Haiya Sun

Enhanced Internal Quantum Efficiency in Dye-Sensitized Solar Cells: Effect of Long-Lived Charge-Separated State of Sensitizers

Effective charge separation is one of the key determinants for the photovoltaic performance of the dye-sensitized solar cells (DSSCs). Herein, two charge-separated (CS) sensitizers, MTPA-Pyc and YD-Pyc, have been synthesized and applied in DSSCs to investigate the effect of the CS states of the sensitizers on the devices efficiency. The CS states with lifetimes of 64 and 177 ns for MTPA-Pyc and YD-Pyc, respectively, are formed via the photoinduced electron transfer (PET) from the 4-styryltriphenylamine (MTPA) or 4-styrylindoline (YD) donor to the pyrimidine cyanoacrylic acid (Pyc) acceptor. DSSCs based on MTPA-Pyc and YD-Pyc exhibit high internal quantum efficiency (IQE) values of over 80% from 400 to 600 nm. In comparison, the IQEs of the charge transfer (CT) sensitizer cells are 10-30% lower in the same wavelength range. The enhanced IQE values in the devices based on the CS sensitizers are ascribed to the higher electron injection efficiencies and slower charge recombination. The results demonstrate that taking advantage of the CS states in the sensitizers can be a promising strategy to improve the IQEs and further enhance the overall efficiencies of the DSSCs.

Tuning photophysical properties via alkoxyl groups in charge-separated triphenylamine sensitizers for dye-sensitized solar cells

Abstract Two charge-separated (CS) sensitizers ( MoTPA-Pyc and OcTPA-Pyc ) with methoxyl or octyloxyl groups attached to the para position of the triphenylamine donor moiety were synthesized to investigate the effect of the alkoxyl groups on the photophysical properties of the CS sensitizers and photovoltaic performances of the corresponding dye-sensitized solar cells (DSSCs). The introduction of alkoxyl groups can increase the energy gap between LUMO+1 and LUMO, leading to an increased intramolecular photo-induced electron transfer (PET) efficiency. Both MoTPA-Pyc and OcTPA-Pyc show elongated lifetimes for their CS states, resulting in an enhanced internal quantum efficiency (IQE) of DSSCs. It has been demonstrated that intramolecular PET is the key step for efficient DSSCs due to the presence of long-lived CS states allowing efficient and fast interfacial electron transfer from the CS sensitizers to the TiO 2 nanoparticles. The best efficiency of 5.76% was achieved by the MoTPA-Pyc based DSSC through a combined contribution of high IQE and efficient light harvesting. The results suggest that enhancing the intramolecular PET efficiency and the light harvesting ability of the dye-loaded TiO 2 film are effective strategies for achieving higher photovoltaic performance for CS sensitizer-based DSSCs.

Facile Synthesis of [1,2,4]Triazolo[4,3-a]pyrazin-3-amines via Oxidative Cyclization of 1-(Pyrazin-2-yl)guanidine Derivatives

In this study, we applied a novel, mild, and convenient synthetic method involving the oxidative cyclization of 1-(pyrazin-2-yl)guanidine derivatives to produce [1,2,4]triazolo[4,3-a]pyrazin-3-amines. We optimized the reaction procedure to easily obtain 5-chloro-[1,2,4]triazolo[4,3-a]pyrazin-3-amine. Various types of halogenated pyrazines can successfully undergo this process. We synthesized a series of 1-(pyrazin-2-yl)guanidines and [1,2,4]triazolo[4,3-a]pyrazin-3-amines, and then elucidated their structures based on their 1H-NMR, 13C-NMR, ESI-HRMS, and nuclear Overhauser effect spectra.