Engineering Nanoscale Materials for Solar Cells
Date
2016
Authors
Osorio Mayon, Yahuitl
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Abstract
The purpose of this work is to contribute towards developing
high-efficiency low cost solar cells that have the potential to
decrease the cost of solar energy. The focus is on novel device
structures that aim to minimise losses and/or allow high
throughput fabrication for antimony sulphide (Sb2S3) and the
perovskite methyl ammonium lead iodide (MAPbI3).
The first part of the research is on planar Sb2S3 solar cells,
and led to a twofold efficiency increase through the use of a
planar Sb2S3 layer with a high proportion of c axis aligned
crystal planes perpendicular to the substrate. The transport of
photo generated carriers along the c-axis aligned Sb2S3 crystal
planes has a lower recombination rate and longer effective
diffusion lengths than for other crystal planes. A completely
planar top Sb2S3 surface on a textured (non planar) substrate was
fabricated from a non-planar sulphur rich Sb2S3 layer. The planar
top surface of the Sb2S3 layer facilitates the subsequent
deposition of compact, thin and uniform layers of other materials
which contributes to improve the photovoltaic performance.
The second part of the research focused on fabrication of porous
TiO2 layers via a flame aerosol system, applied to both Sb2S3 and
MAPbI3 solar cells. The flame aerosol system is a high throughput
deposition method that could rapidly coat a large area substrate
as part of a continuous industrial production line. The
mechanical stability of flame-made porous TiO2 layers is crucial
to withstanding the subsequent material depositions processes via
solution methods. Different annealing methods were used to
increase the mechanical stability of flame made porous layers for
solar cells. The porosity of the flame made porous TiO2 layers
was easily adjusted over a wide range: from 97% to 35%. A porous
TiO2 layer with a high porosity could improve the solar cell
efficiency by increasing the collection efficiency through better
infiltration of the other solar cell materials in the porous
layer. The optimised MAPbI3 solar cell with flame made porous
TiO2 layer had a comparable efficiency to the control MAPbI3
solar cell with the standard spin-coated porous TiO2 layer,
demonstrating its potential with scope for further improvement.
The efficiency and stability of perovskite solar cells could be
also improved by using SnO2 instead of TiO2 as the former has
better electronic and photo catalytic properties than the latter.
For this reason, MAPbI3 perovskite solar cells with a flame-made
porous SnO2 layer were also investigated. The MAPbI3 solar cell
with a flame-made porous SnO2 had promising efficiencies even
though the main limitation for a higher efficiency was the use of
a compact TiO2 layer with the porous SnO2 layer.
The work contained in this thesis provides pathways to reduce
recombination losses and fabricate a high-throughput low-cost
porous structure for Sb2S3 and MAPbI3 solar cells. The findings
from this work could also be implemented with other materials;
particularly with mixed-perovskites and sulphur based materials.
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solar cells, antimony tri-sulphide, titanium oxide, tin oxide, methyl ammonium lead iodide, flame spray aerosol, porous layers
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Thesis (PhD)
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