Performance improvement of ultrathin organic solar cells utilizing light-trapping aluminum-titanium nitride nanosquare arrays

Despite the crucial role of plasmonic nanostructures in enhancing the performance of organic solar cells, the actual absorption of the active layer in these cells is restricted by the parasitic metal absorption loss limiting their efficiencies. In this paper, a bilayer of Al-TiN nanosquare array has been proposed as a novel plasmonic scheme in order to improve the photocurrent and the solar absorption of organic solar cells. The hybrid design of Al and TiN materials reduces the parasitic loss issue offering extended application of plasmonic light-harvesting structures. Engineering the energy band diagram of the cell and concentrating the electrical field distribution inside the active layer result in boosting the absorption as well as the optical current densities for each layer. Utilization of TiN in the proposed design also benefits from the cost effectiveness, abundance, and CMOS compatibility of this material compared to noble metals as well as featuring appropriate light trapping properties. In addition, the symmetric scheme of the proposed structure makes it polarization insensitive under the normal incidence. The numerical simulations of this study based on the finite-difference time-domain (FDTD) method show an enhanced absorption of 70-88% over the spectral range of 300-625 nm and the maximum enhancement factor of 2.16 at the wavelength of about 665 nm. Moreover, an improved photocurrent density of 13.7082 (mA/cm2) has also been achieved despite the usage of an ultrathin active layer. The proposed design can also be developed to achieve performance enhancement of other thin film solar cells in the future.