High-yield synthesis of “oriented attachment” TiO2 nanorods as superior building blocks of photoanodes in quantum dot sensitized solar cells

Abstract

In this paper, a high-yield hydrothermal synthesis of “oriented attachment” TiO₂ nanorods (TiO₂-NRs) and their application as a superior photoanode material in a quantum-dot (QD) sensitized solar cell have been reported. The NRs' morphology could be finely tuned by the concentrations of titanium isopropoxide, and tetramethylammonium hydroxide, and their relative molar ratios. The production yield of TiO₂-NRs with the fine size of 18 nm × 150 nm could be as high as 20 grams per one reaction from a 500 mL autoclave. These NRs, as building blocks of photoanodes in CdSe QD sensitized solar cells, are found to be superior to traditionally used TiO₂ nanoparticles, which is reflected in the following aspects: (1) the resultant TiO₂ mesoporous film possesses a wider pore size distribution, which allows a higher loading content of QDs and fluent electrolyte diffusion; (2) the as-built quasi-one dimensional network with limited grain boundaries possesses a higher electron diffusion coefficient and longer electron lifetime. As a consequence of these, synchronized improvements on photocurrent, photovoltage and fill factor have been achieved, leading to a dramatic elevation of the overall solar conversion efficiency. Finally, in combination with a highly efficient catalytic counter electrode made of Cu₂ZnSnS(Se)₄ nanocrystals, the best cell efficiency reached 5.96%, which is comparable to the best-in-class devices reported to date.