Extrinsic doping of the Cu2ZnSn(S,Se)4 (CZTS) absorber layers in thin film photovoltaics with Group I ions has been shown to increase overall device performance.  However, the origin of this enhancement in power conversion efficiency is not well understood.  We use scanning probe microscopy (SPM) to characterize the changes in electrical properties and morphology of CZTS thin films fabricated using solution-processed molecular precursors.  Topographical data from SPM show that films prepared with Group I dopants exhibit less microstructural heterogeneity compared to devices with no doping or minimal doping.  Furthermore, Scanning Kelvin Probe Microscopy (SKPM) imaging shows that the sign of the contact potential difference inverts at the grain boundaries upon doping, an effect which correlates with a change in microstructure. Finally, conductive atomic force microscopy (cAFM) images show greater surface conductivity in doped absorber layers. We correlate SKPM and cAFM images to provide new insight into how Group I doping changes both potential and conductivity at the grain boundaries versus bulk material, providing an explanation for the improved device performance.

Group I doping improves power conversion efficiency of Cu<sub>2</sub>ZnSn(S,Se)<sub>4</sub>  absorber material

248th National Meeting (2014)

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Group I doping improves power conversion efficiency of Cu2ZnSn(S,Se)4 absorber material

Group I doping improves power conversion efficiency of Cu₂ZnSn(S,Se)₄ absorber material