The effect of AZO and compact TiO2 films on the performance of dye-sensitized solar cells

• Post-annealing treatment decreases the AZO films' resistivity.
• After UV irradiation, the compact TiO2 layer is ultra-hydrophilic.
• The compact TiO2 layer thickness affects the conversion efficiency of the DSSC.
• The Taguchi method offers an efficient way to increase experimental efficiency.

This paper presents a scheme that produces the optimal deposition parameters for inexpensive Al-doped zinc oxide (AZO, transparent conducting oxide) films and compact TiO2 layers. This scheme improves the performance of dye-sensitized solar cells (DSSC) that are produced by radio frequency (rf) magnetron sputtering onto soda-lime glass substrates. The results show that using the grey relational Taguchi method, the electrical resistivity of AZO films is reduced from 6.2 to 3.4 × 10− 3 Ω-cm and the visible range optical transmittance is changed, from 88.7 to 88.8%. The (002) diffraction peaks for the AZO films are sharper and their full width at half maximum is narrower, which demonstrates that the crystalline structure of the AZO films is improved. Post-annealing increases the grain size of the AZO films, which leads to further decreased resistivity from 3.4 to 1.72 × 10− 3 Ω-cm because there is an increase in the carrier concentration and the Hall mobility. A compact TiO2 layer is achieved using rf sputtering deposition and the effect of the thickness (40, 70, 100 150 and 200 nm) on the DSSC conversion efficiency is determined. The effect of TiO2 compact layer prevents electron transport to the electrolyte and a higher short-circuit current density will be obtained. The experimental results show that the DSSC conversion efficiency is critically affected by the thickness of the compact TiO2 layer, and the thickness of compact layer is about 100 nm will leads to the optimal efficiency.

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