New pyrido[3,4-b]pyrazine-based sensitizers for efficient and stable dye-sensitized solar cells

Abstract

A series of new pyrido [3,4-b]pyrazine-based organic sensitizers (PP-I and APP-I-IV) containing different donors and p-spacers have been synthesized and employed in dye-sensitized solar cells (DSSCs). The absorption spectra properties of dyes are analysed by density functional theory (DFT). The calculated results in combination with the experiments suggest that the absorption characteristics and excited state features will mainly be dominated by charge transfer transitions from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) and to higher LUMO orbitals.Furthermore, attaching the octyloxy groups significantly extends the p-conjugation of the donor in APP-IV, which raises the HOMO energy and facilitates its oxidation. As a consequence, APP-IV exhibits the lowest HOMO-LUMO energy gap among all dyes, which, in turn, corresponds well with the red shift of the absorption spectra. Transient photovoltage and photocurrent decay experiments as well as electrochemical impedance spectroscopy indicate that the electron lifetime and charge recombination resistance are increased due to the introduction of octyloxy chains on the donor unit, resulting in the high photovoltage based on APP-IV. It was found that APP-IV based DSSCs with liquid electrolyte display the highest power conversion efficiency (PCE) of 7.12%. Importantly, a PCE of 6.20% has been achieved for APP-IV based DSSCs with ionic-liquid electrolytes and retained 97% of the initial value after continuous light soaking for 1000 h at 60 C. This renders these pyrido [3,4-b]pyrazine-based sensitizers quite promising candidates for highly efficient and stable DSSCs.

New Organic Donor–Acceptor–π–Acceptor Sensitizers for Efficient Dye‐Sensitized Solar Cells and Photocatalytic Hydrogen Evolution under Visible‐Light Irradiation

“…It is necessary to highlight the regiochemistry of 2 b: the pyridal nitrogen atoms of the pyrido [3,4-b]pyrazine unit are orientated towards the triphenylamine donor moiety (proximal configuration). [25] This conformation has been confirmed from the corresponding 1 …”

“…All chemical reactions were carried out under an argon atmosphere. The starting materials 5,8-dibromo-2,3-diphenylquinoxaline [23] and 5,8-dibromo-2,3-diphenylpyrido [3,4-b]pyrazine [25] were synthesized according to published procedures.…”

“…[25] These nanocrystal titania films were treated with a 40 mm aqueous solution of TiCl 4 at room temperature overnight, following by sintering at 450 8C for 30 min. After cooling to room temperature, these films were dipped into a 3 10 À4 m solution of the dyes (AQ, AP) in dichloromethane for 3 h. The electrodes were then rinsed with CH 2 Cl 2 and ethanol and dried.…”

“…[25] This report inspired us to do some further investigation into the application of octyloxydiphenyl-amine as the donor moiety to DSSCs. In this regard, herein, we have designed and synthesized two D-A-p-A-containing organic sensitizers, AQ and AP, by using octyloxydiphenyl-amine as the donor, quinoxaline/pyrido [3,4-b]pyrazine as the auxiliary acceptor, and thiophene as the p bridge (see Scheme 1).…”

“…Similarly, pyrido [3,4-b]pyrazine exhibits a wellknown electron-withdrawing effect due to its two symmetric unsaturated nitrogen atoms and the pyridine nitrogen atoms. [25] They have already been widely utilized and show promising photovoltaic properties in bulk heterojunction solar cells [28][29][30] and DSSCs. [25,[31][32][33] Thus, the quinoxaline and pyrido- [3,4-b]pyrazine unit as a component for constructing novel D-A-p-A sensitizers are a very attractive approach due to their diverse structural modifications and intrinsic strong electronwithdrawing properties.…”