High Efficiency Dye-sensitized Solar Cells Constructed with Composites of TiO(2) and the Hot-bubbling Synthesized Ultra-Small SnO(2) Nanocrystals

An efficient photo-anode for the dye-sensitized solar cells (DSSCs) should have features of high loading of dye molecules, favorable band alignments and good efficiency in electron transport. Herein, the 3.4 nm-sized SnO(2) nanocrystals (NCs) of high crystallinity, synthesized via the hot-bubbling method, were incorporated with the commercial TiO(2) (P25) particles to fabricate the photo-anodes. The optimal percentage of the doped SnO(2) NCs was found at ~7.5% (SnO(2)/TiO(2), w/w), and the fabricated DSSC delivers a power conversion efficiency up to 6.7%, which is 1.52 times of the P25 based DSSCs. The ultra-small SnO(2) NCs offer three benefits, (1) the incorporation of SnO(2) NCs enlarges surface areas of the photo-anode films, and higher dye-loading amounts were achieved; (2) the high charge mobility provided by SnO(2) was confirmed to accelerate the electron transport, and the photo-electron recombination was suppressed by the highly-crystallized NCs; (3) the conduction band minimum (CBM) of the SnO(2) NCs was uplifted due to the quantum size effects, and this was found to alleviate the decrement in the open-circuit voltage. This work highlights great contributions of the SnO(2) NCs to the improvement of the photovoltaic performances in the DSSCs.