Organic solar cells (OSCs) have shown great promise in becoming the next
generation of renewable energy due to its low cost, simple manufacturing process and
flexibility. A method of efficiency improvement in OSCs is by incorporating metallic
nanoparticles (NPs). While various reports have reported that incorporation of NPs
improve OSC efficiencies due to the Localized Surface Plasmon Resonance (LSPR)
effect, the investigations have lacked depth and a detailed investigation is necessary to
fully understand the device mechanisms of these OSCs.
In this thesis, we first investigate OSCs incorporating Au NPs into the hole
collection Poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)
layer. Our theoretical and experimental results show that the very strong near field
around Au NPs due to LSPR mainly distributes laterally along the PEDOT:PSS rather
than vertically into the adjacent active layer, leading to minimal enhancement of light
absorption in the active layer. With optical effects proven to be minor contributors to
device performance improvements, we investigate the electrical properties of the
OSCs and obtain insights into the detailed device mechanisms. Improvements in
power conversion efficiency (PCE) of solar cells are found to originate from the
enlarged active layer/PEDOT:PSS interfacial area and improved PEDOT:PSS
conductivity. At high NP concentrations, reduced exciton quenching at donor/acceptor
junctions is found to cause PCE deterioration.
Next, the effects of Au NPs incorporated into the active layer of OSCs with a
newly synthesized donor polymer are investigated in detail. Our experimental and
theoretical results both show that LSPR introduced by the NPs can enhance the light
absorption in the active layer of OSCs because the strong LSPR near field mainly
distributes laterally along the active layer. Combined with our previous study, our
results strongly suggest that NPs have to be incorporated in the active layer in order to
harvest light by the LSPR effect. Meanwhile, our results show that the electrical
properties of NPs improve at low concentration of NPs. When NP concentration is
increased, the electrical properties deteriorates and counter-diminish the optical
enhancement from LSPR and reduces the overall performance improvement.
Finally, we demonstrate efficiency improvement in OSCs by ~22% through
incorporating Au NPs into all polymer layers. Au NPs are found to have distinct
mechanisms in improving device performance when incorporated in different polymer
layers. Our results indicate that the efficiency improvement is the accumulated effects
of incorporating NPs in the individual layers and that coupling is not observed in this
device configuration.
On the whole, our findings highlight the importance that both optical and
electrical properties need to be studied and optimized simultaneously for achieving
enhancement in PCE of OSCs. We have carried out a detailed study on incorporating
NP in various layers and our results are highly useful for the design of high efficiency
OSCs incorporating metallic NPs. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/174537 |
| Date | January 2011 |
| Creators | Fung, Dat-shun, Dixon., 馮達信. |
| Contributors | Choy, WCH |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B47849794 |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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