Slot‐Die and Roll‐to‐Roll Processed Single Junction Organic Photovoltaic Cells with the Highest Efficiency

The record efficiency of the state‐of‐the‐art polymer solar cells (PSCs) is rapidly increasing, due to the discovery of high‐performance photoactive donor and acceptor materials. However, strong questions remain as to whether such high‐efficiency PSCs can be produced by scalable processes. This paper reports a high power conversion efficiency (PCE) of 13.5% achieved with single‐junction ternary PSCs based on PTB7‐Th, PC₇₁BM, and COi8DFIC fabricated by slot‐die coating, which shows the highest PCE ever reported in PSCs fabricated by a scalable process. To understand the origin of the high performance of the slot‐die coated device, slot‐die coated photoactive films and devices are systematically investigated. These results indicate that the good performance of the slot‐die PSCs can be due to a favorable molecule‐structure and film‐morphology change by introducing 1,8‐diiodooctane and heat treatment, which can lead to improved charge transport with reduced carrier recombination. The optimized condition is then used for the fabrication of large‐area modules and also for roll‐to‐roll fabrication. The slot‐die coated module with 30 cm² active‐area and roll‐to‐roll produced flexible PSC has shown 8.6% and 9.6%, respectively. These efficiencies are the highest in each category and demonstrate the strong potential of the slot‐die coated ternary system for commercial applications.     

Roll‐to‐Roll Printed Large‐Area All‐Polymer Solar Cells with 5% Efficiency Based on a Low Crystallinity Conjugated Polymer Blend

The challenge of continuous printing in high‐efficiency large‐area organic solar cells is a key limiting factor for their widespread adoption. A materials design concept for achieving large‐area, solution‐coated all‐polymer bulk heterojunction solar cells with stable phase separation morphology between the donor and acceptor is presented. The key concept lies in inhibiting strong crystallization of donor and acceptor polymers, thus forming intermixed, low crystallinity, and mostly amorphous blends. Based on experiments using donors and acceptors with different degree of crystallinity, the results show that microphase separated donor and acceptor domain sizes are inversely proportional to the crystallinity of the conjugated polymers. This methodology of using low crystallinity donors and acceptors has the added benefit of forming a consistent and robust morphology that is insensitive to different processing conditions, allowing one to easily scale up the printing process from a small‐scale solution shearing coater to a large‐scale continuous roll‐to‐roll (R2R) printer. Large‐area all‐polymer solar cells are continuously roll‐to‐roll slot die printed with power conversion efficiencies of 5%, with combined cell area up to 10 cm². This is among the highest efficiencies realized with R2R‐coated active layer organic materials on flexible substrate.     

The Critical Choice of PEDOT:PSS Additives for Long Term Stability of Roll‐to‐Roll Processed OPVs

The impact of additives mixed with poly(3,4‐ethylenedioxythiophene):polysty­renesulfonate (PEDOT:PSS) on the stability of organic photovoltaic modules is investigated for fully ambient roll‐to‐roll (R2R) processed indium tin oxide free modules. Four different PEDOT:PSS inks from two different suppliers are used. The modules are manufactured directly on barrier foil without a UV filter to accelerate degradation and enable completion of the study in a reasonable time span. The modules are subjected to stability testing following well‐established protocols developed by the international summit on organic photovoltaic stability (ISOS). For the harsh indoor test (ISOS‐L‐3) only a slight difference in stability is observed between the different modules. During both ISOS‐L‐3 and ISOS‐D‐3 one new failure mode is observed as a result of tiny air inclusions in the barrier foil and a R2R method is developed to detect and quantify these. During outdoor operation (ISOS‐O‐1) the use of ethylene glycol (EG) as an additive is found to drastically increase the operational stability of the modules as compared to dimethylsulfoxide (DMSO) and a new failure mode specific to modules with DMSO as the additive is identified. The data are extended in an ongoing experiment where DMSO is used as additive for long‐term outdoor testing in a solar park.     

