Grain-Resolved Ultrafast Photophysics in Cu2 BaSnS4- x Se x Semiconductors Using Pump-Probe Diffuse Reflectance Spectroscopy and Microscopy.

Journal Article (Journal Article)

In this paper, we analyze fundamental photoexcitation processes and charge carrier kinetics in Cu2 BaSnS4- x Se x (CBTSSe), a recently introduced alternative to Cu(In,Ga)(S,Se)2 and Cu2 ZnSnS4- x Se x (CZTSSe) photovoltaic/photoelectrochemical absorbers, using advanced laser spectroscopy and microscopy techniques. The broadband pump-probe diffuse reflectance spectroscopy technique facilitates monitoring the ultrafast processes in opaque CBTSSe films deposited on Mo-coated glass substrates, similar to the configuration found in functional devices. We spectrally resolve a sharp ground-state bleaching (GSB) peak for CBTSSe films, formed around the band edge transition, which is spectrally narrower than the GSB and stimulated emission in corresponding CZTSSe films. The presence of sharp electronic transitions is further deduced from the ensemble pump-probe spectroscopy and steady-state UV-vis diffuse reflectance spectra. Furthermore, using pump-probe diffuse reflectance scanning microscopy, we monitor the charge carrier formation and excited state pattern within the film grains at few hundred nanometer resolution and localize the kinetics of photogenerated carriers in each grain. The unique sensitivity of pump-probe microscopy and sharp electronic transitions allow for detection of small S/Se stoichiometry variations, Δ x ≤ 0.3, in CBTSSe grains-i.e., features that are largely unresolved for ensemble spectroscopy or luminescence measurements. By noting the sharp band edge transition, we show that the band tailing issue (prevalent for CZTSSe) is largely resolved for CBTSSe; however, other issues may remain, such as deep defects and fast carriers relaxations, which may still impact the photocurrent and open circuit voltage of the CBTSSe devices/films examined.

Full Text

Duke Authors

Cited Authors

  • Ghadiri, E; Shin, D; Shafiee, A; Warren, WS; Mitzi, DB

Published Date

  • November 12, 2018

Published In

Volume / Issue

  • 10 / 46

Start / End Page

  • 39615 - 39623

PubMed ID

  • 30350945

Pubmed Central ID

  • 30350945

Electronic International Standard Serial Number (EISSN)

  • 1944-8252

International Standard Serial Number (ISSN)

  • 1944-8244

Digital Object Identifier (DOI)

  • 10.1021/acsami.8b12307


  • eng