Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014)
    Energy Harvesting & Storage Tuesday Sessions
       Session EH-TuP

Paper EH-TuP10
Inorganic-organic Core-Shell Nanowire Solar Cells with Excellent Light-Trapping Properties

Tuesday, December 9, 2014, 4:00 pm, Room Mauka

Session: Energy Harvesting & Storage Poster Session
Presenter: Keisuke Sato, Tokyo Denki University, Japan
Authors: K. Sato, Tokyo Denki University, Japan
M. Dutta, National Institute for Materials Science, Japan
N. Fukata, National Institute for Materials Science, Japan
Correspondent: Click to Email
Development of solar cells using one-dimensional architecture, such as semiconductor nanowires (NWs), have been proceeding rapidly in recent years. The main advantage of such NWs-based solar cells is that they cause greater light absorption (minimal reflectivity) due to incident light-trapping within the NW arrays. This phenomenon is most glaringly apparent in silicon nanowires (SiNWs)-based solar cells, leading to higher absorbance per unit thickness than achieved by commercial crystalline Si solar cells. Thus, the introduction of the SiNW arrays with high light-trapping properties enable lower-cost cell production due to the massive reduction of the consumption of Si materials needed for cell fabrication. We have developed inorganic-organic core-shell NW solar cells in which the vertically-aligned SiNWs were surrounded by organic poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layer in order to further facilitate the cell fabrication. We report herein on the cell performances of Si-PEDOT:PSS core-shell NW solar cells with excellent light-trapping properties. To investigate the light-trapping capability, the lengths of the core-shell NWs were varied within the range from 2 to 8 μm. In the core-shell NWs with shorter length of 2 μm, the reflectance were suppressed to below 8%, which is extremely lower than the crystalline Si with value of 31%, over a wide spectrum range between 300 and 1000 nm. This suppression is far more effective for longer NW length, resulting in a reflectance of below 4.6% for the core-shell NWs with longer length of 8 μm. These results demonstrate that the longer core-shell NW arrays can extend the broadband anti-reflection effect due to enhanced light-trapping in NW arrays. However, the cell performances of such core-shell NW solar cells closely were intimately related to the NW length-dependent carrier transport efficiency rather than the light-trapping effects. The core-shell NW solar cells with shorter length of 2 μm exhibited the best cell performance with a power conversion efficiency (PCE) of approximately 7%, exceeding those with longer length of 8 μm (PCE of 3.7%). The depression of cell performance with the increase in the NW length was caused by inefficient carrier collection at electrodes due to the enhancement of the carrier recombination, because the transportation distances to electrodes were increased with NW length. Therefore, we suggest that it is important to simultaneously tune the NW length and light-trapping properties to be able to fabricate efficient inorganic-organic core-shell NW solar cells.