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Experimental and first-principles spectroscopy of Cu2SrSnS4 and Cu2BaSnS4 photoabsorbers

DOI: 10.1021/acsami.0c14578 DOI Help

Authors: Andrea Crovetto (Technical University of Denmark; Helmholtz-Zentrum Berlin für Materialien und Energie GmbH) , Zongda Xing (University College London) , Moritz Fischer (Technical University of Denmark) , Rasmus Nielsen (Technical University of Denmark) , Christopher N. Savory (University College London) , Tomas Rindzevicius (Technical University of Denmark) , Nicolas Stenger (Technical University of Denmark) , David O. Scanlon (University College London; Diamond Light Source) , I. B. Chorkendorff (Technical University of Denmark) , Peter C. K. Vesborg (Technical University of Denmark)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acs Applied Materials & Interfaces

State: Published (Approved)
Published: October 2020

Abstract: Cu2BaSnS4 (CBTS) and Cu2SrSnS4 (CSTS) semiconductors have been recently proposed as potential wide band gap photovoltaic absorbers. Although several measurements indicate that they are less affected by band tailing than their parent compound Cu2ZnSnS4, their photovoltaic efficiencies are still low. To identify possible issues, we characterize CBTS and CSTS in parallel by a variety of spectroscopic methods complemented by first-principles calculations. Two main problems are identified in both materials. The first is the existence of deep defect transitions in low-temperature photoluminescence, pointing to a high density of bulk recombination centers. The second is their low electron affinity, which emphasizes the need for an alternative heterojunction partner and electron contact. We also find a tendency for downward band bending at the surface of both materials. In CBTS, this effect is sufficiently large to cause carrier-type inversion, which may enhance carrier separation and mitigate interface recombination. Optical absorption at room temperature is exciton-enhanced in both CBTS and CSTS. Deconvolution of excitonic effects yields band gaps that are about 100 meV higher than previous estimates based on Tauc plots. Although the two investigated materials are remarkably similar in an idealized, defect-free picture, the present work points to CBTS as a more promising absorber than CSTS for tandem photovoltaics.

Journal Keywords: wide band gap absorbers; solar cells; Raman spectroscopy; band gap; excitons; photoluminescence

Diamond Keywords: Photovoltaics; Semiconductors

Subject Areas: Materials, Physics, Energy

Technical Areas:

Added On: 02/11/2020 10:26

Discipline Tags:

Earth Sciences & Environment Climate Change Energy Sustainable Energy Systems Materials Science Energy Materials Physics Surfaces interfaces and thin films

Technical Tags: