In this study, we present a photodetector based on a topological insulator Sb ₂ Te ₃ thin film, which shows an obvious photoresponse to near infrared light with good responsivity, photoconductive gain and detectivity.

The interaction of a single-cycle terahertz electric field with the topological insulator ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ triggers strongly anharmonic lattice dynamics, promoting fully coherent energy transfer between the otherwise noninteracting Raman-active $E_g$ and infrared (IR)-active $E_u$ phononic modes. Two-dimensional terahertz spectroscopy combined with modeling based on the classical equations of motion and symmetry analysis reveals the multistage process underlying the excitation of the Raman-active $E_g$ phonon. In this nonlinear combined photophononic process, the terahertz electric field first prepares a coherent IR-active $E_u$ phononic state and subsequently interacts with this state to efficiently excite the $E_g$ phonon.

Tuning the Fermi level (E_F) in Bi₂Te₃ topological-insulator (TI) films is demonstrated on controlling the temperature of growth with molecular-beam epitaxy (MBE).

Cu/Cu₂O films grown by ion beam sputtering were used as p-type modified layers to improve the efficiency and stability of perovskite solar cells (PSCs) with an n-i-p heterojunction structure. The ratio of Cu to Cu₂O in the films can be tuned by the oxygen flow ratio (O₂/(O₂ + Ar)) during the sputtering of copper. Auger electron spectroscopy was performed to determine the elemental composition and chemical state of Cu in the films. Ultraviolet photoelectron spectroscopy and photoluminescence spectroscopy revealed that the valence band maximum of the p-type Cu/Cu₂O matches well with the perovskite. The Cu/Cu₂O film not only acts as a p-type modified layer but also plays the role of an electron blocking buffer layer. By introducing the p-type Cu/Cu₂O films between the low-mobility hole transport material, spiro-OMeTAD, and the Ag electrode in the PSCs, the device durability and power conversion efficiency (PCE) were effectively improved as compared to the reference devices without the Cu/Cu₂O interlayer. The enhanced PCE is mainly attributed to the high hole mobility of the p-type Cu/Cu₂O film. Additionally, the Cu/Cu₂O film serves as a protective layer against the penetration of humidity and Ag into the perovskite active layer.

We report on helicity-dependent terahertz emissions that originate from the helicity-dependent photocurrents in topological insulator $\mathrm{S}{\mathrm{b}}_2\mathrm{T}{\mathrm{e}}_3$ thin films due to ultrafast optical excitation. The polarity of the emitted terahertz radiation is controlled by both the incident angle and the helicity of optical pulses. Using an unprecedented decomposition-recombination procedure in the time domain, the signals of the Dirac fermions are fully separated from bulk contributions. These results provide insights into the optical coupling of topological surface states and open up opportunities for applying helicity-dependent terahertz emission spectroscopy in spintronics.