Nanoscale dimples for improved absorption in organic solar cells

Organic solar cells (OSC’s) have attracted much attention in the past years due to their potential low-cost, light-weight and mechanical flexibility. A method for improving the power conversion efficiencies of the devices is by incorporating structured electrodes in the solar cell architecture, as they can improve light absorption in the active layers of the devices. In this direction, a cheap and large-scale compatible method for structuring the electrodes in OSC’s is by the use of Anodic Alumina Oxide (AAO) membranes.
In the present work, Al films of high purity and low roughness are formed via e-beam evaporation of few nanometers of Al followed by a micrometer layer of Al via sputter deposition. The samples are then anodized to form nano-scale pores of controlled sizes. The anodization of the prepared samples occurs in an electrochemical cell in H2SO4, H2C2O4 and H3PO4 solutions, different electrolyte solution and control of anodization parameters (sample temperature, voltage) allows the tuning of the AAO pore diameter and interpore distance.
Subsequently, the fabricated AAO is selectively etched in H2CrO4/H3PO4 mixtures, in order to reveal the underlying Al nanoscale dimples, which are present at the bottom of the pores. The dimples are then covered with a thin layer of PMMA and the impact from different dimple dimensions is investigated experimentally via ablation experiments and through simulations conducting FDTD studies that complement the experimental findings. In addition a comparison between ordered and discorded dimple arrangement and their contribution to light management is presented. Such dimples can later be employed to fabricate nanostructured electrodes in P3HT/PCBM organic solar cells.