Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells with low cost and eco-friendly characteristics are attractive as future sources of electricity generation, but low conversion efficiency remains an issue. To improve conversion efficiency, a method of inserting intermediate layers between the CZTSSe absorber film and the Mo back contact is used to suppress the formation of MoSe₂ and decomposition of CZTSSe. Among the candidates for the intermediate layer, graphene oxide (GO) and reduced GO have excellent properties, including high-charge mobility and low processing cost. Depending on the type of GO, the solar cell parameters, such as fill factor (FF), were enhanced. Thus, the conversion efficiency of 6.3% was achieved using the chemically reduced GO intermediate layer with significantly improved FF.

We have estimated the intrinsic complex refractive index spectrum of a CsPbBr₃ nanocrystal. With various dilute solutions of CsPbBr₃ nanocrystals dissolved in toluene, effective refractive indices were measured at two different wavelengths using Michelson interferometry. Given the effective absorption spectrum of the solution, a full spectrum of the effective refractive index was also obtained through the Kramers–Krönig relations. Based on the Maxwell–Garnett model in the effective medium approximation, the real and imaginary spectrum of the complex refractive index was estimated for the CsPbBr₃ nanocrystal, and the dominant inaccuracy was attributed to the size inhomogeneity.

We report on new THz electromagnetic emission mechanism from deformational coupling of acoustic (AC) phonons with electrons in the propagation medium of non-polar Si. The epicenters of the AC phonon pulses are the surface and interface of a GaP transducer layer whose thickness (d) is varied in nanoscale from 16 to 45 nm. The propagating AC pulses locally modulate the bandgap, which in turn generates a train of electric field pulses, inducing an abrupt drift motion at the depletion edge of Si. The fairly time-delayed THz bursts, centered at different times ( t 1 T H z , t 2 T H z , and t 3 T H z ), are concurrently emitted only when a series of AC pulses reach the point of the depletion edge of Si, even without any piezoelectricity. The analysis on the observed peak emission amplitudes is consistent with calculations based on the combined effects of mobile charge carrier density and AC-phonon–induced local deformation, which recapitulates the role of deformational potential coupling in THz wave emission in a formulatively distinct manner from piezoelectric counterpart.

We demonstrate that the thermal boundary conductivity (TBC) between graphene and GaN-based light-emitting diodes (LEDs) can be manipulated through thermal annealing, which is verified by measuring the acoustic phonons after reflection at the interface. Thermal annealing affects the interfacial morphology as evaluated by both the Raman spectra and the spatial profile of the graphene wrinkles in atomic force microscopy. By tracing the phase of ultrafast acoustic oscillations on the basis of the pump-probe scheme, we extract the phonon reflection coefficient at the interface as a function of annealing temperatures up to 400 ${}^{°}$ C. Specifically, the phase shift of transient phononic oscillations at the graphene/LED interface conveys the photoelastic response during the phonon transfer process and can be used for extracting the interfacial coupling rate, which is strongly enhanced around $\approx 200{}^{°}$ C. By incorporating the heat capacity and the interfacial coupling constants into TBC, along with analytical modeling based on the phonon reflection coefficients, we show that the TBC increases with the minimized surface roughness of graphene side at 200 ${}^{°}$ C. This new comprehensive TBC extraction scheme could spark further discussion on improving the heat dissipation of LEDs.

We present an effective protocol for extracting localization energy from WSe₂ monolayers, based on temperature-dependent spectral variation of photoluminescence (PL), and observe time-sequential changes over a long period of time. We found that even freshly exfoliated WSe₂ exhibits deviation from the Varshni formula upon exposure to air, while the temperature-dependent PL lineshapes of h-BN encapsulated WSe₂ match well with delocalized features for as long as two years of the aging period. Our findings support the prospect of h-BN encapsulation for monoatomic transition metal dichalcogenides to meet the longevity condition, which is a prerequisite for practical components in the electronics industry.