Improving the efficiency of dye-sensitized solar cells with ultrasonic spray-coated TiO2 electrode that was modified by MnO2, CoO, or SnO2

Abstract

This research investigated the modification of TiO2 electrode by adding the second metal oxide, namely, manganese dioxide (MnO2), cobalt oxide (CoO), or tin dioxide (SnO2) use in for dye-sensitized solar cell (DSSCs). TiO2 and modified TiO2 sols were synthesized via sol-gel methods. The sols were sprayed 500 times onto the fluorine-doped tin oxide glass substrates as a thin film using an ultrasonic spray coater. Finally, the thin film electrode was calcined at 400ºC for two hours. The amount of MnO2, CoO, or SnO2 was varied at 0, 0.1, 0.5, 1.0, and 3.0%wt. The photovoltaic efficiency of DSSCs was measured using an IV-tester under a light irradiance of 15 mW/cm2. The dye sensitizer used was ruthenium-based N719 dye and the electrolyte solution composed of lithium iodide (LiI), iodine (I2), and 4-tert-butylpyridine (4-TBP) in acetonitrile with a molar ratio of LiI:I2:4-TBP of 0.1:0.01:0.1. The efficiency of DSSCs with pure TiO2 electrode was 3.12±0.32% with optimum loading of MnO2, CoO, and SnO2 with 0.5, 0.1, and 0.5%wt, respectively, the efficiency of DSSC rose to 4.83±0.36%, 3.23±0.40%, and 6.68±0.43%, respectively. This was pattly attributed to the large amount of ruthenium dye molecule adsorbed on the electrode. In addition, both short circuit current density (JSC) and open circuit voltage (VOC) were improved, resulting in greater efficiency of DSSCs with the single-layered electrode. Next, the thin films double-layered electrode with pure TiO2 as the under layer and 0.5%wt. SnO2/TiO2 as the over layer was employed. The cell efficiency rose from 6.68±0.43% to 8.72±0.31%, compared with the single-layered electrode with 0.5%wt. SnO2 because of enhanced light scattering inside the DSSC from the mismatched crystallite size of TiO2.