Lewis Acid–Lewis Base Interactions Promote Fast Interfacial Electron Transfers with a Pyridine-Based Donor Dye in Dye-Sensitized Solar Cells

Abstract

Increasing the rate of productive interfacial electron transfer reactions in dye-sensitized solar cells is critically important toward improving device performances. Preorganized electron transfer systems at a metal oxide interface are an interesting approach toward favoring fast electron transfer reactions. This study focuses on facilitating electron transfer reactions from a redox shuttle to an oxidized dye at a TiO 2 surface via a transient redox shuttle− dye coordination complex. By design, the cobalt redox shuttle is supported by a pentadentate polypyridyl ligand with a remaining labile coordination site on the metal. The organic dye is designed with pyridyl groups on the donor region for coordinating to the open site on the redox shuttle to preorganize the redox shuttle−dye pair via a Lewis acid−Lewis base interaction. DSC devices fabricated with this dye−redox shuttle pair are studied via current−voltage curves, incident photon-to-current conversion efficiencies (IPCEs), photocurrent dynamics, electrochemical impedance spectroscopy, and transient absorption spectroscopy. Results show that dye binding to the redox shuttle increases the rate of dye regeneration, even in the complex electrolyte environment where coordinating species such as tertbutylpyridine and multiple oxidation states of the redox shuttle are present, leading to a dramatically higher performance of the DSC device under fluorescent lighting (13.0% for [Co(PY5Me 2 )(MeCN)] 3+/2+ versus 5.6% PCE for [Co(bpy) 3 ] 3+/2+ ).

Influence of triphenylamine derivatives in efficient dye-sensitized/organic solar cells

“…Design and synthesis of an organic dye with a D–π–A configuration, DN1 containing pentadentate polypyridyl groups on the dye donor portion as a Lewis base to coordinate with a remaining labile coordination site on the metal in the cobalt redox shuttle to preorganize the redox shuttle–dye pair through a Lewis acid–Lewis base interaction was reported by Jurss et al 86 in 2022. Current–voltage curves, electrochemical impedance spectroscopy, incident photon-to-current conversion efficiencies (IPCEs), photocurrent dynamics, and transient absorption spectroscopy were used to investigate the DSSCs fabricated with this dye-redox shuttle pair.…”

“…In this work, pre-organized electron transfer systems at a metal oxide interface are demonstrated as a promising method to improve device performance by increasing the rate of electron transfer reactions. 86…”

“…In this work, pre-organized electron transfer systems at a metal oxide interface are demonstrated as a promising method to improve device performance by increasing the rate of electron transfer reactions. 86 PCEs of excitonic-type solar cells tend to be severely limited by relatively high voltage loss (V loss ). In 2018, a successful molecular engineering strategy was reported by Zakeeruddin, Grätzel, and co-workers for both the sensitizer and the redox mediator that afforded comprehensive control of the V los s advancing the PCEs of DSSCs.…”

A Theoretical Perspective on the Photochemistry of Boron–Nitrogen Lewis Adducts

“…The versatility of Lewis acid–base adducts, characterized by a dative bond between a Lewis acid and Lewis base, has been extensively used for a plethora of molecular applications like organic synthesis, , catalysis, − and production of new types of dyes for solar cells or polymers. , More recently, a particular boost of interest has emerged for the photochemistry and photophysics of Lewis adducts, with potential applications for functional materials, ,, sensors, , or optoelectronic devices. − For example, the inclusion of a boron atom in polycyclic aromatic hydrocarbons leads to highly stable photoactive molecules, whose optical properties can be altered upon adduct formation with Lewis bases to act as sensors. , These B–N Lewis adducts, however, exhibit a rather peculiar photochemical behavior involving excited-state photodissociation and an unexpected double fluorescence. Interestingly, the light-induced dissociation is not unique to this class of Lewis adducts and has been observed for several compounds containing a constrained boron center paired with a relatively weak Lewis base. ,,− …”

Designing Self-Assembled Dye–Redox Shuttle Systems via Interfacial π-Stacking in Dye-Sensitized Solar Cells for Enhanced Low Light Power Conversion

“…During the regeneration step, the dye and redox shuttle should come into close contact. One approach to improving regeneration is through the noncovalent association of the redox shuttle to the dye via a transient self-assembly process which is known to increase the rate of regenerative electron transfer from the redox shuttle to the oxidized dye. − Self-assembly approaches that have been recently investigated to improve the rate of dye regeneration include halogen bonding, − Lewis acid–Lewis base interactions, and alkyl–alkyl van der Waals interactions . In this context, we envision π-stacking between the redox shuttle and the dye could provide a tunable noncovalent interaction that can be harnessed to promote rapid dye regeneration via association of the redox shuttle to the dye and diffusion of the redox shuttle through the electrolyte after dissociation of the oxidized redox shuttle.…”