Understanding the open-circuit voltage in small molecule heterojunction photovoltaic devices
Chauhan, Virendra (2010) Understanding the open-circuit voltage in small molecule heterojunction photovoltaic devices. PhD thesis, University of Warwick.Full text not available from this repository.
Official URL: http://webcat.warwick.ac.uk/record=b2482490~S15
Organic photovoltaic devices continue to attract attention as they offer the prospect of
low-cost energy production on flexible substrates. However, there remains a need to
understand factors which affect device performance at a more fundamental level. One
particular area of focus has been related to the device open-circuit voltage (Voc) whose origins
are still the subject of debate. This thesis therefore sets out to try and understand and correlate
the electronic properties of materials with critical device parameters, such as the Voc.
The experimental determination of the work function, ionisation potential and electron
affinities are important for predicting and understanding the energetics at the interface formed
when two solids are combined. The offsets at the interface between different oxide /
phthalocyanine / fullerene heterojunctions were characterised. It was found that the upper
limit to Voc is governed by the offsets between the HOMO state in the donor and the LUMO
state of the acceptor (the effective bandgap). Furthermore, by understanding the electronic
structure and characterising device performance in the limit of low temperature, it was found
that the experimental Voc is limited by the reverse saturation current and the exciton binding
energy - a bottleneck for organic semiconductors.
An understanding of the benefits of incorporating molybdenum oxide into a device
architecture was achieved by conducting a thorough investigation on its electronic structure.
The conduction mechanism is believed to be dictated by a distribution of near Fermi level
defect states caused by non-stoichiometry. Finally, the effects of tuning the molecular
orientation on the device performance were investigated with a flat lying perylene derivative.
Optimised device architectures based on the photoactive ClAlPc / C60 heterojunction
displayed an efficiency of 3.0 %.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||Q Science > QD Chemistry
T Technology > TK Electrical engineering. Electronics Nuclear engineering
|Library of Congress Subject Headings (LCSH):||Organic electronics, Photovoltaic cells, Oxides -- Electric properties, Phthalocyanines -- Electric properties, Fullerenes -- Electric properties|
|Official Date:||August 2010|
|Institution:||University of Warwick|
|Theses Department:||Department of Chemistry|
|Supervisor(s)/Advisor:||Jones, Tim S.|
|Sponsors:||Engineering and Physical Sciences Research Council (EPSRC) ; Excitonic Solar Cell Supergen Consortium|
|Extent:||viii, 147 leaves : ill., charts|
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