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Direct, Indirect, and Self-Trapped Excitons in Cs2AgBiBr6.
Mehmet Baskurt1, Paul Erhart1, Julia Wiktor1
1Department of Physics, Chalmers University of Technology, 41296 Gothenburg, Sweden.
This study reveals that Cs2AgBiBr6 has competing excited states, explaining its light-emitting properties. Advanced computational methods accurately predict its absorption spectrum and band gap, crucial for solar cell and LED applications.
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Area of Science:
- Materials Science
- Solid-State Physics
- Computational Chemistry
Background:
- Cesium silver bismuth bromide (Cs2AgBiBr6) is a halide double perovskite with potential for solar cells and LEDs.
- Understanding its excited states is key to optimizing its optoelectronic properties.
Purpose of the Study:
- Investigate the excited states of Cs2AgBiBr6.
- Accurately predict its absorption and emission properties.
- Clarify the origins of its photoluminescence.
Main Methods:
- Time-dependent density functional theory (TD-DFT).
- Nonempirical hybrid functionals: PBE0(α) and dielectric-dependent hybrids (DDH).
- Analysis of direct, indirect, and self-trapped excitons.
Main Results:
- TD-DFT with hybrid functionals accurately predicts the absorption spectrum.
- The fundamental band gap of Cs2AgBiBr6 was underestimated in prior studies.
- Experimental photoluminescence at 1.9-2.0 eV is linked to self-trapped excitons and electron polarons.
- A complex interplay of direct, indirect, and self-trapped excitons was identified.
Conclusions:
- Advanced computational methods provide accurate predictions for Cs2AgBiBr6 optoelectronic properties.
- Self-trapped excitons and electron polarons are responsible for the observed photoluminescence.
- The findings offer insights into halide double perovskites for next-generation optoelectronic devices.