Combustion Synthesized Zinc Oxide Electron‐Transport Layers for Efficient and Stable Perovskite Solar Cells

Perovskite solar cells (PSCs) have advanced rapidly with power conversion efficiencies (PCEs) now exceeding 22%. Due to the long diffusion lengths of charge carriers in the photoactive layer, a PSC device architecture comprising an electron‐ transporting layer (ETL) is essential to optimize charge flow and collection for maximum performance. Here, a novel approach is reported to low temperature, solution‐processed ZnO ETLs for PSCs using combustion synthesis. Due to the intrinsic passivation effects, high crystallinity, matched energy levels, ideal surface topography, and good chemical compatibility with the perovskite layer, this combustion‐derived ZnO enables PCEs approaching 17–20% for three types of perovskite materials systems with no need for ETL doping or surface functionalization.     

Benzodithiophene Hole‐Transporting Materials for Efficient Tin‐Based Perovskite Solar Cells

Developing efficient interfacial hole transporting materials (HTMs) is crucial for achieving high‐performance Pb‐free Sn‐based halide perovskite solar cells (PSCs). Here, a new series of benzodithiophene (BDT)‐based organic small molecules containing tetra‐ and di‐triphenyl amine donors prepared via a straightforward and scalable synthetic route is reported. The thermal, optical, and electrochemical properties of two BDT‐based molecules are shown to be structurally and energetically suitable to serve as HTMs for Sn‐based PSCs. It is reported here that ethylenediammonium/formamidinium tin iodide solar cells using BDT‐based HTMs deliver a champion power conversion efficiency up to 7.59%, outperforming analogous reference solar cells using traditional and expensive HTMs. Thus, these BDT‐based molecules are promising candidates as HTMs for the fabrication of high‐performance Sn‐based PSCs.     

Hole‐Transfer Dependence on Blend Morphology and Energy Level Alignment in Polymer: ITIC Photovoltaic Materials

Bulk‐heterojunction organic photovoltaic materials containing nonfullerene acceptors (NFAs) have seen remarkable advances in the past year, finally surpassing fullerenes in performance. Indeed, acceptors based on indacenodithiophene (IDT) have become synonymous with high power conversion efficiencies (PCEs). Nevertheless, NFAs have yet to achieve fill factors (FFs) comparable to those of the highest‐performing fullerene‐based materials. To address this seeming anomaly, this study examines a high efficiency IDT‐based acceptor, ITIC , paired with three donor polymers known to achieve high FFs with fullerenes, PTPD3T , PBTI3T , and PBTSA3T . Excellent PCEs up to 8.43% are achieved from PTPD3T:ITIC blends, reflecting good charge transport, optimal morphology, and efficient ITIC to PTPD3T hole‐transfer, as observed by femtosecond transient absorption spectroscopy. Hole‐transfer is observed from ITIC to PBTI3T and PBTSA3T , but less efficiently, reflecting measurably inferior morphology and nonoptimal energy level alignment, resulting in PCEs of 5.34% and 4.65%, respectively. This work demonstrates the importance of proper morphology and kinetics of ITIC → donor polymer hole‐transfer in boosting the performance of polymer: ITIC photovoltaic bulk heterojunction blends.     

Polymer Doping Enables a Two‐Dimensional Electron Gas for High‐Performance Homojunction Oxide Thin‐Film Transistors

High‐performance solution‐processed metal oxide (MO) thin‐film transistors (TFTs) are realized by fabricating a homojunction of indium oxide (In₂O₃) and polyethylenimine (PEI)‐doped In₂O₃ (In₂O₃:x% PEI, x = 0.5–4.0 wt%) as the channel layer. A two‐dimensional electron gas (2DEG) is thereby achieved by creating a band offset between the In₂O₃ and PEI‐In₂O₃ via work function tuning of the In₂O₃:x% PEI, from 4.00 to 3.62 eV as the PEI content is increased from 0.0 (pristine In₂O₃) to 4.0 wt%, respectively. The resulting devices achieve electron mobilities greater than 10 cm² V^?1 s^?1 on a 300 nm SiO₂ gate dielectric. Importantly, these metrics exceed those of the devices composed of the pristine In₂O₃ materials, which achieve a maximum mobility of ≈4 cm² V^?1 s^?1. Furthermore, a mobility as high as 30 cm² V^?1 s^?1 is achieved on a high‐k ZrO₂ dielectric in the homojunction devices. This is the first demonstration of 2DEG‐based homojunction oxide TFTs via band offset achieved by simple polymer doping of the same MO material.     

