Junction formation of Cu₃BiS₃ investigated by Kelvin probe force microscopy and surface photovoltage measurements

Abstract

SummaryRecently, the compound semiconductor Cu3BiS3 has been demonstrated to have a band gap of ~1.4 eV, well suited for photovoltaic energy harvesting. The preparation of polycrystalline thin films was successfully realized and now the junction formation to the n-type window needs to be developed. We present an investigation of the Cu3BiS3 absorber layer and the junction formation with CdS, ZnS and In2S3 buffer layers. Kelvin probe force microscopy shows the granular structure of the buffer layers with small grains of 20–100 nm, and a considerably smaller work-function distribution for In2S3 compared to that of CdS and ZnS. For In2S3 and CdS buffer layers the KPFM experiments indicate negatively charged Cu3BiS3 grain boundaries resulting from the deposition of the buffer layer. Macroscopic measurements of the surface photovoltage at variable excitation wavelength indicate the influence of defect states below the band gap on charge separation and a surface-defect passivation by the In2S3 buffer layer. Our findings indicate that Cu3BiS3 may become an interesting absorber material for thin-film solar cells; however, for photovoltaic application the band bending at the charge-selective contact has to be increased.

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

“…Peaks from carbon and oxygen are also present; not unexpected because of hydrocarbon contamination from exposure to atmosphere, which then subsequently reduced after cleaning. Sodium was also found, which did not decrease on cleaning, suggesting that the sodium has diffused through from the glass, as has been seen in similar materials 56 . Further discussion of the nature and effects of sodium with the corresponding spectra can be found in the SI.…”

A comprehensive review on synthesis and characterizations of Cu3BiS3 thin films for solar photovoltaics

“…Numerous evaporation methods such as coevaporation, fast evaporation, thermal evaporation, and electron beam (EB) [21][22][23][24][25][26][27][28][29][30][31][32] have been employed for the deposition of Cu 3 BiS 3 thin films. Cu 3 BiS 3 thin films were deposited using two different attitudes:…”

“…Later on, Mesa et al [25] investigated the formation of ZnS, In 2 S 3 , and CdS buffer layers on Cu 3 BiS 3 for application as an absorber layer in solar cell. The Cu 3 BiS 3 and ZnS (thickness 200 nm) thin films were deposited by the co-evaporation techniques reported previously [23,26].…”

Copper—antimony and copper—bismuth chalcogenides—Research opportunities and review for solar photovoltaics

“…Further studies of the roles of heterojunctions and grain boundaries in Cu 3 BiS 3 are reported by Mesa, 116 who measured the surface electronic properties of NH 3 -cleaned Cu 3 BiS 3 films and also with overlayers of CdS, ZnS, and In 2 S 3 using Kelvin probe microscopy and surface photovoltage measurements. While the grain boundaries in the Cu 3 BiS 3 itself were found to be positively charged, a different behavior was seen when there was an over-layer of either CdS or In 2 S 3 (but not ZnS): the more positive work function at the positions of the grain boundaries in the underlying Cu 3 BiS 3 was taken as evidence that the over-layers changed the grain boundary charge state from negative to positive.…”