Sang-Wook Lee

We report annealing-free compact TiO_x layer by atomic layer deposition for high efficiency flexible perovskite solar cells, and maintained 95% of the initial PCE after 1000 bending cycles with 10 mm bending radius.

In electrically conductive solids, the Wiedemann-Franz law requires the electronic contribution to thermal conductivity to be proportional to electrical conductivity. Violations of the Wiedemann-Franz law are typically an indication of unconventional quasiparticle dynamics, such as inelastic scattering, or hydrodynamic collective motion of charge carriers, typically pronounced only at cryogenic temperatures. We report an order-of-magnitude breakdown of the Wiedemann-Franz law at high temperature

Black phosphorus attracts enormous attention as a promising layered material for electronic, optoelectronic and thermoelectric applications. Here we report large anisotropy in in-plane thermal conductivity of single-crystal black phosphorus nanoribbons along the zigzag and armchair lattice directions at variable temperatures. Thermal conductivity measurements were carried out under the condition of steady-state longitudinal heat flow using suspended-pad micro-devices. We discovered increasing th

A Nb-doped TiO 2 (NTO) thin film was deposited on a fluorine-doped tin oxide (FTO) electrode by pulsed laser deposition (PLD) and its application as a new compact layer material for dye-sensitized solar cells (DSSCs) was investigated. On the basis of the investigation of the dark current, open circuit voltage ( V oc ) decay, current−voltage ( I − V ) characteristics, and electrochemical impedance spectra (EIS), it was found that the NTO layer functioned as both a blocking layer and an ancillary

The performance of dye-sensitized solar cells (DSSCs) consisting of anatase TiO 2 nanoparticles that were synthesized via a two-step sol−gel process was investigated using electron transport and optical characterizations. Spherical nanoparticles with the average diameter of 20 nm, elongated nanorods with an aspect ratio (AR) of 5, and nanowires with AR = 10 were synthesized. The synthesized nanoparticles possess narrow size distribution, high crystallinity, and negligible surface defects and res

Perovskite solar cells (PSCs) are the most promising candidates as next-generation solar energy conversion systems. To design a highly efficient PSC, understanding electronic properties of mesoporous metal oxides is essential. Herein, we explore the effect of Nb doping of TiO2 on electronic structure and photovoltaic properties of PSCs. Light Nb doping (0.5 and 1.0 at %) increased the optical band gap slightly, but heavy doping (5.0 at %) distinctively decreased it. The relative Fermi level posi

The abrupt first-order metal-insulator phase transition in single-crystal vanadium dioxide nanowires (NWs) is engineered to be a gradual transition by axially grading the doping level of tungsten. We also demonstrate the potential of these NWs for thermal sensing and actuation applications. At room temperature, the graded-doped NWs show metal phase on the tips and insulator phase near the center of the NW, and the metal phase grows progressively toward the center when the temperature rises. As s

We describe the fabrication of crystallographically preferred oriented TiO2 anatase nanotube arrays (p-NTAs) and the characterization of their photovoltaic properties. The preferred orientation to the (004) plane of the TiO2 nanotube array (NTA) was carefully controlled by adjusting the water content in the anodizing electrolyte; ∼2 wt% of water yielded a p-NTA, whereas other contents of water yielded randomly oriented NTAs (r-NTAs). A structural analysis using X-ray diffraction and a high-resol

Vanadium oxides (VxOy) are classic “smart functional materials” used in a wide array of thermochromic, electronic, and catalytic applications. Specifically, vanadium dioxide (VO2) class nanomaterials are of enormous interest due to their unique first order reversible metal-insulator phase transition (MIT) behavior accompanied by a structural phase transition, inducing dramatic changes in electrical and optical properties with large lattice deformation. To date, a plethora of reports exemplifying

This review articles presents a recent progress of continuous process for perovskite module and related issue for the commercialization step of perovskite solar cells.