Increasing Photostability of Inverted Nonfullerene Organic Solar Cells by using Fullerene Derivative Additives

Organic solar cells (OSCs) recently achieved efficiencies of over 18% and are well on their way to practical applications, but still considerable stability issues need to be overcome. One major problem emerges from the electron transport material zinc oxide (ZnO), which is mainly used in the inverted device architecture and decomposes many high-performance nonfullerene acceptors due to its photocatalytic activity. In this work, we add three different fullerene derivatives—PC71BM, ICMA, and BisPCBM—to an inverted binary PBDB-TF:IT-4F system in order to suppress the photocatalytic degradation of IT-4F on ZnO via the radical scavenging abilities of the fullerenes. We demonstrate that the addition of 5% fullerene not only increases the performance of the binary PBDB-TF:IT-4F system but also significantly improves the device lifetime under UV illumination in an inert atmosphere. While the binary devices lose 20% of their initial efficiency after only 3 h, this time is increased fivefold for the most promising ternary devices with ICMA. We attribute this improvement to a reduced photocatalytic decomposition of IT-4F in the ternary system, which results in a decreased recombination. We propose that the added fullerenes protect the IT-4F by acting as a sacrificial reagent, thereby suppressing the trap state formation. Furthermore, we show that the protective effect of the most promising fullerene ICMA is transferable to two other binary systems PBDB-TF:BTP-4F and PTB7-Th:IT-4F. Importantly, this effect can also increase the air stability of PBDB-TF:IT-4F. This work demonstrates that the addition of fullerene derivatives is a transferable and straightforward strategy to improve the stability of OSCs

Silver-Bismuth Based 2D Double Perovskites (4FPEA)(4)AgBiX8 (X = Cl, Br, I): Highly Oriented Thin Films with Large Domain Sizes and Ultrafast Charge-Carrier Localization

Two-dimensional (2D) hybrid double perovskites are a promising emerging class of materials featuring superior intrinsic and extrinsic stability over their 3D parent structures, while enabling additional structural diversity and tunability. Here, we expand the Ag-Bi-based double perovskite system, comparing structures obtained with the halides chloride, bromide, and iodide and the organic spacer cation 4-fluorophenethylammonium (4FPEA) to form the n = 1 Ruddlesden-Popper (RP) phases (4FPEA)(4)AgBiX8 (X = Cl, Br, I). We demonstrate access to the iodide RP-phase through a simple organic spacer, analyze the different properties as a result of halide substitution and incorporate the materials into photodetectors. Highly oriented thin films with very large domain sizes are fabricated and investigated with grazing incidence wide angle X-ray scattering, revealing a strong dependence of morphology on substrate choice and synthesis parameters. First-principles calculations confirm a direct band gap and show type Ib and IIb band alignment between organic and inorganic quantum wells. Optical characterization, temperature-dependent photoluminescence, and optical-pump terahertz-probe spectroscopy give insights into the absorption and emissive behavior of the materials as well as their charge-carrier dynamics. Overall, we further elucidate the possible reasons for the electronic and emissive properties of these intriguing materials, dominated by phonon-coupled and defect-mediated polaronic states

Directional freezing for the cryopreservation of adherent mammalian cells on a substrate

<div><p>Successfully cryopreserving cells adhered to a substrate would facilitate the growth of a vital confluent cell culture after thawing while dramatically shortening the post-thaw culturing time. Herein we propose a controlled slow cooling method combining initial directional freezing followed by gradual cooling down to -80°C for robust preservation of cell monolayers adherent to a substrate. Using computer controlled cryostages we examined the effect of cooling rates and dimethylsulfoxide (DMSO) concentration on cell survival and established an optimal cryopreservation protocol. Experimental results show the highest post-thawing viability for directional ice growth at a speed of 30 μm/sec (equivalent to freezing rate of 3.8°C/min), followed by gradual cooling of the sample with decreasing rate of 0.5°C/min. Efficient cryopreservation of three widely used epithelial cell lines: IEC-18, HeLa, and Caco-2, provides proof-of-concept support for this new freezing protocol applied to adherent cells. This method is highly reproducible, significantly increases the post-thaw cell viability and can be readily applied for cryopreservation of cellular cultures in microfluidic devices.</p></div

Transnational cryostage for directional freezing of cells adherent to a substrate.