Making Ends Meet: Flow Synthesis as the Answer to Reproducible High‐Performance Conjugated Polymers on the Scale that Roll‐to‐Roll Processing Demands

Continuous flow methods are employed for the controlled polymerization of the roll‐to‐roll (R2R) compatible polymer PBDTTTz‐4 including optimization and upscaling experiments. The polymerization rate and materials’ quality can be increased significantly with the continuous flow method where reaction times down to 10 min afforded PBDTTTz‐4 with high molecular weight and a constant quality. The flow method enables full control of the molecular weight via tuning of the flow speed, catalyst loading, and temperature and avoids variation in materials’ quality associated with conventional batch synthesis. Upscaling from 300 mg batch synthesis to 10 g flow synthesis affords PBDTTTz‐4 with a production rate of up to 120 g day^?1 for a very simple in‐house build flow reactor. An average power conversion efficiency (PCE) of 3.5% is achieved on a small scale (1 cm²) and an average PCE of 3.3% is achieved on a large scale (29 cm²). This shows that small device efficiencies can be scaled when using full R2R processing of flexible and encapsulated carbon‐based modules without the use of vacuum, indium‐tin‐oxide, or silver, with the best achieving a PCE of 3.8% PCE.     

Effect of Processing Additives on the Solidification of Blade‐Coated Polymer/Fullerene Blend Films via In‐Situ Structure Measurements

The use of processing additives has emerged as a powerful approach for the optimization of active layer performance in organic photovoltaic devices. However, definitive physical mechanisms explaining the impact of additives have not yet been determined. To elucidate the role of additives, we have studied the time evolution of structure in polymer‐fullerene films blade‐coated from additive containing solutions using in‐situ spectroscopic ellipsometry and UV–vis transmission. Additives that are poor solvents for poly(3‐hexylthiophene) (P3HT), such as 1,8‐octanedithiol, and additives that are good solvents for P3HT, such as 1‐chloronapthalene, both promote improved polymer order, phase segregation, and device performance. Regardless of the presence or type of additive, the polymer order develops under conditions of extreme supersaturation. Additives, regardless of whether they are solvents for P3HT, promote earlier polymer aggregation compared to additive ‐ free solutions presumably by degrading the solvent quality. We find evidence that the details of the final film morphology may be linked to the influence of the substrate and long‐time film plasticization in the cases of the non‐solvent and solvent respectively.     

Evaporation‐Free Nonfullerene Flexible Organic Solar Cell Modules Manufactured by An All‐Solution Process

To ensure laboratory‐to‐industry transfer of next‐generation energy harvesting organic solar cells (OSCs), it is necessary to develop flexible OSC modules that can be produced on a continuous roll‐to‐roll basis and to apply an all‐solution process. In this study, nonfullerene acceptors (NFAs)‐based donor polymer, SMD2, is newly designed and synthesized to continuously fabricate high‐performance flexible OSC modules. Also, multifunctional hole transport layers (HTLs), WO₃/HTL solar bilayer HTLs, are developed and applied via an all‐solution process called “ProcessOne” into inverted structure. SMD2, the donor terpolymer, has a deep highest occupied molecular orbital (HOMO) level and can achieve a power conversion efficiency (PCE) of 11.3% with NFAs without any pre‐/post‐treatment because of its optimal balance between crystallinity and miscibility. Furthermore, the integration of multifunctional HTLs enables the recovery of the drop in open circuit voltage (V_OC) caused by a mismatch in energy levels between the deep HOMO level of the NFAs‐based bulk‐heterojunction layer and the solution‐processed HTLs. Also, the photostability under ultraviolet‐exposure necessary for “ProcessOne” is greatly improved because of the integration of multifunctional HTLs. Consequently, because of the synergistic effects of these approaches, the flexible OSC modules fabricated in an industrial production line have a PCE of 5.25% (P_max = 419.6 mW) on an active area of 80 cm².     

Large‐Area Rolled‐Up Nanomembrane Capacitor Arrays for Electrostatic Energy Storage

The fabrication, characterization, and optimization of large area rolled‐up ultracompact nanomembrane‐based capacitor arrays is demonstrated by combining bottom‐up and top‐down fabrication methods. The scalability of the process is tested on a 4‐inch wafer platform where 1600 devices are manufactured in parallel. By using a hybrid dielectric layer consisting of HfO₂ and TiO₂ incorporated into an Al₂O₃ matrix, rolled‐up ultracompact capacitors can have their capacitance per footprint area increased by over two orders of magnitude. Their electrical properties can be precisely controlled by adjusting the oxide composition. Furthermore, the rolling of large‐area nanomembrane‐based structures naturally results in a substantial decrease of the occupied footprint area. Such electrostatic rolled‐up ultracompact energy‐storage elements have a large potential in powering various autonomous microsystems.     

