Miocene Fossils Reveal Ancient Roots for New Zealand’s Endemic Mystacina (Chiroptera) and Its Rainforest Habitat

This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.The New Zealand endemic bat family Mystacinidae comprises just two Recent species referred to a single genus, Mystacina. The family was once more diverse and widespread, with an additional six extinct taxa recorded from Australia and New Zealand. Here, a new mystacinid is described from the early Miocene (19–16 Ma) St Bathans Fauna of Central Otago, South Island, New Zealand. It is the first pre-Pleistocene record of the modern genus and it extends the evolutionary history of Mystacina back at least 16 million years. Extant Mystacina species occupy old-growth rainforest and are semi-terrestrial with an exceptionally broad omnivorous diet. The majority of the plants inhabited, pollinated, dispersed or eaten by modern Mystacina were well-established in southern New Zealand in the early Miocene, based on the fossil record from sites at or near where the bat fossils are found. Similarly, many of the arthropod prey of living Mystacina are recorded as fossils in the same area. Although none of the Miocene plant and arthropod species is extant, most are closely related to modern taxa, demonstrating potentially long-standing ecological associations with Mystacina

Multimodal Microscale Imaging of Textured Perovskite-Silicon Tandem Solar Cells.

Halide perovskite/crystalline silicon (c-Si) tandem solar cells promise power conversion efficiencies beyond the limits of single-junction cells. However, the local light-matter interactions of the perovskite material embedded in this pyramidal multijunction configuration, and the effect on device performance, are not well understood. Here, we characterize the microscale optoelectronic properties of the perovskite semiconductor deposited on different c-Si texturing schemes. We find a strong spatial and spectral dependence of the photoluminescence (PL) on the geometrical surface constructs, which dominates the underlying grain-to-grain PL variation found in halide perovskite films. The PL response is dependent upon the texturing design, with larger pyramids inducing distinct PL spectra for valleys and pyramids, an effect which is mitigated with small pyramids. Further, optimized quasi-Fermi level splittings and PL quantum efficiencies occur when the c-Si large pyramids have had a secondary smoothing etch. Our results suggest that a holistic optimization of the texturing is required to maximize light in- and out-coupling of both absorber layers and there is a fine balance between the optimal geometrical configuration and optoelectronic performance that will guide future device designs

Using pulsed mode scanning electron microscopy for cathodoluminescence studies on hybrid perovskite films

Abstract: The use of pulsed mode scanning electron microscopy cathodoluminescence (CL) for both hyperspectral mapping and time-resolved measurements is found to be useful for the study of hybrid perovskite films, a class of ionic semiconductors that have been shown to be beam sensitive. A range of acquisition parameters is analysed, including beam current and beam mode (either continuous or pulsed operation), and their effect on the CL emission is discussed. Under optimized acquisition conditions, using a pulsed electron beam, the heterogeneity of the emission properties of hybrid perovskite films can be resolved via the acquisition of CL hyperspectral maps. These optimized parameters also enable the acquisition of time-resolved CL of polycrystalline films, showing significantly shorter lived charge carriers dynamics compared to the photoluminescence analogue, hinting at additional electron beam-specimen interactions to be further investigated. This work represents a promising step to investigate hybrid perovskite semiconductors at the nanoscale with CL

Optical emission from focused ion beam milled halide perovskite device cross‐sections

Funder: Jardine Foundation and Cambridge TrustFunder: Cambridge RoyceFunder: Dr. Christian Monachon from AttolightAbstract: Cross‐sectional transmission electron microscopy has been widely used to investigate organic–inorganic hybrid halide perovskite‐based optoelectronic devices. Electron‐transparent specimens (lamellae) used in such studies are often prepared using focused ion beam (FIB) milling. However, the gallium ions used in FIB milling may severely degrade the structure and composition of halide perovskites in the lamellae, potentially invalidating studies performed on them. In this work, the close relationship between perovskite structure and luminescence is exploited to examine the structural quality of perovskite solar cell lamellae prepared by FIB milling. Through hyperspectral cathodoluminescence (CL) mapping, the perovskite layer was found to remain optically active with a slightly blue‐shifted luminescence. This finding indicates that the perovskite structure is largely preserved upon the lamella fabrication process although some surface amorphisation occurred. Further changes in CL due to electron beam irradiation were also recorded, confirming that electron dose management is essential in electron microscopy studies of carefully prepared halide perovskite‐based device lamellae

A Highly Emissive Surface Layer in Mixed-Halide Multication Perovskites.

