Abstract
Ultrafast, light-induced dynamics in copper–zinc–tin–sulfide (CZTS) photovoltaic nanoparticles are investigated through a combination of optical and x-ray transient absorption spectroscopy. Laser-pump, x-ray-probe spectroscopy on a colloidal CZTS nanoparticle ink yields element-specificity, which reveals a rapid photo-induced shift of electron density away from Cu-sites, affecting the molecular orbital occupation and structure of CZTS. We observe the formation of a stable charge-separated and thermally excited structure, which persists for nanoseconds and involves an increased charge density at the Zn sites. Combined with density functional theory calculations, the results provide new insight into the structural and electronic dynamics of CZTS absorbers for solar cells.
Highlights
The quaternary compound Cu2ZnSnS4 (CZTS) crystallizing in the kesterite structure1 has been the subject of research as a potential thin-film photovoltaic absorber for more than ten years
We demonstrate that time-resolved x-ray absorption spectroscopy can distinguish the elements participating in the photovoltaic mechanisms in CZTS materials and provide information on how excitation modifies the electronic and nuclear structure
Based on the results and discussion presented above, we suggest the following chronology for the dynamics following 400 nm photoexcitation of CZTS nanoparticles: At the very shortest time scales, 0–0.3 ps, we observe a Cu K-edge difference signal indicating photooxidation from Cu atoms following photoexcitation
Summary
The quaternary compound Cu2ZnSnS4 (CZTS) crystallizing in the kesterite structure has been the subject of research as a potential thin-film photovoltaic absorber for more than ten years. CZTS is a direct bandgap (Eg 1⁄4 1.5 eV) semiconductor, which allows for efficient thin (
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