Spectroscopic analysis reveals distinct band offsets across buffer layers on Cu2ZnSnS4 heterojunctions, indicating that tailored hybrid buffers could resolve performance trade-offs.
Key Points
To measure the valence and conduction band alignments of CdS, Zn(O,S), and In2S3 buffer layers on Cu2ZnSnS4 absorber material to evaluate their impact on solar cell performance.
Determined valence band offsets of n-type CdS, Zn(O,S), and In2S3 buffers on p-type Cu2ZnSnS4 heterojunctions using X-ray Photoelectron Spectroscopy (XPS).
Measured conduction band offsets directly using Near Edge X-ray Absorption Fine Structure (NEXAFS) and calculated them indirectly from XPS data.
CdS formed a cliff-like conduction band offset with CZTS (CBOXPS = -0.24 ± 0.10 eV; CBONEXAFS = -0.18 ± 0.10 eV), whereas Zn(O,S) and In2S3 formed spike-like offsets (CBOXPS = 0.92 ± 0.10 eV and 0.41 ± 0.10 eV, respectively).
In2S3 buffers increased open circuit voltage compared to CdS, but the higher-than-optimal conduction band offset impeded electron flow, substantially lowering short circuit current and fill factor.