Protective Role of Oxides on Pb-Free Halide Perovskite Surfaces: Interfacial Effects and Excitonic Optical Properties...

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• Lead-free halide perovskites are promising for optoelectronic applications.
• Cesium tin iodide (CsSnI3) perovskites offer a potential lead-free alternative but face stability challenges.
• Germanium dioxide (GeO2) is explored as a protective overlayer to enhance perovskite performance.

Purpose of the Study:

• To investigate the impact of GeO2 overlayers on the stability and optoelectronic properties of Cs(Sn1-xGex)I3 perovskites.
• To understand the interfacial effects between Cs(Sn1-xGex)I3 and GeO2.
• To identify optimal configurations for enhanced photovoltaic performance.

Main Methods:

• First-principles calculations were employed to systematically study the system.
• Slab models of Cs(Sn1-xGex)I3 (x=0.25) with (001) surfaces were constructed.
• Both crystalline and amorphous GeO2 structures were used to model heterointerfaces.

Main Results:

• Ge incorporation reduces exciton binding energy, promoting efficient electron-hole separation.
• Perovskite/GeO2 heterointerfaces show composition- and termination-dependent structural and electronic properties.
• Specific interface configurations were identified that preserve desirable optoelectronic characteristics.
• Amorphous GeO2 models captured the complexity of realistic capping layers.

Conclusions:

• GeO2 overlayers can stabilize (Sn,Ge)-based halide perovskites.
• The electronic properties remain compatible with high-efficiency photovoltaic operation.
• This work provides a microscopic understanding for designing stable and efficient lead-free perovskite solar cells.