<p>(A) Two independently controlled TECs controlled the temperatures on top of the 1.5 mm thick copper plate. “Cold” and “hot” bases of the thermal blocks separated by 2 mm slit. A motorized actuator enabled movement of the sample at a precise velocity. (B) Temperature field with a unidirectional gradient simulated with COMSOL Multiphysics. The temperature profile along the direction of the gradient displayed a steep linearity on top of the slit (inset). (C) Representative image sequence of a growing ice front in a 10% v/v DMSO solution. The front remained in the middle of the imaging frame while cells moved (displacement of a specific cell is indicated by a red arrow). The scale bar indicates 100 μm.</p

Viability of the HeLa and Caco-2 cells after directional freezing vs. non-directional slow freezing.

<p>Phase contrast images of the HeLa (left panel) and Caco-2 (right panel) cell cultures prior to freezing and 5 h after thawing. Cells frozen at 10% DMSO using a combination of directional freezing at a speed of 30 μm/sec and gradual cooling at 0.5°C/min (upper panel), or solely using gradual cooling at 0.5°C/min (lower panel). Scale bars indicate 100 μm for 10x and 50 μm for 40x magnification.</p

Quantification of cell viability.

<p><b>(</b>A) Adherent HeLa and Caco-2 cells labeled 5 h after thawing using the live/dead kit (green—<i>live</i>/ red- <i>dead</i> cells). Scale bars indicate 100 μm. (B) Quantification of live/dead labeling using flow cytometry performed on cells that were collected immediately after thawing compared the cell survival percentage obtained under combination of directional freezing and gradual cooling, non-directional gradual cooling (1°C/min) and direct freezing at a -80°C freezer.</p

Effect of the directional freezing rate on cell morphology.

<p>IEC-18 epithelial cells cultured on a cover glass were subjected to directional cooling on the translational cryostage (10% DMSO). Sample movement velocities of 10 μm/sec (eq. 1.3°C/min), 30 μm/sec (eq. 3.8°C/min), and 90 μm/sec (eq. 11.3°C/min), were tested. Then the temperature was decreased gradually to -20°C, and the cells were transferred to -80°C. (A) Ice crystal morphology as a function of the ice front propagation. Left: during the process of freezing. Right: Frozen sample at -20°C. Scale bar indicates 400 μm. (B) Phase contrast images (10x) of IEC-18 cells prior to freezing, after thawing, and after 24 h incubation post thawing in a humidified 5% CO₂ incubator at 37°C,. Scale bar indicates 100 μm.</p

IEC-18 cell monolayer morphology after directional freezing at various concentrations of DMSO in the freezing medium.

<p>(A) Ice crystals during directional freezing (velocity = 30 μm/sec, eq. 3.8°C/min) of adhered IEC-18 cells in the presence of different concentrations of DMSO (0% - 10%). Scale bar indicates 100 μm. (B) Phase contrast images of IEC-18 cells frozen in deferent concentrations of DMSO (0% - 10%) collected after thawing and 5 h incubation in a humidified 5% CO₂ incubator at 37°C. Scale bars indicate 100 μm for 10x and 25 μm for 40x magnification.</p

The effect of gradual freezing rate from -20°C to -80°C on cell morphology in a 10% DMSO medium.

<p>Following directional freezing of the adhered IEC-18 epithelial cells and gradual freezing on the translational stage to -20°C, samples were subjected to gradual cooling to -80°C on the LN flow cooling stage at rates of 0.5°C/min or 1°C/min. As a control, a sample was transferred directly to the -80°C freezer after reaching -20°C. Phase contrast images (10x) were collected prior to freezing, after thawing, and after 5 h incubation post thawing in a humidified 5% CO₂ incubator at 37°C. Scale bars indicate 100 μm.</p

Microfluidic Organ-on-a-Chip Models of Human Intestine

Microfluidic organ-on-a-chip models of human intestine have been developed and used to study intestinal physiology and pathophysiology. In this article, we review this field and describe how microfluidic Intestine Chips offer new capabilities not possible with conventional culture systems or organoid cultures, including the ability to analyze contributions of individual cellular, chemical, and physical control parameters one-at-a-time; to coculture human intestinal cells with commensal microbiome for extended times; and to create human-relevant disease models. We also discuss potential future applications of human Intestine Chips, including how they might be used for drug development and personalized medicine