Electrodeposition of Simonkolleite as a Low-Temperature Route to Crystalline ZnO Films for Dye-Sensitized Solar Cells

A pulsed electrodeposition procedure has been developed to prepare macroporous films of the semiconducting mineral simonkolleite, Zn5(OH)8Cl2·H2O, on glass/FTO substrates. The morphology is characterized by the presence of smooth, micron-sized hexagonal platelets, and relatively thick films of 6 μm can be prepared in about 15 min. Simonkolleite can be transformed into crystalline, mesoporous ZnO using a relatively low temperature thermal treatment (250 °C). While the macrostructure of hexagonal platelets is maintained, they become mesoporous due to the removal of water and Cl−-containing reaction products. Dye-sensitized solar cells were fabricated with both simonkolleite and ZnO films, using the recently reported fully organic benzothiadiazole-based photosensitizer MG-207, and an electrolyte solution based on either the I−/I3 − or the Co(bpy)3 2+/3+ redox couple. An efficiency of 1.74% has been obtained for ZnO/MG-207/Co(bpy)3 2+/3+ solar cells, illustrating the promise of crystalline, mesoporous ZnO obtained via a low-temperature simonkolleite route for portable and lightweight devices based on flexible substrates.