Alkali-Templated Surface Nanopatterning of Chalcogenide Thin Films: A Novel Approach Toward Solar Cells with Enhanced Efficiency

Concepts of localized contacts and junctions through surface passivation layers are already advantageously applied in Si wafer-based photovoltaic technologies. For Cu­(In,Ga)­Se₂ thin film solar cells, such concepts are generally not applied, especially at the heterojunction, because of the lack of a simple method yielding features with the required size and distribution. Here, we show a novel, innovative surface nanopatterning approach to form homogeneously distributed nanostructures (<30 nm) on the faceted, rough surface of polycrystalline chalcogenide thin films. The method, based on selective dissolution of self-assembled and well-defined alkali condensates in water, opens up new research opportunities toward development of thin film solar cells with enhanced efficiency

Enhanced Carrier Collection from CdS Passivated Grains in Solution-Processed Cu₂ZnSn(S,Se)₄ Solar Cells

Solution processing of Cu₂ZnSn­(S,Se)₄ (CZTSSe)–kesterite solar cells is attractive because of easy manufacturing using readily available metal salts. The solution-processed CZTSSe absorbers, however, often suffer from poor morphology with a bilayer structure, exhibiting a dense top crust and a porous bottom layer, albeit yielding efficiencies of over 10%. To understand whether the cell performance is limited by this porous layer, a systematic compositional study using (scanning) transmission electron microscopy ((S)­TEM) and energy-dispersive X-ray spectroscopy of the dimethyl sulfoxide processed CZTSSe absorbers is presented. TEM investigation revealed a thin layer of CdS that is formed around the small CZTSSe grains in the porous bottom layer during the chemical bath deposition step. This CdS passivation is found to be beneficial for the cell performance as it increases the carrier collection and facilitates the electron transport. Electron-beam-induced current measurements reveal an enhanced carrier collection for this buried region as compared to reference cells with evaporated CdS