Chemically tuned intermediate band states in atomically thin CuxGeSe/SnS quantum material for photovoltaic applications.

A new generation of quantum material derived from intercalating zerovalent atoms such as Cu into the intrinsic van der Waals gap at the interface of atomically thin two-dimensional GeSe/SnS heterostructure is designed, and their optoelectronic features are explored for next-generation photovoltaic applications. Advanced ab initio modeling reveals that many-body effects induce intermediate band (IB) states, with subband gaps (~0.78 and 1.26 electron volts) ideal for next-generation solar devices, which promise efficiency greater than the Shockley-Queisser limit of ~32%. The charge carriers across the heterojunction are both energetically and spontaneously spatially confined, reducing nonradiative recombination and boosting quantum efficiency. Using this IB material in a solar cell prototype enhances absorption and carrier generation in the near-infrared to visible light range. Tuning the active layer's thickness increases optical activity at wavelengths greater than 600 nm, achieving ~190% external quantum efficiency over a broad solar wavelength range, underscoring its potential in advanced photovoltaic technology.

Tailoring Ultrafast Near-Band Gap Photoconductive Response in GeS by Zero-Valent Cu Intercalation.

Zero-valent intercalation of atomic metals into the van der Waals gap of layered materials can be used to tune their electronic, optical, thermal, and mechanical properties. Here, we report the impact of intercalating ∼3 atm percent of zero-valent copper into germanium sulfide (GeS). Advanced many-body calculations predict that copper introduces quasi-localized intermediate band states, and time-resolved THz spectroscopy studies demonstrate that those states have prominent effects on the photoconductivity of GeS. Cu-intercalated GeS exhibits a faster rise of transient photoconductivity and a shorter lifetime of optically injected carriers following near-gap excitation with 800 nm pulses. At the same time, Cu intercalation improves free carrier mobility from 1100 to 1300 cm2 V-1 s-1, which we attribute to the damping of acoustic phonons observed in Brillouin scattering and consequent reduction of phonon scattering.