Stable SnSxSe1−x/CdS thin-film solar cells via single-source vapor transport deposition: unveiling band alignment at heterojunction interface

Abstract

SnSxSe1−x films can be fabricated by adjusting the Se/(Se + S) ratio by using two different source materials (SnS + SnSe or S + Se). However, maintaining a uniform composition throughout the film can be challenging when using conventional double-source methods. Here, we have developed a single-source vapor-transport-deposition (VTD) method to deposit highly compact and uniform SnSxSe1−x alloy films with a Se/(Se + S) compositional ratio of 0.3. Furthermore, we fabricate thin-film solar cell (TFSC) devices with varying evaporation durations ranging from 3 to 7 h. By increasing the evaporation duration from 3 to 7 h, the thickness of the SnS0.7Se0.3 absorber layer nearly doubled from around 1.05 µm to approximately 2.0 µm. As a result, the solar cell device (SLG/Mo/SnS0.7Se0.3/CdS/i-ZnO/AZO/Al) fabricated with a 5-h evaporation duration, which had an absorber thickness of approximately 1.55 µm and a bandgap of 1.18 eV, achieved a highest efficiency of 3.59%. In addition, its VOC, JSC, and FF were 0.284 V, 24.50 mA cm−2, and 51.3%, respectively. Furthermore, the band alignment at the SnS0.7Se0.3/CdS interface was investigated to determine the conduction band offset (CBO) and valence band offset (VBO). The results confirmed a cliff-like CBO of −0.07 eV at the SnS0.7Se0.3/CdS interface. The optimized device retained almost 99.9% of its initial efficiency after 6 months of storage in the air. © 2024 Elsevier B.V.