Highly improved light harvesting and charge separation of TiO2/N719 photoanodes using surface NiTiO3 quantum dot decoration

Abstract

Conventional TiO2/N719 photoanodes often suffer from the limited visible light absorption (450–500 nm) and the serous recombination of photo-generated carries (e−/h+)/electrolyte ions (I3−), accordingly outputting a low photoelectronic conversion efficiency (PCE). In this work, a type of strawberry-like TiO2/NiTiO3 (NTO) nanospheres was designed via a simple hydrothermal method. In this design, the NTO quantum dots (QDs) with size of several nanometers were decorated on the surface of TiO2 nanospheres. This TiO2/NTO nanostructure can not only enhance the visible light absorption of the TiO2/N179 photoanodes but also improve the separation of photo-generated carriers and depress the recombination of e−/h+ and I3−. Thus, the optimal TiO2/NTO/N719 dye-sensitized solar cells (DSSCs) achieved greatly improved Jsc and Voc, both of which result into a 32.8%-improved PCE compared to the TiO2/N719 ones. These improvements could be due to the decreased charge transfer resistance at the photoanode/electrolyte interface (Rct2) and the increased electron lifetime (τn) caused by TiO2/NTO hetero-interface. In addition, the optimization on NTO QDs indicates that the density of QDs main affects the τn, and the size of QDs affects with Rct2. Moderate density and size (ca. 5 nm) of QDs can optimize the photoelectronic performances of DSSCs.