Charge Recombination Deceleration by Lateral Transfer of Electrons in Dye-Sensitized NiO Photocathode

Abstract

Control of charge separation and recombination is critical for dye-sensitized solar cells and photoelectrochemical cells, and for p-type cells, the latter process limits their photovoltaic performance. We speculated that the lateral electron hopping between dyes on a p-type semiconductor surface can effectively separate electrons and holes in space and retard recombination. Thus, device designs where lateral electron hopping is promoted can lead to enhanced cell performance. Herein, we present an indirect proof by involving a second dye to monitor the effect of electron hopping after hole injection into the semiconductor. In mesoporous NiO films sensitized with peryleneimide (PMI) or naphthalene diimide (NDI) dyes, dye excitation led to ultrafast hole injection into NiO from either excited PMI* (τ < 200 fs) or NDI* (τ = 1.2 ps). In cosensitized films, surface electron transfer from PMI − to NDI was rapid (τ = 24 ps). Interestingly, the subsequent charge recombination (ps−μs) with NiO holes was much slower when NDI − was generated by electron transfer from PMI − than when NDI was excited directly. We therefore indicate that the charge recombination is slowed down after the charge hopping from the original PMI sites to the NDI sites. The experimental results supported our hypothesis and revealed important information on the charge carrier kinetics for the dye-sensitized NiO photoelectrode system.

A stronger acceptor decreases the rates of charge transfer: ultrafast dynamics and on/off switching of charge separation in organometallic donor–bridge–acceptor systems

“…The X-ray crystal structure of 3 is also given, the alkyl chains have been omitted for clarity. Key bond lengths (Å): Pt1-C1 1.96(2), Pt1-C33 1.98(3), Pt1-P1 2.29 (7), Pt1-P2 2.28 (7), C1-C2 1.25 (3), C33-C34 1.25 (3). Key bond angles: C1-Pt1-P1 91.5 (7), P1-Pt1-C33 88.1 (8), C33-Pt1-P2 86.5 (8), C1-Pt1-P2 93.9 (7).…”

“…Key bond lengths (Å): Pt1-C1 1.96(2), Pt1-C33 1.98(3), Pt1-P1 2.29 (7), Pt1-P2 2.28 (7), C1-C2 1.25 (3), C33-C34 1.25 (3). Key bond angles: C1-Pt1-P1 91.5 (7), P1-Pt1-C33 88.1 (8), C33-Pt1-P2 86.5 (8), C1-Pt1-P2 93.9 (7). CCDC number: 2190247.…”

“…The formation of a charge-separated state (CSS) through photoinduced electron transfer is a key photophysical step in a plethora of light-driven chemical processes, with applications ranging from articial photosynthesis to photocatalysis. [1][2][3][4][5][6][7][8] The modular approaches to control charge separation, whereby, for example, separate molecular units are used for catalysis and light absorption, are accordingly of great interest. Such an approach involves a combination of an electron donor, D, an electron acceptor, A, and a bridge, B 'modules' assembled in a combinatorial fashion.…”

Unveiling photoinduced electron transfer in cobalt(iii)-R-pyridine complexes anchored to anatase nanocrystals: photoluminescence and magnetic studies

“… 24 Furthermore, the subsequent back electron transfer process, involving conduction band electrons and the oxidized form of the sensitizer, occurs at a significantly slower rate than the forward electron transfer reaction. 25 Consequently, this pronounced disparity in rates facilitates effective charge separation, rendering the TiO 2 surface instrumental in achieving long-lived charge separation—a pivotal factor driving investigations in this field. 26 …”