Broadband absorption of modified conical nanowires for photovoltaic applications

In this paper, modified conical nanowires (CNWs) with different top diameters are suggested to break the structure mirror symmetry and increase the light absorption. The proposed arrange-ment consists of 2 x 2 periodic CNWs with top different conical diameters where the light reflection is reduced and therefore the absorption efficiency is enhanced. The optical character-istics of the suggested CNWs are numerically simulated using three-dimensional 3-D finite -difference time-domain (FDTD) method. The numerical results show that a good coupling of the scattered light is achieved through the proposed NWs with multiple resonant wavelengths. In this context, the Mie resonances are improved and strengthened over a wide range of wavelengths by optimizing the top cone diameters. The reported design offers an ultimate efficiency (eta) of 39.8 % and short circuit current density (Jsc) of 35.2 mA/cm2 with an enhancement of 28.8 % compared to the conventional CNWs. When a bottom Si substrate and Ag back reflector are used, the eta and Jsc are improved to 42.1 % and 37.4 mA/cm2, respectively. This is owing to the coupling between the supported modes in the NWs and those excited in the Si substrate. The maximum power conversion efficiency (PCE) in the axial junction of the modified CNWs structure is equal to 18 % compared to 15.5 % for the conventional CNWs design with an enhancement of 16 % in the ideal passivation.