All-Vacuum-Deposited Bifacial Cu₂ZnSnSe₄ Photovoltaic Cells with Sputtered Cd-Free Buffer Layer

Figure 4

(a–d) Raman maps of the 1-cycle, 2-cycle, 3-cycle, and 4-cycle specimens, respectively. The scale bars in the figure are the Cu_xSe signal strength.

(a)

(b)

(c)

(d)