Scaling Up ITO‐Free Solar Cells

Indium‐tin‐oxide‐free (ITO‐free) polymer solar cells with composite electrodes containing current‐collecting grids and a semitransparent poly(3,4‐ethylenedioxythiophene):polystyrenesulfonate) (PEDOT:PSS) conductor are demonstrated. The up‐scaling of the length of the solar cell from 1 to 6 cm and the effect of the grid line resistance are explored for a series of devices. Laser‐beam‐induced current (LBIC) mapping is used for quality control of the devices. A theoretical modeling study is presented that enables the identification of the most rational cell dimension for the grids with different resistances. The performance of ITO‐free organic solar cells with different dimensions and different electrode resistances are evaluated for different light intensities. The current generation and electric potential distribution are found to not be uniformly distributed in large‐area devices at simulated 1 Sun illumination. The generated current uniformity increases with decreasing light intensities.     

A Metal‐Free and Biotically Degradable Battery for Portable Single‐Use Applications

This article presents a new approach for environmentally benign, low‐cost batteries intended for single‐use applications. The proposed battery is designed and fabricated using exclusively organic materials such as cellulose, carbon, and wax and features an integrated quinone‐based redox chemistry to generate electricity within a compact form factor. This primary capillary flow battery is activated by the addition of a liquid sample and has shown continuous operation up to 100 min with an output voltage that can be conveniently scaled to match the voltage needs of portable electronic devices (1.5–3.0 V). Once depleted, the battery can be disposed of without the need for any recycling facility, as its components are nontoxic and shown to be biotically degradable in a standardized test. The practical utility of the battery is demonstrated by direct substitution of a lithium ion coin cell in a diagnostic application.     

Microfluidic device‐assisted etching of p‐HEMA for cell or protein patterning

The construction of biomaterials with which to limit the growth of cells or to limit the adsorption of proteins is essential for understanding biological phenomena. Here, we describe a novel method to simply and easily create thin layers of poly (2‐hydroxyethyl methacrylate) (p‐HEMA) for protein and cellular patterning via etching with ethanol and microfluidic devices. First, a cell culture surface or glass coverslip is coated with p‐HEMA. Next, a polydimethylsiloxane (PDMS) microfluidic is placed onto the p‐HEMA surface, and ethanol is aspirated through the device. The PDMS device is removed, and the p‐HEMA surface is ready for protein adsorption or cell plating. This method allows for the fabrication of 0.3 µm thin layers of p‐HEMA, which can be etched to 10 µm wide channels. Furthermore, it creates regions of differential protein adhesion, as shown by Coomassie staining and fluorescent labeling, and cell adhesion, as demonstrated by C2C12 myoblast growth. This method is simple, versatile, and allows biologists and bioengineers to manipulate regions for cell culture adhesion and growth. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:243–248, 2018     

Design‐to‐Device Approach Affords Panchromatic Co‐Sensitized Solar Cells

Data‐driven materials discovery has become increasingly important in identifying materials that exhibit specific, desirable properties from a vast chemical search space. Synergic prediction and experimental validation are needed to accelerate scientific advances related to critical societal applications. A design‐to‐device study that uses high‐throughput screens with algorithmic encodings of structure–property relationships is reported to identify new materials with panchromatic optical absorption, whose photovoltaic device applications are then experimentally verified. The data‐mining methods source 9431 dye candidates, which are auto‐generated from the literature using a custom text‐mining tool. These candidates are sifted via a data‐mining workflow that is tailored to identify optimal combinations of organic dyes that have complementary optical absorption properties such that they can harvest all available sunlight when acting as co‐sensitizers for dye‐sensitized solar cells (DSSCs). Six promising dye combinations are shortlisted for device testing, whereupon one dye combination yields co‐sensitized DSSCs with power conversion efficiencies comparable to those of the high‐performance, organometallic dye, N719. These results demonstrate how data‐driven molecular engineering can accelerate materials discovery for panchromatic photovoltaic or other applications.     

