Stabilizing Cu2S for photovoltaics one atomic layer at a time

Area of Science:

• Materials Science
• Solid-State Chemistry
• Photovoltaics

Background:

• Stabilizing stoichiometric copper sulfide (Cu2S), known as chalcocite, is crucial for its application in thin-film photovoltaic (PV) devices.
• Copper deficiency in Cu2S leads to degenerate p-type doping, hindering device performance.
• Controlling copper diffusion into adjacent layers is key to maintaining desirable semiconducting properties.

Purpose of the Study:

• To investigate the stabilization of Cu2S thin films using metal-oxide over- and underlayers.
• To evaluate the impact of different deposition chemistries on film properties.
• To explore the mechanism behind enhanced stabilization.

Main Methods:

• Thin-film deposition of Cu2S with various metal-oxide layers (TiO2, Al2O3).
• Hall measurements and UV-vis-NIR spectroscopy to assess charge carrier concentration and optical properties.
• In situ microbalance and conductivity measurements to study stabilization mechanisms.
• Photoluminescence quenching measurements to evaluate solar energy harvesting potential.

Main Results:

• A 15 nm TiO2 coating significantly suppressed free charge carrier addition in Cu2S films.
• The effectiveness of TiO2 depended strongly on the deposition chemistry.
• An atomic layer of Al2O3 inserted between Cu2S and TiO2 provided remarkable stabilization for over 2 weeks under ambient conditions.
• In situ measurements elucidated the mechanism of stabilization.

Conclusions:

• Metal-oxide layers, especially TiO2 and Al2O3 nanolaminates, can effectively stabilize Cu2S thin films.
• These stabilized films exhibit desirable semiconducting properties for PV applications.
• The findings suggest potential utility of these nanostructured materials in solar energy harvesting.