Energy band alignment at the heterointerface between CdS and Ag-alloyed CZTS

Abstract

Energy band alignment at the heterointerface between CdS and kesterite Cu2ZnSnS4 (CZTS) and its alloys plays a crucial role in determining the efficiency of the solar cells. Whereas Ag alloying of CZTS has been shown to reduce anti-site defects in the bulk and thus rise the efficiency, the electronic properties at the interface with the CdS buffer layer have not been extensively investigated. In this work, we present a detailed study on the band alignment between n-CdS and p-CZTS upon Ag alloying by depth-profiling ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). Our findings indicate that core-level peaks and the valence band edge of CdS exhibit a significant shift to a lower energy (larger than 0.4 eV) upon the etching of the CdS layer, which can be assigned due to band bending and chemical shift induced by a change in the chemical composition across the interface. Using a simplified model based on charge depletion layer conservation, a significantly larger total charge region depletion width was determined in Ag-alloyed CZTS as compared to its undoped counterpart. Our findings reveal a cliff-like band alignment at both CdS/CZTS and CdS/Ag-CZTS heterointerfaces. However, the conduction-band offset decreases by more than 0.1 eV upon Ag alloying of CZTS. The approach demonstrated here enables nanometer-scale depth profiling of the electronic structure of the p–n junction and can be universally applied to study entirely new platforms of oxide/chalcogenide heterostructures for next-generation optoelectronic devices.

Dangling Bond-Induced Surface Depletion in CdS Leaf

“…Figure shows the valence band spectra of the leaf structure of CdS measured at different take-off angles. The data obtained at the take-off angle of 0° show that the main Cd 4d peak appears at 11.2 eV, which matches with the reported data of CdS . In addition, we observed that a shoulder appeared at higher binding energy.…”

“…The data obtained at the take-off angle of 0°show that the main Cd 4d peak appears at 11.2 eV, which matches with the reported data of CdS. 44 In addition, we observed that a shoulder appeared at higher binding energy. Further, the features of the Cd 4d peak measured at different take-off angles indicate that the intensity of the main peak gradually decreases and that of the shoulder peak increases with increasing take-off angle.…”

Mechanism‐Based Approach of CdS/Cu(In,Ga)Se2 (CIGS) Interfaces for CIGS Solar Cells through Deposition in Different Stages of Continuous Chemical Bath Deposition Reaction: Key to Achieving High Photovoltaic Performance

“…Figure 17 shows the schematic band alignments of the CIGS/ CdS interface for the 30 and 60 nm CdS thin films considering the approximate band bending by Cd diffusion. [43][44][45][46] To investigate the schematic changes in the band alignment by thickness with and without HT, the mean ΔE C change of the band alignment for the 30 nm CdS layer was exhibited. The band alignment here is based on the CBM calculated by UPS and UV measurements as mentioned earlier, so it is approximate alignment compared to the CBM values obtained by IPES measurements.…”

Recent Progress of Critical Interface Engineering for Highly Efficient and Stable Perovskite Solar Cells

“…However, this is not always the case when the ETL layer is thin enough (e.g., < 5nm), because tunneling effect might assist the current flow through the interface, as Type I heterojunction is prevalent in Cu(In,Ga)Se 2 and Cu 2 ZnSnS 4 solar cells. [ 23–25 ] Type I band alignment can effectively prevent the interface recombination due to a large distance between E c of ETL and E v of perovskite. Nevertheless, it is reported that in‐situ growth of a high band gap interlayer in the HTL/perovskite interface can improve the V oc substantially, which is mainly due to the Type I band alignment formed in the interface.…”