Core Levels, Band Alignments, and Valence-Band States in CuSbS₂ for Solar Cell Applications

Abstract

The earth-abundant material CuSbS (CAS) has shown good optical properties as a photovoltaic solar absorber material, but has seen relatively poor solar cell performance. To investigate the reason for this anomaly, the core levels of the constituent elements, surface contaminants, ionization potential, and valence-band spectra are studied by X-ray photoemission spectroscopy. The ionization potential and electron affinity for this material (4.98 and 3.43 eV) are lower than those for other common absorbers, including CuInGaSe (CIGS). Experimentally corroborated density functional theory (DFT) calculations show that the valence band maximum is raised by the lone pair electrons from the antimony cations contributing additional states when compared with indium or gallium cations in CIGS. The resulting conduction band misalignment with CdS is a reason for the poor performance of cells incorporating a CAS/CdS heterojunction, supporting the idea that using a cell design analogous to CIGS is unhelpful. These findings underline the critical importance of considering the electronic structure when selecting cell architectures that optimize open-circuit voltages and cell efficiencies.

Enhanced thermoelectric performance in polymorphic heavily Co-doped Cu2SnS3 through carrier compensation by Sb substitution

“…This indicates the intensified carrier scattering due to factors other than carrier interactions, which could be related with the decreasing fraction of c-CTS that has a higher σ than t-CTS [35]. Accordingly, the S values are enhanced as a result of the reduced n due to Sb doping, from ~54 μV K -1 for the x = 0 sample at 323 K to ~84 μV K -1 for the x = 0.08 one (see Figure 6 Actually, a similar effect has been clarified in CuSbS 2 [39], which would cause a net increase of density-of-states (DOS) near the Fermi level when the lone pair electrons first interact with S 3p electrons and the full antibonding orbital of this interaction is then sufficiently high so that it can subsequently interact with empty Sb 5p states, resulting in bonding states in the valence band and antibonding states at the bottom of the conduction band.…”

Copper antimony sulfide thin films for visible to near infrared photodetector applications

“…11 The bandgap obtained for CAS 20, 30 and 40 lms are 1.63, 1.58, 1.50 eV respectively. 43 The widest bandgap observed for 20 nm CAS lm might be due to the higher extent of unreacted Sb 2 S 3 present in it. Sanchez et al reported that the higher electron-hole pair generation and potent absorption coefficient resulted due to the direct band gap 44 which is suitable for the optoelectronic device applications.…”

High open‐circuit voltage CuSbS2 solar cells achieved through the formation of epitaxial growth of CdS/CuSbS2 hetero‐interface by post‐annealing treatment

“…On the other hand, the device structure of CuSbS 2 is directly inherited from CIGS counterpart. More study on the band alignment and interface defects of such heterojunction needs to be conducted . It is reported that CuSbS 2 and CdS could form a slight “cliff‐like” conduction band offset (CBO) by ultraviolet photoelectron spectroscopy analysis or even severe 0.85 eV “cliff‐like” CBO by X‐ray photoelectron spectroscopy characterization, neither of which falls within the favourable region of 0 to 0.4 eV “spike‐like” CBO and thereby causing large V oc deficit (E g /q – V oc ).…”