The effect of metal sulfides on hole and electron transport buffer layers in organic photovoltaics: experimental and numerical device simulation investigations.
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Date
2022
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Abstract
Organic solar cells (OSCs) are promising alternative renewable energy sources
that often suffer from insufficient absorption of solar radiation, short exciton lifetimes
and small diffusion length of their charge carriers. Several strategies are being
investigated to overcome these challenges in a move towards the commercialization
of this solar cell technology. Increasing the path-length of incident electromagnetic
radiation within the photo-absorbing layer of the solar cell, may elongate the time
that light spends within the solar cell, thereby increasing the light-matter interaction
time and consequently the photo-absorption within the photo-active material
of the solar cell. The process described may be accomplished if suitable plasmonic
metal nano-structures are added into the solar cell matrix. This intervention may
also enhance the collection of the photo-generated charge carriers.
The effects of metal sulphide nanoparticles incorporation in organic solar cells
were studied and presented in this thesis. The metal sulphide nanoparticles were
characterized and introduced into the hole- and electron- transport layers of fullerene
and non-fullerene electron acceptors based solar cells, to elicit improved photoabsorption
via the localized surface plasmon effects and facilitate better charge
collection at the electrodes. Devices were fabricated both in an ambient environment
and in a controlled environment (Nitrogen filled glovebox). The metal sulphide
nanoparticles were incorporated in the fabricated solar devices using both the conventional
and inverted device architectures. The power conversion efficiencies of
the devices improved significantly after the incorporation of these nanoparticles.
Device numerical simulation studies were also performed to reproduce some of the
experimental results with a view to further investigating the devices and discussing
their charge transport characteristics. The simulation results show improved charge
carrier characteristics from the metal-sulphide doped devices by way of improved
conductivity and shifted Fermi level offsets which were aided by the presence of the
metal-sulphides.
Asides from successfully achieving improved device performances in the investigations
and simulations carried out in this thesis, this thesis successfully demonstrated
the incorporation of nano-composites in non-fullerene acceptors-based organic solar
cells for the first time to the best of our knowledge.
Description
Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.