Mixed-halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution-processed triple-cation mixed-halide (Cs0.06 MA0.15 FA0.79 )Pb(Br0.4 I0.6 )3 perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar-equivalent illumination. It is found that the illumination leads to localized surface sites of iodide-rich perovskite intermixed with passivating PbI2 material. Time- and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide-rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed-halide mixed-cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures

Stabilized tilted-octahedra halide perovskites inhibit local formation of performance-limiting phases.

Efforts to stabilize photoactive formamidinium (FA)–based halide perovskites for perovskite photovoltaics have focused on the growth of cubic formamidinium lead iodide (α-FAPbI3) phases by empirically alloying with cesium, methylammonium (MA) cations, or both. We show that such stabilized FA-rich perovskites are noncubic and exhibit ~2° octahedral tilting at room temperature. This tilting, resolvable only with the use of local nanostructure characterization techniques, imparts phase stability by frustrating transitions from photoactive to hexagonal phases. Although the bulk phase appears stable when examined macroscopically, heterogeneous cation distributions allow microscopically unstable regions to form; we found that these transitioned to hexagonal polytypes, leading to local trap-assisted performance losses and photoinstabilities. Using surface-bound ethylenediaminetetraacetic acid, we engineered an octahedral tilt into pure α-FAPbI3 thin films without any cation alloying. The templated photoactive FAPbI3 film was extremely stable against thermal, environmental, and light stressors

Proton Radiation Hardness of Perovskite Tandem Photovoltaics.

Monolithic [Cs0.05(MA0. 17FA0. 83)0.95]Pb(I0.83Br0.17)3/Cu(In,Ga)Se2 (perovskite/CIGS) tandem solar cells promise high performance and can be processed on flexible substrates, enabling cost-efficient and ultra-lightweight space photovoltaics with power-to-weight and power-to-cost ratios surpassing those of state-of-the-art III-V semiconductor-based multijunctions. However, to become a viable space technology, the full tandem stack must withstand the harsh radiation environments in space. Here, we design tailored operando and ex situ measurements to show that perovskite/CIGS cells retain over 85% of their initial efficiency even after 68 MeV proton irradiation at a dose of 2 × 1012 p+/cm2. We use photoluminescence microscopy to show that the local quasi-Fermi-level splitting of the perovskite top cell is unaffected. We identify that the efficiency losses arise primarily from increased recombination in the CIGS bottom cell and the nickel-oxide-based recombination contact. These results are corroborated by measurements of monolithic perovskite/silicon-heterojunction cells, which severely degrade to 1% of their initial efficiency due to radiation-induced recombination centers in silicon.F.L. acknowledges financial support from the Alexander von Humboldt Foundation via the Feodor Lynen program and thanks Prof. Sir R. Friend for supporting his Fellowship at the Cavendish Laboratory. This work was supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (HYPERION, grant agreement number 756962). M.J, A.A.A., E.K., and S.A. acknowledge financial support from the German Federal Ministry of Education and Research (BMBF) via program “Materialforschung für die Energiewende” (grant no. 03SF0540), by the German Federal Ministry for Economic Affairs and Energy (BMWi) through the ‘PersiST’ project (Grant No. 0324037C). T.B. C.A.K. and R.S. acknowledge funding by BMWi through the speedCIGS (grant no. 0324095E) and EFFCIS project (grant no. 0324076D). D.K. and M.C. acknowledge financial support from the Dutch Ministry of Economic Affairs, via The Top-consortia Knowledge and Innovation (TKI) Program ‘‘Photovoltaic modules based on a p-i-n stack, manufactured on a roll-to-roll line featuring high efficiency, stability and strong market perspective’’ (PVPRESS) (TEUE118010) and “Bridging the voltage gap” (BRIGHT) (1721101). K. F. acknowledges the George and Lilian Schiff Fund, the Engineering and Physical Sciences Research Council (EPSRC), the Winton Sustainability Fellowship, and the Cambridge Trust for funding. S.D.S. acknowledges the Royal Society and Tata Group (UF150033). The authors acknowledge the EPSRC for funding (EP/R023980/1). This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 841265. A.R.B. acknowledges funding from a Winton Studentship, Oppenheimer Studentship, and funding from the Engineering and Physical Sciences Research Council (EPSRC) Doctoral Training Centre in Photovoltaics (CDT-PV). K.G. acknowledges the Polish Ministry of Science and Higher Education within the Mobilnosc Plus program (Grant No. 1603/MOB/V/2017/0)

