N-Ion-implanted TiO₂ photoanodes in quantum dot-sensitized solar cells

Hierarchical nanostructured titanium dioxide (TiO₂) clumps were fabricated using electrostatic spray with subsequent nitrogen-ion doping by an ion-implantation technique for improvement of energy conversion efficiency for quantum dot-sensitized solar cells (QDSCs). CdSe quantum dots were directly assembled on the produced N-ion-implanted TiO₂ photoanodes by chemical bath deposition, and their photovoltaic performance was evaluated in a polysulfide electrolyte with a Pt counter electrode. We found that the photovoltaic performance of TiO₂ electrodes was improved by nearly 145% upon N-ion implantation. The efficiency improvement seems to be due to (1) the enhancement of electron transport through the TiO₂ layer by inter-particle necking of primary TiO₂ particles and (2) an increase in the recombination resistance at TiO₂/QD/electrolyte interfaces by healing the surface states or managing the oxygen vacancies upon N-ion doping. Therefore, N-ion-doped photoanodes offer a viable pathway to develop more efficient QD or dye-sensitized solar cells.