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In the last decade, perovskite semiconductors have triggered a revolution in solar cell research. However, critical issues remain concerning the stability of metal-halide perovskites, which need to be overcome to enable a large scale commercialisation of perovskite photovoltaics (PV). While the rather poor environmental stability of these perovskites is usually attributed to their ionic nature rendering them sensitive to moisture and oxygen, the actual contribution of mobile ions to the total degradation loss under different environmental conditions is poorly understood. In this work, we reveal that the initial degradation of perovskite semiconductors is largely the result of mobile ion-induced internal field screening - a phenomenon that has not been previously discussed in relation to the degradation of perovskite solar cells. The increased field screening leads to a decrease in the steady-state power conversion efficiency mainly due to a large reduction in current density, while the efficiency at high scan speeds (>1000 V/s) where the ions are immobilized is much less affected. We also show that interfacial recombination does not increase upon ageing, yet the open-circuit voltage (VOC) decreases as the result of an increase in the mobile ion density upon ageing. Furthermore, similar ionic losses appear under different external stressors, in particular when there are free charges present in the absorber layer. This work reveals a key degradation mechanism, providing new insights into initial device degradation before chemical or extrinsic mechanical device degradation effects manifest, and it highlights the critical role mobile ions play therein.

Ultra-narrow bandwidth single-photon sources operating at room temperature are of vital importance for viable optical quantum technologies at scale, including quantum key distribution, cloud-based quantum information processing networks, and quantum metrology. Here we show a room-temperature single-photon source generating polarised photons at a rate of 5MHz based on an inorganic CsPbI3 perovskite quantum dot embedded in a tunable open optical microcavity. When coupled to the mode of the optical cavity, the quantum dot room-temperature emission becomes single-mode and the spectrum narrows down to just ∼ 1 nm. The excellent directionality of the optical modes enables high single-mode collection at RT, offering promising performance for photonic and quantum technology applications. We measure 94% single-photon purity under pulsed and continuous-wave (CW) excitation.

Halogen mixing in lead-halide perovskites is an effective route for tuning the band gap in light emission and multijunction solar cell applications. Here we report the effect of halogen mixing on the optoelectronic properties of lead-halide perovskites from theory and experiment. We applied the virtual crystal approximation within density functional theory, the GW approximation, and the Bethe-Salpeter equation to calculate structural, vibrational, and optoelectronic properties for a series of mixed halide perovskites. We separately perform spectroscopic measurements of these properties and analyze the impact of halogen mixing on quasiparticle band gaps, effective masses, absorption coefficients, charge-carrier mobilities, and exciton binding energies. Our joint theoretical-experimental study demonstrates that iodide-bromide mixed-halide perovskites can be modeled as homovalent alloys, and local structural distortions do not play a significant role for the properties of these mixed species. Our study outlines a general theoretical-experimental framework for future investigations of novel chemically mixed systems.

Having captivated the research community with simple fabrication processes and staggering device efficiencies, perovskite-based optoelectronics are already on the way to commercialization. However, one potential obstacle to this commercialization is the almost exclusive use of toxic, highly coordinating, high boiling point solvents to make perovskite precursor inks. Herein, we demonstrate that nonpolar organic solvents, such as toluene, can be combined with butylamine to form an effective solvent for alkylammonium-based perovskites. Beyond providing broader solvent choice, our finding opens the possibility of blending perovskite inks with a wide range of previously incompatible materials, such as organic molecules, polymers, nanocrystals, and structure-directing agents. As a demonstration, using this solvent, we blend the perovskite ink with 6,6-phenyl-C-61-butyric acid methyl ester and show improved perovskite crystallization and device efficiencies. This processing route may enable a myriad of new possibilities for tuning the active layers in efficient photovoltaics, light-emitting diodes, and other semiconductor devices.

Despite fast development of hybrid perovskite solar cells, there are many fundamental questions related to the perovskite film which remain open. For example, there are contradicting theoretical reports on the role of the organic methylammonium cation (CH

We studied charge transport in anodized TiO2 nanotubes in the context of their application in dye-sensitized solar cells. Optical-pump-THz- probe spectroscopy revealed short free carrier lifetimes of about 15-30 ps, which we attribute to shallow trapping. © 2013 IEEE.

Novel materials for solar cells have been developing very rapidly, for example perovskite based solar cells have recently experienced an unprecedented increase in efficiency to values exceeding 20% within just two years. An important part of the performance of these cells are issues such as stability, cost and manufacturability. In this presentation we demonstrate that the hole transporting layer in such cells can be replaced with polymer-functionalized single-walled carbon nanotubes (SWNTs) embedded in an insulating polymer matrix. With such a composite structure a power conversion efficiency of up to 15.3% is achieved. This layer shows a much improved moisture resistance and at the same time has a thermal stability significantly superior to other hole-transporting materials employed in high-performance perovskite solar cells. This is likely to be a critical development for enhancing the long-term stability of high-efficiency perovskite solar cells. In addition the same type of SWNT/polymer hole transporting layer can be employed in both conventional organic PhotoVoltaic devices and devices made using colloidal quantum dots, both of which show efficiencies close to 10%. This type of novel hole transporting layer made from carbon nanotube may well have a very extensive range of applications based on its combination of selective conduction and robust performances

The commonly accepted significance of this sacrifice is well stated in BROWN, DRIVER and BRIGGS, Hebrew Lexicon, p. 257a: "the common and most ancient sacrifice whose essential rite was eating the flesh of the victim at a feast in which the god of the clan shared by receiving the blood and the fat pieces." This explanation arises out of totemistic theories of the origin of religion such as were put forward in Robertson SMITH'S The Religion of the Semites. I find myself far from happy about that theory, and it seems to be impossible that a high-god could ever develop from a low-god. In any case, totemistic origins of religion or not, the above quoted statement does rely on the theories of Robertson SMITH. This first paragraph of G. Buchanan GRAY'S Sacrifice in the Old Testament makes this plain. He quotes (p. 1) from Robertson SMITH: "The predominance assigned in ancient ritual to animal sacrifices corresponds to the predominance of the type of sacrifice which is not a mere payment of tribute, but an act of social fellowship between the deity and his worshippers." and "The leading idea in the animal sacrifices of the Semites.... was not that of a gift made over to the god, but of an act of communion, in which the god and his worshippers unite by partaking together of the flesh and blood of a sacred victim.'