Cation disordering which arises from the size and chemical environment similarity of Cu and Zn, is the limiting factor in Cu2ZnSnSxSe4−x (CZTSSe) performance. Cation substitution is one effective way to solve this issue, however, the most commonly reported substitutes, Ag and Cd, are not ideal as they detract from the earth-abundant and non-toxic motivation of CZTSSe.
Mn is a promising candidate in comparison with other candidates (e.g. Fe, Ni or Co), because of its oxidation state stability and larger ionic size mismatch with Cu. In this study, Cu2MnxZn1-xSn(S,Se)4 (CMZTSSe) thin films solar cell were prepared by chemical spray pyrolysis and subsequently selenization process.
We study the influence of Mn substitution on the morphological, structural, optical, electrical and device performances. A distinct phase transformation from CZTSSe kesterite to C(M,Z)TSSe stannite is observed at 20% Mn substitution. High amount of Mn substitution (x ≥ 0.6) are shown to increase the carrier density significantly which introduce more defects and non-radiative carrier recombination as shown by quenched photoluminescence intensity. Consequently, reduction in device performances are observed from these samples. The highest power conversion efficiency is achieved at x ≈ 0.05 with η = 7.59%, Voc = 0.43 mV, Jsc = 28.9 mA/cm2 and FF = 61.03%.
The improved open circuit voltage (Voc) and fill factor (FF) are attributed to the improved shunt resistance and carrier transport due to less defects density especially in CdS/CMZTSSe interface. Finally, based on our electrical characterizations, a few suggestions to improve the efficiency are proposed.
Lie, S., Tan, J.M.R., Li, W., Leow, S.W., Tay, Y.F., Bishop, D., Oki, G. and Wong, L.H., 2017. Reducing interfacial defect density of CZTSSe solar cell by Mn substitution. Journal of Materials Chemistry A.
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Category: Solar & Photovoltaics