al 2013;Wang et al 2014). Among the most widely used inorganic semiconductor sensitizers, CdTe has a high optical absorption coefficient (10 -4 cm -1 ) and narrow band gap of about 1.5 eV at room temperature and match the preferred range of the radiation spectrum (Cao et al 2007;Shokhovets et al 2007).…”

Tuning Hole and Electron Transfer from Photoexcited CdSe Quantum Dots to Phenol Derivatives: Effect of Electron‐Donating and ‐Withdrawing Moieties

“…Also, in the case of CdSe/CdTet ype II coreshell particles, emission quenching takes place in the presence of 4NP (electron quencher), in which electrons are supposed to localize in the CdSe core (Figure 4f and f'). In our earlier investigation, we have observed that both electron and hole transfer processes from photoexcited QDs to the molecular adsorbatesc an take place on an ultrafast timescale, [24,44,45] which cannot be accounted for by time-resolved emissionq uenching studies. The emission spectrum of the CdSe/ CdTet ype II core-shell particles is broader,r elative to that of CdSe/CdSq uasi-type II core-shell particles, which showse mission maximaa tl = 575 nm with as houlder at l = 555 nm.…”

“…[45] Results and Discussion Characterizationo fC dSe QDs, CdSe/CdTetype II, and CdSe/ CdS quasi-type II NCs Details of the spectrometer are given in the Supporting Information.…”

“…Charge separation has also been demonstrated in type II coreshell nanostructures, in whicho ne of the carrierl eakages to the shell leads to charge separation. [44,45] In QDs, ah igh fraction of atoms reside on the surface ( % 56 %a toms for 3nmQ Ds), which interacts with the surroundings. [42,43] Exciton dissociation in the core-shell structure in the presence of am olecular adsorbate has also been reported by us.…”