| Autor: |
Whittles TJ; Department of Physics and Stephenson Institute for Renewable Energy , University of Liverpool , Liverpool , L69 7ZF , U.K., Veal TD; Department of Physics and Stephenson Institute for Renewable Energy , University of Liverpool , Liverpool , L69 7ZF , U.K., Savory CN; Department of Chemistry , University College London , Christopher Ingold Building , London WC1H 0AJ , U.K.; Thomas Young Centre , University College London , Gower Street , London WC1E 6BT , U.K., Yates PJ; Department of Physics and Stephenson Institute for Renewable Energy , University of Liverpool , Liverpool , L69 7ZF , U.K., Murgatroyd PAE; Department of Physics and Stephenson Institute for Renewable Energy , University of Liverpool , Liverpool , L69 7ZF , U.K., Gibbon JT; Department of Physics and Stephenson Institute for Renewable Energy , University of Liverpool , Liverpool , L69 7ZF , U.K., Birkett M; Department of Physics and Stephenson Institute for Renewable Energy , University of Liverpool , Liverpool , L69 7ZF , U.K., Potter RJ; Department of Mechanical, Materials and Aerospace Engineering, School of Engineering , University of Liverpool , Liverpool , L69 3GH , U.K., Major JD; Department of Physics and Stephenson Institute for Renewable Energy , University of Liverpool , Liverpool , L69 7ZF , U.K., Durose K; Department of Physics and Stephenson Institute for Renewable Energy , University of Liverpool , Liverpool , L69 7ZF , U.K., Scanlon DO; Department of Chemistry , University College London , Christopher Ingold Building , London WC1H 0AJ , U.K.; Diamond Light Source Limited , Diamond House, Harwell Science and Innovation Campus , Didcot , Oxfordshire OX11 0DE , U.K.; Thomas Young Centre , University College London , Gower Street , London WC1E 6BT , U.K., Dhanak VR; Department of Physics and Stephenson Institute for Renewable Energy , University of Liverpool , Liverpool , L69 7ZF , U.K. |
| Abstrakt: |
The earth-abundant semiconductor Cu 3 BiS 3 (CBS) exhibits promising photovoltaic properties and is often considered analogous to the solar absorbers copper indium gallium diselenide (CIGS) and copper zinc tin sulfide (CZTS) despite few device reports. The extent to which this is justifiable is explored via a thorough X-ray photoemission spectroscopy (XPS) analysis: spanning core levels, ionization potential, work function, surface contamination, cleaning, band alignment, and valence-band density of states. The XPS analysis overcomes and addresses the shortcomings of prior XPS studies of this material. Temperature-dependent absorption spectra determine a 1.2 eV direct band gap at room temperature; the widely reported 1.4-1.5 eV band gap is attributed to weak transitions from the low density of states of the topmost valence band previously being undetected. Density functional theory HSE06 + SOC calculations determine the band structure, optical transitions, and well-fitted absorption and Raman spectra. Valence band XPS spectra and model calculations find the CBS bonding to be superficially similar to CIGS and CZTS, but the Bi 3+ cations (and formally occupied Bi 6s orbital) have fundamental impacts: giving a low ionization potential (4.98 eV), suggesting that the CdS window layer favored for CIGS and CZTS gives detrimental band alignment and should be rejected in favor of a better aligned material in order for CBS devices to progress. |
