We use ultrasonic spray-coating to fabricate caesium containing triple-cation perovskite solar cells having a power conversion efficiency up to 17.8%. Our fabrication route involves a brief exposure of the partially wet spray-cast films to a coarse-vacuum; a process that is used to control film crystallisation. We show that films that are not vacuum exposed are relatively rough and inhomogeneous, while vacuum exposed films are smooth and consist of small and densely-packed perovskite crystals. The process techniques developed here represent a step towards a scalable and industrially compatible manufacturing process capable of creating stable and high-performance perovskite solar cells.
Memristors are one of the emerging technologies that can potentially replace state-of-the-art integrated electronic devices for advanced computing and digital and analog circuit applications including neuromorphic networks. Over the past few years, research and development mostly focused on revolutionizing the metal oxide materials, which are used as core components of the popular metal-insulator-metal memristors owing to their highly recognized resistive switching behavior. This paper outlines the recent advancements and characteristics of such memristive devices, with a special focus on (i) their established resistive switching mechanisms and (ii) the key challenges associated with their fabrication processes including the impeding criteria of material adaptation for the electrode, capping, and insulator component layers. Potential applications and an outlook into future development of metal oxide memristive devices are also outlined.
An encapsulation system comprising of a UV‐curable epoxy, a solution processed polymer interlayer, and a glass cover‐slip, is used to increase the stability of methylammonium lead triiodide (CH3NH3PbI3) perovskite planar inverted architecture photovoltaic (PV) devices. It is found this encapsulation system acts as an efficient barrier to extrinsic degradation processes (ingress of moisture and oxygen), and that the polymer acts as a barrier that protects the PV device from the epoxy before it is fully cured. This results in devices that maintain 80% of their initial power conversion efficiency after 1000 h of AM1.5 irradiation. Such devices are used as a benchmark and are compared with devices having initially enhanced efficiency as a result of a solvent annealing process. It is found that such solvent‐annealed devices undergo enhanced burn‐in and have a reduced long‐term efficiency, a result demonstrating that initially enhanced device efficiency does not necessarily result in long‐term stability.
Understanding nanoscale molecular order within organic electronic materials is a crucial factor in building better organic electronic devices. At present, techniques capable of imaging molecular order within a polymer are limited in resolution, accuracy, and accessibility. In this work, presented are secondary electron (SE) spectroscopy and secondary electron hyperspectral imaging, which make an exciting alternative approach to probing molecular ordering in poly(3‐hexylthiophene) (P3HT) with scanning electron microscope‐enabled resolution. It is demonstrated that the crystalline content of a P3HT film is reflected by its SE energy spectrum, both empirically and through correlation with nano‐Fourier‐transform infrared spectroscopy, an innovative technique for exploring nanoscale chemistry. The origin of SE spectral features is investigated using both experimental and modeling approaches, and it is found that the different electronic properties of amorphous and crystalline P3HT result in SE emission with different energy distributions. This effect is exploited by acquiring hyperspectral SE images of different P3HT films to explore localized molecular orientation. Machine learning techniques are used to accurately identify and map the crystalline content of the film, demonstrating the power of an exciting characterization technique.
Electrolytic
dissociation of lithium hexafluorophosphate (LiPF6) in
the nonaqueous cyclic propylene carbonate (PC) has been
investigated in the wide range of concentration (0.05–3.5 M)
by 7Li solution-state nuclear magnetic resonance (NMR)
spectroscopy. Two-dimensional heteronuclear Overhauser enhancement
spectroscopy NMR experiments have not only enabled the cation solvation
and ion-pairing to be directly monitored but additionally evidence
anion–solvent interaction at higher concentrations (>1.2
M)
of the PC electrolyte. Preliminary analysis of kinetic nOe data has
been made to determine site-dependent cross-relaxation rates for the
spatial interaction of the solvent with the Li+ cation
and the PF6
– anion. The concentration
dependence of the 7Li NMR self-diffusion coefficient (D
self), determined using very strong pulsed magnetic
field gradients (∼1700 Gauss/cm), depicts two breaks to mark
the solvation and ion-pairing events in a distinct manner. This in
turn has aided the determination of solvent coordination number and
average sizes of solvated and ion-paired clusters. Our results indicate
that in the contact ion pair (CIP)-dominated electrolyte (>2 M),
lithium-ion
mobility across the solvated and ion-paired environments appears to
be inhibited which makes the spectral distinction of solvated and
ion-paired environments possible. The concentration dependence of
the 7Li NMR spectral and diffusometry data is in striking
correspondence with that of bulk conductivity measurements and point
to the detrimental effect of CIP aggregates in impeding the ionic
conductivity at high salt concentrations. These results have significance
in understanding the structure and dynamics of lithium-ion solvates
that are ubiquitous in the working environment of a lithium-ion battery.
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