Efficiency enhancement in dye-sensitized solar cells using hierarchical TiO2 submicron size spheres as a light scattering layer

Abstract

The photoanode of a dye-sensitized solar cell (DSSC), usually made with a nanoporous TiO2 semiconductor layer sensitized with N719 dye, plays a crucial role in the overall power conversion efficiency as it influences both the light absorption and the electron transport. Generally, enhanced photon absorbance is achieved through light scattering in the device by employing a double layered TiO2 photoanode consisting of an active layer of smaller (~ 20 nm) P25 particles and a scattering layer consisting of larger (~ 300 nm) particles. However, due to the smaller effective surface area of the larger particle layer, the dye adsorption in the second layer is very poor, and therefore, the efficiency enhancement due to the usage of thicker photo anode is hindered. Therefore, in this study, investigations were carried out to replace the conventional, larger particle scattering layer by a morpho logically different structure of TiO2. Here, the DSSC performance between two different types of scattering layers, one consisting of TiO2 nanorods (NRs) and the other consisting of hierarchically structured TiO2 submicron size spheres (MS) are compared. DSSC fabricated with P25/MS double-layered photoanode outperforms the DSSC fabricated with P25/NR double-layered photoanode. P25/MS-based DSSC delivered a highest short-circuit current density of 14.80 mA cm−2 with an efficiency of 7.38%, while the efficiency of DSSC fabricated with P25/NR photoanode exhibits 7.03% efficiency. The DSSC fabricated without a scattering layer showed only 6.68% efficiency. The diffuse reflectance and dye adsorption measurements revealed that the better performance of P25/MS double-layered DSSC is largely due to the improved photon absorption facilitated by superior light scattering as well as higher dye loading by TiO2 submicron size spheres.