Effect of hexamethylenetetramine on the properties of electrodeposited ZnO thin films for dye sensitized solar cell applications

Zinc oxide (ZnO) thin films were obtained on fluorine doped tin oxide substrates by pyrolyzing the electrodeposited zinc hydroxide chloride thin films. The effect of hexamethylenetetramine (HMTA) concentrations on the structural, morphological, vibrational and optical properties was investigated. The ZnO growth orientation is changed from (101) to (002) plane as the HMTA concentrations get increased from 0 to 9 mM. The well-defined hexagonal nanorods and nanowires structures are observed for ZnO thin films deposited in the absence and presence of HMTA. The increase in intensity of E₂ (high) vibrational mode, near band edge emission and UV absorbance confirms the ZnO nanowires synthesized in the solution containing 9 mM HMTA having better crystallinity, lesser atomic defects and higher dye loading, respectively. The efficiency of dye sensitized solar cells (DSSCs) based on nanorods and nanowires synthesized in the solutions containing 0 and 9 mM HMTA is 0.36 and 1.02%, respectively. The DSSC based on nanowires photoanode has a higher R_rec, τ_n, σ_n and L_n than another DSSC.