Controlling the microstructure and properties of titania nanopowders for high efficiency dye sensitized solar cells

A low temperature hydrothermal process have been developed to synthesize titania nanorods (NRs) and nanoparticles (NPs) with controlled size for dye sensitized solar cells (DSSCs). Effect of calcination temperature on the performance of TiO₂ nanoparticles for solar cells was investigated and discussed. The crystallite size and the relative crystallinity of the anatase phase were increased with increasing the calcination temperature. The structures and morphologies of both (TiO₂ nanorods and nanoparticles) were characterized using XRD, SEM, TEM/HRTEM, UV-vis Spectroscopy, FTIR and BET specific surface area (S_BET) as well as pore-size distribution by BJH. The size of the titania nanorods was 6.7 nm width and 22 nm length while it was 13 nm for nanoparticles. Efficiency of dye-sensitized solar cells (DSSCs) fabricated with oriented TiO₂ nanorods was reported to be more superior compared to DSSC based on mesoporous TiO₂ nanoparticles due to their high surface area, hierarchically mesoporous structures, low charge recombination and fast electron-transfer rate. With increasing calcination temperature of the prepared nanopowders, the light-electricity conversion efficiency (η) decreased. The efficiency of the assembly solar cells was decreased due to the agglomeration of the particles and difficulty of electron movement. The power efficiency was enhanced from 1.7% for TiO₂ nanoparticles cells at hydrothermally temperature 500 °C and 5.2% for TiO₂ nanoparticles cells at hydrothermally temperature 100 °C to 7.2% for TiO₂ nanorods cells under AM1.5 illumination (100 mW cm ^-2).