Synthesis of nano-TiO2 assisted by diethylene glycol for use in high efficiency dye-sensitized solar cells

The performance of dye-sensitized solar cells（DSSCs） consisting of anatase TiO_2 nanoparticles that were synthesized via a hydrothermal method was studied.The synthesized TiO_2 nanoparticles were characterized by X-ray diffraction（XRD）,nitrogen sorption analysis,scanning electron microscopy（SEM）,high resolution transmission electron microscopy（HRTEM）,and UV-vis spectroscopy.Then the J-Vcurve,electrochemical impedance spectroscopy（EIS）,and open-circuit voltage decay（OCVD） measurement were applied to evaluate the photovoltaic performance of DSSCs.Compared with the commercial TiO_2nanoparticles（P25）,the synthesized-TiO_2 nanoparticles showed better performance.By adding diethylene glycol（DEG） before the hydrothermal process,the synthesized TiO_2 nanoparticles（hereafter referred to as TiO_2-DEG particles） shows narrower size distribution,larger specific surface area,higher crystallinity,and less surface defects than TiO_2（DEG free） particles.The analysis of photovoltaic properties of DSSCs based on TiO_2-DEG particles showed that the recombination of electron-hole pairs was decreased and the trapping of carries in grain boundaries restrained.It was believed that the photoelectrode fabricated with the as-prepared TiO_2 nanoparticles improved the loading amount of dye sensitizers（N719）.and enhanced the photocurrent of the DSSCs.As a result,the TiO_2-DEG particle based cells achieved a photo-to-electricity conversion efficiency（η） of 7.90%,which is higher than 7.53%for the cell based on TiO2（DEG free） and 6.59%for the one fabricated with P25.