The research deals with fabrication of CdS/CdSe-sensitized quantum dot sensitized solar cells (QDSSCs) with laser-engineered black rutile TiO 2 nanoparticles (TiO 2 -NPs) as the photoanode material. Three QDSSC devices with pristine and two types of black rutile TiO 2 -NPs engineered respectively in water and ethanol by intense femtosecond laser propagating in the filamentation regime were prepared in the same architecture. Extremely different power conversion efficiencies (PCE) of 1.43 %, 3.68 % and 9.11 %, in which the black TiO 2 -NPs-based devices show respectively a two-fold and six-fold PCE higher than the pristine TiO 2 -NPs, were obtained. The absorption and electrochemical impedance spectroscopy analyses revealed that the device with the highest PCE has the highest absorption efficiency in the wide spectral range from UV to mid-infrared and shunt resistance ( R sh ) of 1364.9 Ω, but the smallest series resistance ( R s ) of 190.3 Ω, which are attributed to the surface modification on the structural and optical properties of TiO 2 -NPs by femtosecond laser pulses.
Light engineering of correlated states in topological materials provides a new avenue of achieving exotic topological phases inaccessible by conventional tuning methods. Here we demonstrate a light control of correlation gaps in a model charge-density-wave (CDW) and polaron insulator (TaSe 4 ) 2 I recently predicted to be an axion insulator. Our ultrafast terahertz photocurrent spectroscopy reveals a two-step, non-thermal melting of polarons and electronic CDW gap via the fluence dependence of a longitudinal circular photogalvanic current. This helicity-dependent photocurrent reveals continuous ultrafast phase switches from the polaronic state to the CDW (axion) phase, and finally to a hidden Weyl phase as the pump fluence increases. Additional distinctive attributes aligning with the light-induced switches include: the mode-selective coupling of coherent phonons to the polaron and CDW modulation, and the emergence of a non-thermal chiral photocurrent above the pump threshold of CDW-related phonons. The demonstrated ultrafast chirality control of correlated topological states here holds large potentials for realizing axion electrodynamics and advancing quantum-computing applications.
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