Plasmon enhancement of organic photovoltaic efficiency in bulk-heterojunction cells of P3HT/PCBM

• Main Author: Lau, Vincent Koon Tuck.
• Other Authors: Subodh Gautam Mhaisalkar
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Materials::Organic/Polymer electronics; DRNTU::Engineering::Materials::Energy materials; DRNTU::Engineering::Materials::Photonics and optoelectronics materials
• Online Access: http://hdl.handle.net/10356/15306
• Institution: Nanyang Technological University

An organic photovoltaic (OPV) cell was shown to have increased power conversion efficiency (PCE) due to an enhancement of optical absorption via the coupling of photon with the surface plasmon resonance (SPR) in spherical Au nanoparticles deposited on the photo-anode. Work was also done to show the correlation of Au nanoparticles size with the amount of PCE enhancement observed. Our fabricated devices were based on bulk-heterojunction OPV cell architecture, with a blend of poly(3-hexylthiophene (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) as the active layer, and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) as the charge transfer layer that reduces the difference in work function of the indium tin oxide (ITO) anode with the active layer. We first used 100nm Au Si-core nanoshells in two different cells – one with the nanoshells blended with the active layer and the other drop-casted onto the ITO surface. With these two cells, we showed the importance of particle size compatibility with the active layer thickness. Subsequently, we moved on to use 9nm and 48nm spherical Au nanoparticles. Through the use of citrate molecules as surfactants, we developed a novel method of deposition by immersing plasma-cleaned ITO substrates into an Au colloid to adhere 9-48nm Au nanoparticles onto the ITO surface without the need for any binding agents. From our experimental results in comparison to pristine cells, we found the optimal immersion time to be 1.5hrs and 1hr for the best improvement of up to 105.8% and 43.5% increment in PCE for 9nm and 48nm Au nanoparticles respectively. Next we explained the effects of non-optimal immersion times on PCE, through the use of secondary electron images (SEI) of the Au-seeded ITO surface. Finally, with the help of UV-Vis spectrometry and incident photon to charge carrier efficiency (IPCE) measurements, we showed that SPR can be applied to enhance the optical absorption of the active layer.