Abstract
The study on the anion effect of different Zn sources—Zn, ZnCl2, ZnI2, Zn and ZnSO4—on the chemical deposition of ZnS(O,OH) films revealed that the growth rate and composition of the ZnS(O,OH) layer depend on the instability constant (pK) value of the corresponding Zn‐complex Zn(L) n in the chemical bath solution. In the region of pKZn(NH3)2+ > pKZn(L)n the ZnS(O,OH) film′s growth rate and ZnS concentration in films increased with the increasing pK value of the used Zn salt complex up to the pK value of the complex and decreased in the region where pKZn(NH3)2+ < pKZn(L)n. The band gap values (around 3.6 eV in most cases) of deposited ZnS(O,OH) films did not depend on the Zn precursor′s instability constant, the ZnS(O,OH) film from zinc nitrate containing bath has higher band gap energy (Eg = 3.8 eV). The maximum efficiency of CISSe and CZTSSe monograin layer solar cells was gained with ZnS(O,OH) buffer layer deposited from CBD solution containing Zn as Zn source, which provided the highest growth rate and ZnS concentration in the ZnS(O,OH) film on glass substrates.
Highlights
ZnS is beside CdS the second most investigated buffer layer material for CuInSe2 (CISe) type solar cells
Khallaf et al [8] found that higher values of instability constants of the different cadmium complexes in the deposition solution led to the thinner CdS films
Current densities of chemical bath deposition (CBD)-ZnS/Cu(In)Se2 monograin layer solar cells changed with instability constants of Zn-ligand complexes following the same law as that of the growth rate of ZnS(O,OH) films (Figure 4)
Summary
ZnS is beside CdS the second most investigated buffer layer material for CuInSe2 (CISe) type solar cells. A chemical bath deposition (CBD) is the most commonly used process for ZnS buffer formation on the top of a CISe type absorber. A change in the electrical resistivity, growth rate and particle size of the films with changes in chemical nature of anions in chemical bath solution was detected, but those changes did not lead to the changes in efficiencies of CISe solar cells [9]. The growth rate of the films along with compositional and optical properties presented together with photovoltaic characteristics of CuIn(S,Se) (CISSe), and Cu2ZnSn(S,Se) (CZTSSe) monograin layer (MGL) solar cells with CBD ZnS(O,OH) buffer layers
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