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Ge 4s2 lone pairs and band alignments in GeS and GeSe for photovoltaics

DOI: 10.1039/D1TA05955F DOI Help

Authors: Matthew J. Smiles (University of Liverpool) , Jonathan M. Skelton (University of Manchester) , Huw Shiel (University of Liverpool) , Leanne A. H. Jones (University of Liverpool) , Jack E. N. Swallow (University of Liverpool) , Holly J. Edwards (University of Liverpool) , Thomas Featherstone (University of Liverpool) , Philip A. E. Murgatroyd (University of Liverpool) , Pardeep K. Thakur (Diamond Light Source) , Tien-Lin Lee (Diamond Light Source) , Vinod R. Dhanak (University of Liverpool) , Tim D. Veal (University of Liverpool)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Materials Chemistry A

State: Published (Approved)
Published: September 2021
Diamond Proposal Number(s): 21431 , 23160

Open Access Open Access

Abstract: Germanium sulfide and germanium selenide bulk crystals were prepared using a melt growth technique. X-ray photoemission spectroscopy (XPS) was used to determine ionisation potentials of 5.74 and 5.48 eV for GeS and GeSe respectively. These values were used with the previously-measured band gaps to establish the natural band alignments with potential window layers for solar cells and to identify CdS and TiO2 as sensible choices. The ionisation potential of GeS is found to be smaller than in comparable materials. Using XPS and hard x-ray photoemission (HAXPES) measurements in conjunction with density-functional theory calculations, we demonstrate that stereochemically active Ge 4s lone pairs are present at the valence-band maxima. Our work thus provides direct evidence for active lone pairs in GeS and GeSe, with important implications for the applications of these and related materials, such as Ge-based perovskites.

Diamond Keywords: Photovoltaics; Semiconductors

Subject Areas: Materials, Physics, Chemistry

Instruments: I09-Surface and Interface Structural Analysis

Added On: 23/09/2021 09:28


Discipline Tags:

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

Technical Tags:

Spectroscopy X-ray Photoelectron Spectroscopy (XPS) Hard X-ray Photoelectron Spectroscopy (HAXPES)