Microfluidic synthesis of composite cross‐gradient materials for investigating cell–biomaterial interactions

Combinatorial material synthesis is a powerful approach for creating composite material libraries for the high‐throughput screening of cell–material interactions. Although current combinatorial screening platforms have been tremendously successful in identifying target (termed “hit”) materials from composite material libraries, new material synthesis approaches are needed to further optimize the concentrations and blending ratios of the component materials. Here we employed a microfluidic platform to rapidly synthesize composite materials containing cross‐gradients of gelatin and chitosan for investigating cell–biomaterial interactions. The microfluidic synthesis of the cross‐gradient was optimized experimentally and theoretically to produce quantitatively controllable variations in the concentrations and blending ratios of the two components. The anisotropic chemical compositions of the gelatin/chitosan cross‐gradients were characterized by Fourier transform infrared spectrometry and X‐ray photoelectron spectrometry. The three‐dimensional (3D) porous gelatin/chitosan cross‐gradient materials were shown to regulate the cellular morphology and proliferation of smooth muscle cells (SMCs) in a gradient‐dependent manner. We envision that our microfluidic cross‐gradient platform may accelerate the material development processes involved in a wide range of biomedical applications. Biotechnol. Bioeng. 2011; 108:175–185. © 2010 Wiley Periodicals, Inc.     

Dopant‐Free Hole Transporting Polymers for High Efficiency,Environmentally Stable Perovskite Solar Cells

Over the past five years, a rapid progress in organometal‐halide perovskite solar cells has greatly influenced emerging solar energy science and technology. In perovksite solar cells, the overlying hole transporting material (HTM) is critical for achieving high power conversion efficiencies (PCEs) and for protecting the air‐sensitive perovskite active layer. This study reports the synthesis and implementation of a new polymeric HTM series based on semiconducting 4,8‐dithien‐2‐yl‐benzo[1,2‐d;4,5‐d′]bistriazole‐alt‐benzo[1,2‐b:4,5‐b′]dithiophenes (pBBTa‐BDTs), yielding high PCEs and environmentally‐stable perovskite cells. These intrinsic (dopant‐free) HTMs achieve a stabilized PCE of 12.3% in simple planar heterojunction cells—the highest value to date for a polymeric intrinsic HTM. This high performance is attributed to efficient hole extraction/collection (the most efficient pBBTa‐BDT is highly ordered and orients π‐face‐down on the perovskite surface) and balanced electron/hole transport. The smooth, conformal polymer coatings suppress aerobic perovskite film degradation, significantly enhancing the solar cell 85 °C/65% RH PCE stability versus typical molecular HTMs.     

Spontaneous Growth of 3D Framework Carbon from Sodium Citrate for High Energy‐ and Power‐Density and Long‐Life Sodium‐Ion Hybrid Capacitors

Carbon sheets with 3D architectures, large graphitic interlayer spacing, and high electrical conductivity are highly expected to be an ideal anode material for sodium‐ion hybrid capacitors (SIHCs). Pursuing a simple synthesis methodology and advancing it from the laboratory to industry is of great importance. In this study, a new approach is presented to prepare 3D framework carbon (3DFC) with the above integrated advantages by a direct calcination of sodium citrate without aid of any additional carbon source, template, or catalyst. The first‐principle calculations verify that the large interlayer spacing and the curvature structure of 3DFC facilitate the sodium ion insertion/extraction. As a consequence, the optimal 3DFC sample exhibits high reversible capacity as well as excellent rate and cycling performance. On this basis, a dual‐carbon SIHC is fabricated by employing 3DFC as battery‐type anode and 3DFC‐derived nanoporous carbon as capacitor‐type cathode. It is able to deliver high energy‐ and power‐density feature as well as outstanding long‐term cycling stability in the potential range of 0–4.0 V. This study may open an avenue for developing high‐performance carbon electrode materials and pushes the practical applications of SIHCs a decisive step forward.     

