An investigation of the photovoltaic parameters of ZnS grown on ZnO(101)

Abstract

In the present work, a relationship between the pencil-like growth of wurtzite zinc oxide (ZnO) with specific surfaces to support zinc sulfide (ZnS) deposition and its photovoltaic behavior is proposed. The wurtzite ZnO and zinc blende ZnS were explored in the context of the ZnO/ZnS interfaces obtained from zinc acetate (ZA) and zinc nitrate (ZN). A more effective ZnS coating was obtained on polar (101) ZnO surfaces, using ZN precursors, since the growth of planes is electronically and sterically favored because of the accentuated charge polarization. The hexagonal rod shaped ZnO with pencil-like end was examined by scanning electron microscopy, its surface stability was confirmed by density functional theory, and the shape change diagram obtained from the classic Wulff construction demonstrated that the (100) and (101) ZnO planes have increased energetic stability. From photovoltaic measurements we observed improvements in the ZnO/ZnS (ZN) (i) photocurrent density, from 0.88 to 1.03 mA cm⁻², corresponding to an increment of 17%; (ii) open-circuit photovoltage, from 0.62 to 0.67 V, equivalent to an increment of 8%; and (iii) photoconversion efficiency, from 0.40 to 0.42%, representing an improvement of 4.7% in the case of the predominant (101) plane growth. On the other hand all ZnO/ZnS systems have the same main absorption bandgap of 3.1 eV. Significantly, this data set demonstrates that better photovoltaic behavior can be achieved in ZnO/ZnS (ZN) through covering and surface growth control, resulting in adequate band alignment.