Carbon Free and Noble Metal Free Ni2Mo6S8 Electrocatalyst for Selective Electrosynthesis of H2O2

Electrocatalytic two-electron reduction of oxygen is a promising method for producing sustainable H₂O₂ but lacks low-cost and selective electrocatalysts. Here, the Chevrel phase chalcogenide Ni₂Mo₆S₈ is presented as a novel active motif for reducing oxygen to H₂O₂ in an aqueous electrolyte. Although it has a low surface area, the Ni₂Mo₆S₈ catalyst exhibits exceptional activity for H₂O₂ synthesis with >90% H₂O₂ molar selectivity across a wide potential range. Chemical titration verified successful generation of H₂O₂ and confirmed rates as high as 90 mmol H₂O₂ g_cat⁻¹ h⁻¹. The outstanding activities are attributed to the ligand and ensemble effects of Ni that promote H₂O dissociation and proton-coupled reduction of O₂ to HOO*, and the spatial effect of the Chevrel phase structure that isolates Ni active sites to inhibit O O cleavage. The synergy of these effects delivers fast and selective production of H₂O₂ with high turn-over frequencies of ≈30 s⁻¹. In addition, the Ni₂Mo₆S₈ catalyst has a stable crystal structure that is resistive for oxidation and delivers good catalyst stability for continuous H₂O₂ production. The described Ni-Mo₆S₈ active motif can unlock new opportunities for designing Earth-abundant electrocatalysts to tune oxygen reduction for practical H₂O₂ production.     

Optimized conditions for imaging the effects of bonding charge density in electron microscopy

We report on the observability of valence bonding effects in aberration-corrected high resolution electron microscopy (HREM) images along the [0 1 0] projection of the mineral Forsterite (Mg₂SiO₄). We have also performed exit wave restorations using simulated noisy images and have determined that both the intensities of individual images and the modulus of the restored complex exit wave are most sensitive to bonding effects at a level of 25% for moderately thick samples of 20-25 nm. This relatively large thickness is due to dynamical amplification of bonding contrast arising from partial de-channeling of 1s states. Simulations also suggest that bonding contrast is similarly high for an un-corrected conventional electron microscope, implying an experimental limitation of signal to noise ratio rather than spatial resolution.     

Charge defects glowing in the dark

We investigate the effects of local charge defects in HREM imaging, using electron densities calculated by density functional methods. As a model of a planar interface with a local charge defect we use the polar MgO square root (111)-3 x 3R30 degrees surface, which has an additional hole per surface unit cell. A complimentary example, the non-polar MgO (100) surface that has no local charge defect is simulated for comparison. We show that the contrast due to local charge defects is rather high, and suggest that they should be directly observable.     

Gas-phase mercury in the atmosphere over the southern Baltic Sea coast

Results of atmospheric total gaseous mercury (TGM) measurements performed at two Baltic Sea coastal stations, Peninsula Hel (Poland) and Preila (Lithuania), from June 16 to August 11, 1997, are presented. High time-resolution data were obtained by using automated atomic absorption mercury vapor analyzers (Model Gardis-1A). Analysis of TGM concentration data (directional distribution, correlation with meteorological parameters, diurnal variability) detected the Baltic sea, in particular its southern part and Gulf of Gdansk, as the main gaseous mercury source for the region during the summer months. The source seemed to be activated by solar radiation, air temperature, and, probably, wind.     

Group refractive index reconstruction with broadband interferometric confocal microscopy

We propose a novel method of measuring the group refractive index of biological tissues at the micrometer scale. The technique utilizes a broadband confocal microscope embedded into a Mach-Zehnder interferometer, with which spectral interferograms are measured as the sample is translated through the focus of the beam. The method does not require phase unwrapping and is insensitive to vibrations in the sample and reference arms. High measurement stability is achieved because a single spectral interferogram contains all the information necessary to compute the optical path delay of the beam transmitted through the sample. Included are a physical framework defining the forward problem, linear solutions to the inverse problem, and simulated images of biologically relevant phantoms.     

Inverse scattering for frequency-scanned full-field optical coherence tomography

Full-field optical coherence tomography (OCT) is able to image an entire en face plane of scatterers simultaneously, but typically the focus is scanned through the volume to acquire three-dimensional structure. By solving the inverse scattering problem for full-field OCT, we show it is possible to computationally reconstruct a three-dimensional volume while the focus is fixed at one plane inside the sample. While a low-numerical-aperture (NA) OCT system can tolerate defocus because the depth of field is large, for high NA it is critical to correct for defocus. By deriving a solution to the inverse scattering problem for full-field OCT, we propose and simulate an algorithm that recovers object structure both inside and outside the depth of field, so that even for high NA the focus can be fixed at a particular plane within the sample without compromising resolution away from the focal plane.