Molecular Engineering of Pyrido[3,4‐b]pyrazine‐Based Donor–Acceptor–π‐Acceptor Organic Sensitizers: Effect of Auxiliary Acceptor in Cobalt‐ and Iodine‐Based Electrolytes

Abstract

Due to the ease of tuning its redox potential, the cobalt-based redox couple has been extensively applied for highly efficient dye-sensitized solar cells (DSSCs) with extraordinarily high photovoltages. However, a cobalt electrolyte needs particular structural changes in the organic dye components to obtain such high photovoltages. To achieve high device performance, specific requirements in the molecular tailoring of organic sensitizers still need to be met. Besides the need for large electron donors, studies of the auxiliary acceptor segment of donor-acceptor-π-acceptor (D-A-π-A) organic sensitizers are still rare in molecular optimization in the context of cobalt electrolytes. In this work, two novel organic D-A-π-A-type sensitizers (IQ13 and IQ17) have been developed and exploited in cobalt- and iodine-based redox electrolyte DSSCs, specifically to provide insight into the effect of π-bridge modification in different electrolytes. The investigation has been focused on the additional electron-withdrawing acceptor capability with grafted long alkoxy chains. Optoelectronic transient measurements have indicated that IQ17 containing a pyrido[3,4-b]pyrazine moiety bearing long alkoxyphenyl chains is more suitable for application in cobalt-based DSSCs.

Paracelsus‐Preis: M. Grätzel / Werner‐Preis: M. Kovalenko / Ružička‐Preis: H. J. Jessen / Österreichisches Ehrenkreuz für Wissenschaft und Kunst 1. Klasse: B. Kräutler

“…und eine Goldmedaille umfassende Preis geht alle zwei Jahre an einen international anerkannten Wissenschaftler für sein Lebenswerk; Grätzel, der in dieser Rubrik vorgestellt wurde, als ihm der Albert Einstein World Award of Science verliehen worden war, wurde für die Erfindung und Entwicklung der farbstoffsensibilisierten Solarzelle gewürdigt. In Chemistry—A European Journal hat er organische Sensibilisatoren vorgestellt . Grätzel ist einer der Vorsitzenden des Editorial Board von ChemPhysChem und gehört dem Internationalen Beirat der Angewandten Chemie an.…”

Effects of Pyrazine Derivatives and Substituted Positions on the Photoelectric Properties and Electromemory Performance of D–A–D Series Compounds

“…Small organic molecule materials have received considerable attention because of their advantages in determined molecular mass, easy purification, high fluorescent quantum yield, high electroluminescence, and low driving voltage [ 1 , 2 , 3 , 4 ]. Researchers have developed a wide variety of organic optoelectronic materials whose performance can be adjusted through molecular design [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. For example, their solubility can be adjusted by changing the length of the alkyl substituents [ 4 , 5 , 6 ], and their absorption spectrum, carrier mobility, and forbidden band width can be adjusted by changing the type of the substituent [ 7 , 8 , 9 , 10 ] and the link mode [ 11 , 12 , 13 , 14 ].…”

“…Researchers have developed a wide variety of organic optoelectronic materials whose performance can be adjusted through molecular design [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ]. For example, their solubility can be adjusted by changing the length of the alkyl substituents [ 4 , 5 , 6 ], and their absorption spectrum, carrier mobility, and forbidden band width can be adjusted by changing the type of the substituent [ 7 , 8 , 9 , 10 ] and the link mode [ 11 , 12 , 13 , 14 ]. The combination of an electron-rich unit, i.e., an electron donor (D), with electron-donating ability, and an electron-deficient unit, i.e., an electron acceptor (A), with electron-withdrawing ability to construct a D–A–D structure is referred as the D–A strategy [ 11 , 12 , 13 , 14 , 15 , 16 , 17 ].…”

“…Intramolecular charge transfer (ICT) occurs in a D–A molecule, and it affects the molecule’s highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), and band gap, thereby affecting various optoelectronic properties [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. Combining D or A units with similar structures, changing the heteroatoms, or changing the substituents can affect the properties of D–A-type materials [ 7 , 8 , 9 , 10 , 20 , 21 ].…”

“…In addition, pyrazine is very easy to modify, thereby regulating its electron-withdrawing ability. For example, different substituents, such as alkyl chains, benzene rings [ 25 ], and thiophene rings [ 10 , 25 ], can be introduced at the two and three positions of pyrazine, and the pyrazine ring can be fused with an aromatic ring to obtain quinoxaline or pyridopyrazine [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 32 , 33 ]. Pyridine, quinoxaline, and pyridopyrazine contain one N atom, two N atoms, and three N atoms, respectively, and their electron-withdrawing ability gradually increase in this order (e.g., reduction potential versus Hg pool: −0.86 V (pyridopyrazine) > −1.10 V (quinoxaline) > −2.20 V (pyridine)) [ 33 ].…”