박지상 교수

The behavior of grain boundaries in polycrystalline halide perovskite solar cells remains poorly understood. Whereas theoretical studies indicate that grain boundaries are not active for electron–hole recombination, there have been observations of higher nonradiative recombination rates involving these extended defects. We find that iodine interstitial defects, which have been established as a recombination center in bulk crystals, tend to segregate at planar defects in CsPbI3. First-principles

The electronic structure and related optical properties of an emerging thin-film photovoltaic material CH3NH3PbBr3 are studied. A block-shaped α-phase CH3NH3PbBr3 single crystal with the natural ⟨100⟩ surface is synthesized solvothermally. The room-temperature dielectric function ε = ε1 + iε2 spectrum of CH3NH3PbBr3 is determined by spectroscopic ellipsometry from 0.73 to 6.45 eV. Data are modeled with a series of Tauc-Lorentz oscillators, which show the absorption edge with a strong excitonic t

Abstract Hierarchically ordered structures facilitate the incorporation of diverse functions simultaneously. The present report introduces a simple and novel strategy for producing hierarchically ordered polymeric films. Hierarchical ordering of aqueous droplets on a polymer solution is realized by the imposition of physical confinement via various shaped gratings. After drying of the solution, well‐ordered hierarchical structures were fabricated in the remaining polymer film. The size of the gr

The origin of the ballistic hole gas recently observed in Ge/Si core-shell nanowires has not been clearly resolved yet, although it is thought to be the result of the band offset at the radial interface. Here we perform spin-polarized density-functional calculations to investigate the defect levels of surface dangling bonds and Au impurities in the Si shell. Without any doping strategy, we find that Si dangling bond and substitutional Au defects behave as charge traps, generating hole carriers i

The behaviour of grain boundaries in polycrystalline halide perovskite solar cells remains poorly understood. Whereas theoretical studies indicate that grain boundaries are not active for electron-hole recombination, there have been observations of higher non-radiative recombination rates involving these extended defects. We find that iodine interstitial defects, which have been established as a recombination center in bulk crystals, tend to segregate at planar defects in CsPbI3. First-principle

Low-defect-density Ge epitaxy was fabricated using aspect ratio trapping combined with epitaxial lateral overgrowth techniques. Dislocations from the interface were trapped inside oxide trenches, and then Ge was laterally grown to form wide, long strips. Chemical mechanical polishing of Ge was used to planarize the faceted strips. Uncoalesced Ge strips showed a defect density as low as from plan-view transmission electron microscopy, while coalesced Ge had higher defect density. This approach sh

Chiral perovskites have emerged as promising candidates for polarization-sensing materials. Despite their excellent chiroptical properties, the nature of their multiple-quantum-well structures is a critical hurdle for polarization-based and spintronic applications. Furthermore, as the origin of chiroptical activity in chiral perovskites is still illusive, the strategy for simultaneously enhancing the chiroptical activity and charge transport has not yet been reported. Here, we demonstrated that

Abstract The rapid advancement of AI‐enabled applications has resulted in an increasing need for energy‐efficient computing hardware. Logic‐in‐memory is a promising approach for processing the data stored in memory, wherein fast and efficient computations are possible owing to the parallel execution of reconfigurable logic operations. In this study, a dual‐logic‐in‐memory device, which can simultaneously perform two logic operations in four states, is demonstrated using van der Waals ferroelectr

Using first-principles density functional calculations, we investigate the relative stability and electronic structure of the grain boundaries (GBs) in zinc-blende CdTe. Among the low-Σ-value symmetric tilt Σ3 (111), Σ3 (112), Σ5 (120), and Σ5 (130) GBs, we show that the Σ3 (111)GB is always the most stable due to the absence of dangling bonds and wrong bonds. The Σ5 (120) GBs, however, are shown to be more stable than the Σ3 (112) GBs, even though the former has a higher Σ value, and the latter

Structural deformation modifies the bandgap, exciton fine structure and phonon energy of semiconductors, providing an additional knob to control their optical properties. The impact can be exploited in colloidal semiconductor quantum dots (QDs), wherein structural stresses can be imposed in three dimensions while defect formation is suppressed by controlling surface growth kinetics. Yet, the control over the structural deformation of QDs free from optically active defects has not been reached. H

Solar cells are semiconductor devices that generate electricity through charge generation upon illumination. For optimal device efficiency, the photogenerated carriers must reach the electrical contact layers before they recombine. A deep understanding of the recombination process and transport behavior is essential to design better devices. Halide perovskite solar cells are commonly made of a polycrystalline absorber layer, but there is no consensus on the nature and role of grain boundaries. T

InAs semiconductor nanocrystals (NCs) exhibit intriguing electrical/optoelectronic properties suitable for next-generation electronic devices. Although there is a need for both n - and p -type semiconductors in such devices, InAs NCs typically exhibit only n -type characteristics. Here, we report InAs NCs with controlled semiconductor polarity. Both p - and n -type InAs NCs can be achieved from the same indium chloride and aminoarsine precursors but by using two different reducing agents, diethy

Bi or Sb doping has been used to make better material properties of polycrystalline Cu2(In,Ga)Se2 as solar cell absorbers, including the experimentally observed improved electrical properties. However, the mechanism is still not clear. Using first-principles method, we investigate the stability and electronic structure of Bi- and Sb-related defects in CuInSe2 and study their effects on the doping efficiency. Contrary to previous thinking that Bi or Sb substituted on the anion site, we find that

Excess charge carriers in metal halide perovskite layer have been known to accelerate degradation of the film and devices to cause poor operational stability of perovskite solar cells (PSCs). While mechanisms for such degradation have been predominantly studied for methylammonium‐based perovskites, effects of excess charge carriers and their interplays with other degradation causes are barely studied for widely used formamidinium‐based perovskites. Herein, a possible decomposition mechanism of t