Stacking interactions in RNA and DNA: Roll‐slide energy hyperspace for ten unique dinucleotide steps

Understanding dinucleotide sequence directed structures of nuleic acids and their variability from experimental observation remained ineffective due to unavailability of statistically meaningful data. We have attempted to understand this from energy scan along twist, roll, and slide degrees of freedom which are mostly dependent on dinucleotide sequence using ab initio density functional theory. We have carried out stacking energy analysis in these dinucleotide parameter phase space for all ten unique dinucleotide steps in DNA and RNA using DFT‐D by ωB97X‐D/6‐31G(2d,2p), which appears to satisfactorily explain conformational preferences for AU/AU step in our recent study. We show that values of roll, slide, and twist of most of the dinucleotide sequences in crystal structures fall in the low energy region. The minimum energy regions with large twist values are associated with the roll and slide values of B‐DNA, whereas, smaller twist values correspond to higher stability to RNA and A‐DNA like conformations. Incorporation of solvent effect by CPCM method could explain the preference shown by some sequences to occur in B‐DNA or A‐DNA conformations. Conformational preference of BII sub‐state in B‐DNA is preferentially displayed mainly by pyrimidine–purine steps and partly by purine–purine steps. The purine–pyrimidine steps show largest effect of 5‐methyl group of thymine in stacking energy and the introduction of solvent reduces this effect significantly. These predicted structures and variabilities can explain the effect of sequence on DNA and RNA functionality. © 2014 Wiley Periodicals, Inc. Biopolymers 103: 134–147, 2015.     

Slot‐Die Coating of a High Performance Copolymer in a Readily Scalable Roll Process for Polymer Solar Cells

Copolymers based on dithieno[3,2‐b:2′,3′‐d]silole (DTS) and dithienylthiazolo[5,4‐d]thiazole (TTz) are synthesized and tested in an all‐solution roll process for polymer solar cells (PSCs). Fabrication of polymer:[6,6]‐phenyl‐C₆₁‐butyric acid methyl ester (PCBM) solar cells is done on a previously reported compact coating/printing machine, which enables the preparation of PSCs that are directly scalable with full roll‐to‐roll processing. The positioning of the side‐chains on the thiophene units proves to be very significant in terms of solubility of the polymers and consequently has a major impact on the device yield and process control. The most successful processing is accomplished with the polymer, PDTSTTz‐4 , that has the side‐chains situated in the 4‐position on the thiophene units. Inverted PSCs based on PDTSTTz‐4 demonstrate high fill factors, up to 59%, even with active layer thicknesses well above 200 nm. Power conversion efficiencies of up to 3.5% can be reached with the roll‐coated PDTSTTz‐4 :PCBM solar cells that, together with good process control and high device yield, designate PDTSTTz‐4 as a convincing candidate for high‐throughput roll‐to‐roll production of PSCs.     

HS‐SPME‐GC‐FID method for detection and quantification of Bacillus cereus ATCC 10702 mediated 2‐acetyl‐1‐pyrroline

A rapid micro‐scale solid‐phase micro‐extraction (SPME) procedure coupled with gas‐chromatography with flame ionized detector (GC‐FID) was used to extract parts per billion levels of a principle basmati aroma compound “2‐acetyl‐1‐pyrroline” (2‐AP) from bacterial samples. In present investigation, optimization parameters of bacterial incubation period, sample weight, pre‐incubation time, adsorption time, and temperature, precursors and their concentrations has been studied. In the optimized conditions, detection of 2‐AP produced by Bacillus cereus ATCC10702 using only 0.5 g of sample volume was 85 μg/kg. Along with 2‐AP, 15 other compounds produced by B. cereus were also reported out of which 14 were reported for the first time consisting mainly of (E)?2‐hexenal, pentadecanal, 4‐hydroxy‐2‐butanone, n‐hexanal, 2–6‐nonadienal, 3‐methoxy‐2(5H) furanone and 2‐acetyl‐1‐pyridine and octanal. High recovery of 2‐AP (87 %) from very less amount of B. cereus samples was observed. The method is reproducible fast and can be used for detection of 2‐AP production by B. cereus. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:1356–1363, 2014