Identify the Origin of the Voc Deficit of Kestertie Solar Cells from the Two Reaction Paths Induced by Sn2+ and Sn4+ Precursors in DMSO Solution

The reaction paths and device characteristics of the two Cu
2
ZnSn(S,Se)
4
absorbers fabricated from DMSO solution respectively using Sn
²⁺
and Sn
⁴⁺
as tin precursor were systematically investigated to identify the large voltage deficit issue that limits kesterite solar cell performance. Our results show Sn
²⁺
precursor film took a multi-phase fusion reaction path and forms in a very defective surface whereas Sn
⁴⁺
precursor film took a direct transformation reaction path and forms a uniform and less defective surface. The much larger V
oc
deficit of Sn
²⁺
device mainly comes from the deep defect rich surface due to its unfavorable grain growth.