Influence of silver introduction into (Ag,Cu)(In,Ga)S2 thin films on their physical properties

Silver was introduced into pure-sulfide Cu(In,Ga)S2 (CIGS) to form (Ag,Cu)(In,Ga)S2 (ACIGS) compound. The impact of the Ag addition on physical properties and photovoltaic performances was therefore examined to determine suitable Ag amount in ACIGS solar cells. The ACIGS thin films with different Ag/(Ag + Cu) (AAC) compositional ratios were formed through the sulfurization of the In/Cu/Ga/Ag stacked precursors. It is disclosed that the AAC is obviously increased from 0 to 0.18 under the increase in the Ag precursor thickness from 0 to 80 nm. Moreover, under the suitable Ag introduction (ACC of 0.04), the quality of ACIGS absorbers is improved with low Urbach energy (EU) and the enlargement of crystal grain size. The decreased conduction band offset between the absorber and CdS buffer layers under Ag addition is realized with lower valence band maximum value of the ACIGS absorbers, thus feasibly increasing the hole barrier. Additionally, the band alignment between absorber and CdS buffer layers was disclosed with the varied ACC based on photoemission yield spectroscopy. Ultimately, the short-circuit current density of the ACIGS solar cell is clearly increased by 2 mA/cm2 under suitable ACC of 0.04.