Enhanced electron lifetime in CdS quantum dot-sensitized solar cells with nanoporous-layer-covered TiO₂₊ nanotube arrays

CdS quantum dots (QDs) of 6.8-6.9 nm were assembled in situ on conventional TiO₂₊ nanotube arrays (Type I) and nanoporous-layer-covered nanotube arrays (Type II). The QD-sensitized solar cell with the Type II nanotubes exhibited significantly enhanced overall energy conversion efficiency, despite having less assembled QDs. This was due to the Type II nanotube arrays having fewer defects and suppressed recombination rate (or back electron transport) from surface traps in the TiO₂₊ to electron traps in the QDs, resulting in significantly improved electron lifetime.