Performance-limiting nanoscale trap clusters at grain junctions in halide perovskites.

Halide perovskite materials have promising performance characteristics for low-cost optoelectronic applications. Photovoltaic devices fabricated from perovskite absorbers have reached power conversion efficiencies above 25 per cent in single-junction devices and 28 per cent in tandem devices1,2. This strong performance (albeit below the practical limits of about 30 per cent and 35 per cent, respectively3) is surprising in thin films processed from solution at low-temperature, a method that generally produces abundant crystalline defects4. Although point defects often induce only shallow electronic states in the perovskite bandgap that do not affect performance5, perovskite devices still have many states deep within the bandgap that trap charge carriers and cause them to recombine non-radiatively. These deep trap states thus induce local variations in photoluminescence and limit the device performance6. The origin and distribution of these trap states are unknown, but they have been associated with light-induced halide segregation in mixed-halide perovskite compositions7 and with local strain8, both of which make devices less stable9. Here we use photoemission electron microscopy to image the trap distribution in state-of-the-art halide perovskite films. Instead of a relatively uniform distribution within regions of poor photoluminescence efficiency, we observe discrete, nanoscale trap clusters. By correlating microscopy measurements with scanning electron analytical techniques, we find that these trap clusters appear at the interfaces between crystallographically and compositionally distinct entities. Finally, by generating time-resolved photoemission sequences of the photo-excited carrier trapping process10,11, we reveal a hole-trapping character with the kinetics limited by diffusion of holes to the local trap clusters. Our approach shows that managing structure and composition on the nanoscale will be essential for optimal performance of halide perovskite devices

Proton‐Radiation Tolerant All‐Perovskite Multijunction Solar Cells

Funder: European Research Council; Id: http://dx.doi.org/10.13039/501100000781Funder: Engineering and Physical Sciences Research Council; Id: http://dx.doi.org/10.13039/501100000266Funder: European Union's Horizon 2020Abstract: Radiation‐resistant but cost‐efficient, flexible, and ultralight solar sheets with high specific power (W g−1) are the “holy grail” of the new space revolution, powering private space exploration, low‐cost missions, and future habitats on Moon and Mars. Herein, this study investigates an all‐perovskite tandem photovoltaic (PV) technology that uses an ultrathin active layer (1.56 µm) but offers high power conversion efficiency, and discusses its potential for high‐specific‐power applications. This study demonstrates that all‐perovskite tandems possess a high tolerance to the harsh radiation environment in space. The tests under 68 MeV proton irradiation show negligible degradation (22%. Using high spatial resolution photoluminescence (PL) microscopy, it is revealed that defect clusters in GaAs are responsible for the degradation of current space‐PV. By contrast, negligible reduction in PL of the individual perovskite subcells even after the highest dose studied is observed. Studying the intensity‐dependent PL of bare low‐gap and high‐gap perovskite absorbers, it is shown that the VOC, fill factor, and efficiency potentials remain identically high after irradiation. Radiation damage of all‐perovskite tandems thus has a fundamentally different origin to traditional space PV