Since its discovery, dye-sensitized solar cell (DSSC) has attracted great attention owing to their low cost and potentially high power-conversion efficiencies. Despite the substantial progress made so far, further improvement is necessary for DSSCs to compete with other photovoltaic devices and to enter the commercial market. The solar cell should be thin enough to ensure all the carriers are collected but also be thick enough to absorb more light. The optical path length should be extended as much as possible to solve this seemingly contradictory problem. The light harvest in a solar cell can be greatly improved if the sunlight is made obliquely incident into the absorption layer. Not only enhancing absorption by increasing the optical path length, this configuration is also favorable for the extraction of charges as they are generated closer to the collecting electrode. Despite many advantages, the deflection of incident light has not been implemented for DSSC because of the inherent difficulty of incorporating a relevant structure. Our approach is to generate a refractive-index grating in the bottom of TiO2 absorption layer so that the incident light can be widely spread by diffraction. We have successfully fabricated DSSCs embedded with a diffraction grating of 2 mm period via imprinting combined with TiCl4 treatment. As a result, the IPCE and current density of the cell were much improved. The relevant work has been published in Adv. Energy Materials and J. Materials Chemistry C (as the cover-page paper). This facile approach can be effectively utilized to increase the light harvest of DSSC and its energy conversion efficiency. Our ultimate goal is to embed a nano-scale grating so that the incident light can be confined within the absorption layer by total internal reflection. In this case, the optical path length can be increased infinitely.
(Adv. Energy Mater. 2014, 4, 1300978 & J. Mater. Chem. C 2014, 2, 981)