High Efficiency (>17%) Si‐Organic Hybrid Solar Cells by Simultaneous Structural,Electrical, and Interfacial Engineering via Low‐Temperature Processes

Highly efficient organic–inorganic hybrid solar cells of Si‐poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) have been demonstrated by simultaneous structural, electrical, and interfacial engineering with low processing temperature. Si substrate has been sculpted into hierarchical structure to reduce light reflection loss and increase interfacial junction area at the same time. Regarding the electrical optimization, highly conductive organic PEDOT:PSS layer has been formulated with low sheet resistance. It is argued that the sheet resistance, rather than conductivity, is the primary parameter for the high efficiency hybrid cells, which leads to the optimization of thickness, i.e., thick enough to have low sheet resistance but transparent enough to pass the incident sunlight. Finally, siloxane oligomers have been inserted into top/bottom interfaces by contact‐printing at room ambient, which suppresses carrier recombination at interfaces and reduces contact resistance at bottom electrode. Contrary to high‐temperature doping (for the formation of front surface or back surface fields), wet solution processes or vacuum‐based deposition, the contact‐printing can be done at room ambient to reduce carrier recombination at the interfaces. The high efficiency obtained with low processing temperature can make this type of cells be a possible candidate for post‐Si photovoltaics.     

Metal‐Oxide‐Free Methylammonium Lead Iodide Perovskite‐Based Solar Cells: the Influence of Organic Charge Transport Layers

Metal‐oxide‐free methylammonium lead iodide perovskite‐based solar cells are prepared using a dual‐source thermal evaporation method. This method leads to high quality reproducible films with large crystal domain sizes allowing for an in depth study of the effect of perovskite film thickness and the nature of the electron and hole blocking layers on the device performance. The power conversion efficiency increases from 4.7% for a device with only an organic electron blocking layer to almost 15% when an organic hole blocking layer is also employed. In addition to the in depth study on small area cells, larger area cells (approx. 1 cm^?2) are prepared and exhibit efficiencies in excess of 10%.     

Cyanobacterial dynamics in shallow Lake Apopka (Florida,U.S.A.) before and after the shift from a macrophyte‐dominated to a phytoplankton‐dominated state

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A Calcium‐Ion Hybrid Energy Storage Device with High Capacity and Long Cycling Life under Room Temperature

Ca‐ion based devices are promising candidates for next‐generation energy storage with high performance and low cost, thanks to its multielectrons, superior kinetics, as well as abundance (2500 times lithium). Because of the lack of an appropriate combination of suitable electrode materials and electrolytes, it is unsuccessful to attain a satisfactory performance on complete Ca‐ion energy storage devices. Here, the multiion reaction strategy is defined to construct a complete Ca‐ion energy storage device and a capacitor–battery hybrid mechanism is deliberately adopted. Profiting from the elaborate design, it exhibits a high reversible capacity of 92 mAh g^?1, unmatchable rate capability, and a high capacity retention of 84% over 1000 cycles under room temperature, which is the best performance of reported Ca‐based energy storage devices.     

Morphology‐Dependent Trap Formation in High Performance Polymer Bulk Heterojunction Solar Cells

Bulk heterojunction solar cells (BHJs) based on poly[N‐9″‐hepta‐decanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT) can have internal quantum efficiencies approaching 100% but require active layers that are too thin to absorb more than ～70% of the above band gap light. When the active layer thickness is increased so that the cell absorbs more light, the fill factor and open circuit voltage decrease rapidly, so that the overall power conversion efficiency decreases. We find that hole‐traps in the polymer, which we characterize using space‐charge limited current measurements, play an important role in the performance of PCDTBT‐based BHJs and may limit the active layer thickness. Recombination due to carrier trapping is not often considered in BHJs because it is not believed to be a dominant loss mechanism in the “fruit‐fly” P3HT system. Furthermore, we show that in contrast to P3HT, PCDTBT has only weak short‐range molecular order, and that annealing at temperatures above the glass transition decreases the order in the π–π stacking. The decrease in structural order is matched by the movement of hole‐traps deeper into the band gap, so that thermal annealing worsens hole transport in the polymer and reduces the efficiency of PCDTBT‐based BHJs. These findings suggest that P3HT is not prototypical of the new class of high efficiency polymers, and that further improvement of BHJ efficiencies will necessitate the study of high efficiency polymers with low structural order.