Harnessing the Potential of Porous ZnO Photoanodes in Dye-Sensitized Solar Cells by Atomic Layer Deposition of Mg-Doped ZnO

Mg-doped ZnO (MZO) photoanodes in dye-sensitized solar cells (DSSCs) are intended to increase the open-circuit voltage VOC and boost the power conversion efficiency. However, unintended side effects of the Mg incorporation into ZnO, such as increased transport resistance and recombination rate, commonly outweigh the benefits by reducing the short-circuit current JSC. In this work, we resolve this issue by synergizing the large band-gap energy of MZO with the fast electron transport of ZnO, thus significantly increasing the power conversion efficiency. Atomic Layer Deposition enables the successful fabrication of the required core–shell structures consisting of pure nanoparticulate ZnO films as cores with homogeneous MZO shells. We find a significant increase of the open-circuit voltage, while largely avoiding losses of the short-circuit current. The transport resistance in the cells slightly decreases up to 10 at. % Mg in the shells, and it increases only slightly for Mg concentrations as high as 20 at. %. Our work demonstrates the advantages of mixed architectures consisting of a pure matrix modified by a well-controlled thin active layer. Optimization of cells with such high photovoltages offers a promising pathway toward significantly improved concepts for DSSCs