Among solution-processed nanocrystals containing environmentally benign elements, bismuth sulfide (Bi2S3) is a very promising n-type semiconductor for solar energy conversion. Despite the prompt success in the fabrication of optoelectronic devices deploying Bi2S3 nanocrystals, the limited understanding of electronic properties represents a hurdle for further materials developments. Here, two key materials science issues for light-energy conversion are addressed: bandgap tunability via the quantum size effect, and photocarrier trapping. Nanocrystals are synthesized with controlled sizes varying from 3 to 30 nm. In this size range, bandgap tunability is found to be very small, a few tens of meV. First principles calculations show that a useful blueshift, in the range of hundreds of meV, is achieved in ultra-small nanocrystals, below 1.5 nm in size. Similar conclusions are envisaged for the class of pnictide chalcogenides with a ribbon-like structure [Pn4Ch6]n (Pn = Bi, Sb; Ch = S, Se). Time-resolved differential transmission spectroscopy demonstrates that only photoexcited holes are quickly captured by intragap states. Photoexcitation dynamics are consistent with the scenario emerging in other metal–chalcogenide nanocrystals: traps are created in metal-rich nanocrystal surfaces by incomplete passivation by long fatty acid ligands. In large nanocrystals, a lower bound to surface trap density of one trap every sixteen Bi2S3 units is found.

Colloidal Bi2S3 nanocrystals: Quantum size effects and midgap states

ARESTI, MAURO;SABA, MICHELE;PIRAS, ROBERTO;MARONGIU, DANIELA;MULA, GUIDO;QUOCHI, FRANCESCO;MURA, ANTONIO ANDREA;CANNAS, CARLA;ARDU, ANDREA;ENNAS, GUIDO;MUSINU, ANNA MARIA GIOVANNA;BONGIOVANNI, GIOVANNI LUIGI CARLO
2014

Abstract

Among solution-processed nanocrystals containing environmentally benign elements, bismuth sulfide (Bi2S3) is a very promising n-type semiconductor for solar energy conversion. Despite the prompt success in the fabrication of optoelectronic devices deploying Bi2S3 nanocrystals, the limited understanding of electronic properties represents a hurdle for further materials developments. Here, two key materials science issues for light-energy conversion are addressed: bandgap tunability via the quantum size effect, and photocarrier trapping. Nanocrystals are synthesized with controlled sizes varying from 3 to 30 nm. In this size range, bandgap tunability is found to be very small, a few tens of meV. First principles calculations show that a useful blueshift, in the range of hundreds of meV, is achieved in ultra-small nanocrystals, below 1.5 nm in size. Similar conclusions are envisaged for the class of pnictide chalcogenides with a ribbon-like structure [Pn4Ch6]n (Pn = Bi, Sb; Ch = S, Se). Time-resolved differential transmission spectroscopy demonstrates that only photoexcited holes are quickly captured by intragap states. Photoexcitation dynamics are consistent with the scenario emerging in other metal–chalcogenide nanocrystals: traps are created in metal-rich nanocrystal surfaces by incomplete passivation by long fatty acid ligands. In large nanocrystals, a lower bound to surface trap density of one trap every sixteen Bi2S3 units is found.
File in questo prodotto:
File Dimensione Formato  
AFM Aresti 2014.pdf

Solo gestori archivio

Tipologia: versione editoriale
Dimensione 1.92 MB
Formato Adobe PDF
1.92 MB Adobe PDF   Visualizza/Apri   Richiedi una copia

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11584/110123
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 61
  • ???jsp.display-item.citation.isi??? 59
social impact