Insights of Unconventionally Long Exposure Time in Atomic Layer Deposition Al₂O₃ to Modify SnO₂ Photoanode of Dye-Sensitized Solar Cells

Porous SnO₂ photoanodes coated by alumina through atomic layer deposition technology are reported. It is found that when the dosing time of precursor is extended over 11 s, the 125% maximum increase of cell efficiency is achieved. It is believed that besides the interfacial charge recombination being efficiently suppressed by this ultra-thin coating, the increased absorption of dyes and elimination of the high density of monoenergetic surface states on SnO₂ might play a positive role in improving the cell efficiency. The reason is that a long exposure time of precursor can guarantee the 100% coverage of alumina on porous SnO₂, which is further explained by a built three-step model. Then we conclude that for a high cell efficiency in porous photoelectrode a long exposure time is indispensable.