Simulations of photocurrent improvement through combined geometric/diffracting light trapping in organic small molecule solar cells

Abstract

Although organic solar cells have recently shown remarkable high power conversion efficiencies approaching 12%, further improvements are needed to become a low cost alternative to current inorganic photovoltaic technologies. Optical losses due to insufficient light trapping, parasitic absorption in the contact layers and reflectance limit drastically the photocurrent delivered by these solar cells. In this work, we simulated two- (2D) and three-dimensional (3D) surface textures in the micro- and submicroscale to improve light trapping in optimized organic solar cells based on copper phtalocyanine (CuPc) and fullerene (C60). The analysis was carried out with the aid of the finite elementmethod in 2Dand 3D, taking into account interference as well as reflection and diffraction of the incidentAM1.5 spectrum. At normal incidence, up to 23% improvement in the photocurrent over the planar cell was obtained. To investigate the texture performance under practical circumstances, we simulated 2D microstructures during a typical summer day, taking the change of incidence angle and radiation intensity into account. Results clearly showthat all textured cells delivermore photocurrent than the planar cell, even at oblique angles.