Giant exciton-enhanced shift currents and direct current conduction with subbandgap photo excitations produced by many-electron interactions

Shift current is a direct current generated from nonlinear light-matter interaction in a noncentrosymmetric crystal and is considered a promising candidate for next-generation photovoltaic devices. The mechanism for shift currents in real materials is, however, still not well understood, especially if electron-hole interactions are included. Here, we employ a first-principles interacting Green's-function approach on the Keldysh contour with real-time propagation to study photocurrents generated by nonlinear optical processes under continuous wave illumination in real materials. We demonstrate a strong direct current shift current at subbandgap excitation frequencies in monolayer GeS due to strongly bound excitons, as well as a giant excitonic enhancement in the shift current coefficients at above bandgap photon frequencies. Our results suggest that atomically thin two-dimensional materials may be promising building blocks for next-generation shift current devices.

Automated summary

Shift current, generated from nonlinear light-matter interaction in noncentrosymmetric crystals, is considered a promising candidate for next-generation photovoltaic devices. The mechanism for shift currents in real materials, especially with electron-hole interactions, is still not well understood. Using first-principles interacting Green's-function approach, this study investigates photocurrents in real materials under continuous wave illumination, showing strong shift currents in monolayer GeS at subbandgap excitation frequencies due to bound excitons, and giant excitonic enhancement in the shift current coefficients at above bandgap photon frequencies. This suggests that atomically thin two-dimensional materials may be promising for next-generation shift current devices.