Browsing by Author "Wang, Yingying"

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Localized Emitting State and Energy Transfer Properties of Quadrupolar Chromophores and (Multi)Branched Derivatives
(1970-01-01)
Yan, Linyin
;
Chen, Xudong
;
He, Qingguo
;
Wang, Yingying
;
Wang, Xuefei
"In order to better understand the nature of intramolecular charge and energy transfer in multibranched molecules, we have synthesized and studied the photophysical properties of a monomer quadrupolar chromophore with donor-acceptor-donor (D-A-D) electronic push-pull structure, together with its V-shaped dimer and star-shaped trimers. The comparison of steady-state absorption spectra and fluorescence excitation anisotropy spectra of these chromophores show evidence of weak interaction (such as charge and energy transfer) among the branches. Moreover, similar fluorescence and solvation behavior of monomer and branched chromophores (dimer and trimer) implies that the interaction among the branches is not strong enough to make a significant distinction between these molecules, due to the weak interaction and intrinsic structural disorder in branched molecules. Furthermore, the interaction between the branches can be enhanced by inserting pi bridge spacers (-C=C- or -C C-) between the core donor and the acceptor. This improvement leads to a remarkable enhancement of two photon cross sections, indicating that the interbranch interaction results in the amplification of transition dipole moments between ground states and excited states. The interpretations of the observed photophysical properties are further supported by theoretical investigation, which reveal that the changes of the transition dipole moments of the branched quadrupolar chromophores play a critical role in observed the two-photon absorption (2PA) cross-section for an intramolecular charge transfer (ICT) state interaction in the multibranched quadrupolar chromophores."
Solvent-extraction crystal growth for highly efficient carbon-based mesoscopic perovskite solar cells free of hole conductors
(2016)
Chan, Chien-Yi
;
Wang, Yingying
;
Wu, Guan-Wei
;
Diau, Eric Wei-Guang
;
應用化學系
We developed a simple drop-casting method via solvent extraction (SECG) to grow dense and uniform perovskite nanocrystals at room temperature for carbon-based mesoscopic solar cells free of an organic hole-transport layer. The CH3NH3PbI3/N-methyl-2-pyrrolidone (NMP) precursor solution (40%) was first dripped onto a substrate with film configuration TiO2/Al2O3/C and infiltrated at 70 degrees C for 10 min. The perovskite substrate was next immersed in a bath of diethyl ether at 25 degrees C for 30 min. Third, the solventextracted substrate was stored in a dry box (humidity 50%) at 25 degrees C for at least 100 h to complete the crystal growth. The device performance attained a power conversion efficiency (PCE) of 12.3%, which is significantly greater than that of DMF (6.3%) and NMP (8.3%) devices using traditional thermal annealing. The SECG device displayed a superior intrinsic enduring stability: the PCE exceeded 12% for 5000 h with a maximum value of 13.3% without light-soaking at 25 degrees C, but the performance degraded rapidly under one-sun irradiation without encapsulation. To understand the kinetics of charge transfer and defect relaxation for the devices under investigation, we recorded transient photoluminescence decays at an excitation wavelength of 635 nm and a probe wavelength of 770 nm.