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The aim of this thesis was the development of materials and
device architectures for the preparation of efficient vacuum
deposited perovskite solar cells. The effect of different charge
transport layers, interfacial materials and electrodes on the
performance of perovskite solar cells was studied. Emphasis was
placed on the importance of reducing non-radiative
recombination within the perovskite and at the interfaces, which
is the key to maintain high photovoltage in a solar cell.
a novel approach to prepare mixed iodide-chloride
perovskites, using three-source vacuum deposition technique,
was presented. MAPbI3-xClx perovskite films showed a
homogenous morphology and good crystallinity, and were hence
used to fabricate thin-film diodes to examine the optoelectronic
properties. Under illumination, the photovoltage was found to be
larger as compared to pure iodide perovskite, reaching 1.13 V
and a power conversion efficiency exceeding 16%. In forward
bias, we detected intense electroluminescence with a quantum
yield of 0.3%, similar to that of state-of-the-art evaporated
MAPbI3 solar cells. The high quantum yield for
electroluminescence together with the long photoluminescence
lifetime suggests a reduction of the non-radiative recombination
rate.
The importance of the choice of suitable interfacial charge
transport layers, electrodes, and their combinations, was
highlighted in chapter 4. The MAPbI3 perovskite layer was
deposited by dual source vacuum deposition. BCP, Liq and their
combination were used as interlayers between the electron
transport layer and the top electrode. We observed that BCP and
Liq can lead to devices with high rectification, fill factor, and photovoltage. We also observed that the use of low work
function metals, such as Ba, can be beneficial for the reduction of
non-radiative recombination, although at the price of the device
stability.
In chapter 5, the optimization of the front contact in perovskite
solar cells was investigated. As in chapter 4, the MAPbI3
perovskite film was deposited by dual source vacuum deposition.
The hole transport layer which was used to fabricate the
perovskite solar cells is TaTm. To ensure an ohmic contact
between the TaTm layer and the ITO, an additional MoO3 layer
was placed in between the two materials. The hole extraction
properties of the MoO3/TaTm was evaluated by selectively
annealing either MoO3 (prior to the deposition of TaTm) or the
bilayer MoO3/TaTm (without pre-treatment on the MoO3), at
temperature ranging from 60 °C to 200 °C. We observed that
having TaTm deposited and annealed together with the MoO3
layer led to large improvement in fill factor (80%) and power
conversion efficiency (> 18%) at any annealing temperature, with
the best results obtained at 140 °C.
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