Silicon nanowire (SiNW) arrays show an excellent light-trapping characteristic and high mobility for carriers. Surface plasmon resonance of silver nanoparticles (AgNPs) can be used to increase light scattering and absorption in solar cells. We fabricated a new kind of SiNW/organic hybrid solar cell by introducing AgNPs. Reflection spectra confirm the improved light scattering of AgNP-decorated SiNW arrays. A double-junction tandem structure was designed to manufacture our hybrid cells. Both short-circuit current and external quantum efficiency measurements show an enhancement in optical absorption of organic layer, especially at lower wavelengths.

The exciton valley dynamics in monolayer WSe ₂ is investigated by the two-color pump–probe magneto-optical Kerr technique.

We study the exciton valley dynamics in monolayers MoSe₂, Mo_0.5W_0.5Se₂, and WSe₂ by employing helicity-resolved two-color transient reflection spectroscopy. The valley depolarization dynamics as a function of the excitation laser energy is studied systematically at above-resonant excitation of excitons at 10 K. A longer intervalley scattering time is obtained as the excitation energy approaches the A exciton resonance for the three studied materials. The excitation energy dependence of exciton valley relaxation proves that the long-range electron-hole exchange interaction dominates the intervalley scattering in transition metal dichalcogenide monolayers. The longer valley scattering time and higher valley polarization degree commonly observed for WSe₂ than for MoSe₂ is discussed to result from the interplay between the intervalley electron-hole exchange interaction and dark-bright exciton scattering, where the existence of energetically lower lying dark excitonic states in monolayer WSe₂ favors the suppression of the intervalley electron-hole exchange interaction.