Iodine binding with thiophene and furan based dyes for DSCs

Abstract

Iodine binding to thiophene rings in dyes for dye-sensitized solar cells (DSCs) has been hypothesized to be performance degrading in a number of literature cases. Binding of iodine to dyes near the semiconductor surface can promote undesirable electron transfers and lower the overall efficiency of devices. Six thiophene or furan containing dye analogs were synthesized to analyze iodine binding to the dyes via Raman spectroscopy, UV-Vis studies, device performance metrics and density functional theory (DFT) based computations. Evidence suggests I2 binds thiophene-based dyes stronger than furan-based dyes. This leads to higher DSC device currents and voltages from furan analogues, and longer electron lifetimes in DSC devices using furan based dyes. Raman spectrum of the TiO2 surface-bound dyes reveals additional and more instense peaks for thiophene dyes in the presence of I2 relative to no I2. Additionally, broader and shifted UV-Vis peaks are observed for thiophene dyes in the presence of I2 on TiO2 films suggesting significant interaction between the dye molecules and I2. These observations are also supported by DFT and TD-DFT calculations which indicate the absence of a key geometric energy minimum in the dye-I2 ground state for furan dyes which are readily observed for the thiophene based analogues.

A Raman Spectroscopic and Computational Study of New Aromatic Pyrimidine-Based Halogen Bond Acceptors

“…Noteworthy are the applications of halogen bonding interactions in materials research and engineering [22][23][24]. We, like others, have shown the impact of halogen bonding in optoelectronic and semiconducting materials [25][26][27][28][29]. Because of its synthetic accessibility, one of the most common building blocks used in the development of organic semiconducting materials is the sulfur-containing heterocycle thiophene [30].…”

Probing Interfacial Halogen-Bonding Effects with Halogenated Organic Dyes and a Lewis Base-Decorated Transition Metal-Based Redox Shuttle at a Metal Oxide Interface in Dye-Sensitized Solar Cells

“…Halogen bonds typically refer to noncovalent interactions involving a halogen atom, which, to the best of our knowledge, have not yet been probed between transition metal-based RSs and a halogen on an organic dye at a metal oxide surface. The literature has shown significant precedent for the use of a Lewis base or halogen functionality on dyes coordinating to X 2 and X – groups in solution , and at surfaces. − Expanding from X – coordination to transition metal-based RSs with Lewis base functionality coordination could modulate electron-transfer kinetics with these systems. Designing systems with faster electron regeneration kinetics using transition metal-based RSs via self-assembly through noncovalent interactions is therefore an intriguing direction. − This study employs an RS with an accessible peripheral Lewis base site Co­( N -tpy) 2 , where N -tpy is 2,6-di­(pyrid-2-yl)­pyrazine, targeted for studies with a series of organic dyes having a single atom change (Cl, Br, and I) at a TiO 2 semiconductor interface (Figure ).…”

Indolo[3,2-b]indole donor-based D–π–A dyes for DSCs: investigating the role of π-spacers towards recombination

“…The present work is in contrast to the latest report by Delcamp et al on the effect of iodine binding with thiophene and furan p-spacers. 61 They successfully displayed halogen bonding of S to I 2 , employing thiophene as the spacer, which ultimately resulted in lower J sc and V oc values leading to lower photovoltaic performance relative to the furan spacer employing triphenylamine-based D35 analogous dyes. In the present study we show that in addition to the binding of iodine with the heteroatoms, other factors such as the nature of the donor, dihedral angle and aggregation can also contribute to determining the photovoltaic performance when we interchange the spacers.…”