The quest for sustainable energy solutions is critical amidst environmental challenges. Thermoelectric (TE) devices present a promising approach by converting waste heat into electricity through the Seebeck effect. These devices are advantageous due to their direct energy conversion, solid-state construction, reliability, scalability, long lifespan, and compatibility. However, their efficiency is often low, and they heavily depend on rare, expensive, and toxic inorganic materials. Carbon-based thermoelectric materials, such as carbon allotropes and organic thermoelectric materials such as conductive polymers, offer a sustainable alternative due to their abundance, low cost, eco-friendliness, and high mechanical flexibility, though their efficiency requires improvement. This study explores two generations of thermoelectric materials combining sulfonated-poly(3,4-ethylenedioxythiophene) (PSEDOT), a water-soluble and self-doped polymer, and single-walled carbon nanotubes (SWCNTs). The first generation optimized SWCNT dispersion and purification conditions, while the second generation improved the performance using better materials, resulting in a flexible film with a high conductivity (2000 S cm-1) and a power factor of 96.8 mu W m-1 K-2.

ABSTRACT Our group has recently demonstrated the first fully solution‐processed polymeric multilayer piezoelectric devices. The key challenge, that is, the effective control of the redissolution issue, has been overcome using a solvent that offers adequate solubility but extremely slow dissolution for the piezoelectric polymer, poly(vinylidene fluoride‐trifluoroethylene) [P(VDF‐TrFE)]. Several qualified solvents have been identified. Here, we comparatively study the effects of solvents on piezoelectric performance and production yield, for choosing the right solvent for fully solution‐processed multilayer piezoelectric devices. Each solvent exhibits distinct yield dependence on drying temperature, but the maximal yields achieved are independent of processing solvents. The solvents are also found to be interchangeable in terms of piezoelectric performance. The drying temperature and final annealing temperatures are identified to be decisive factors. The former only impacts the yield, and the latter only impacts the performance. The three parameters that define a poling condition are all investigated for the first time. A procedure enabling a fast identification of the right poling condition is proposed. Fully solution‐processed P(VDF‐TrFE) multilayer piezoelectric devices are prepared using the optimized conditions, and the dependence of the performance and yield on the number of layers is demonstrated. This work lays the foundation for producing such devices for practical applications.

Bulk heterojunction (BHJ) organic solar cells based on p-type polymers and n-type fullerene derivatives have attracted increasing attention due to their promising potential for providing low–cost solar electricity. In this paper, we will introduce our recent work on the development of new fullerene derivatives. Through Rh complex catalyzed coupling reactions and cycloaddition reactions, we attached several organic functional groups to the fullerene skeleton. It was found that the organic substituents had little impact on the fullerene energy levels. Instead, the organic substituents have huge impact on the other physical properties of the resulting fullerene derivatives, such as solubility, crystallinity, and electron mobility. We designed and synthesized a novel series of alkoxy substituted indene derivatives as solubilizing groups for fullerenes. Preliminary experimental results demonstrated that these 5 alkoxyindene modified C70 derivatives are superior to widely used PC71BM when blended with poly[N-heptadecanyl-2,7 carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'- benzothiadiazole)] (PCDTBT) in BHJ solar cells. The device series resistance decreased from 10 cm2 for the PC71BM based device to 4 cm2 for the 5-methoxyindene-C70 monoadduct based device. As a result, the device fill factor increased from 0.60 to 0.69, and the overall EQE-calibrated power conversion efficiency was enhanced from 5.6% to 6.2%.

Extending the number of fused aromatic rings in & pi;-conjugated materials has proven to be an effective strategy to tailor the electronic, optical, and structural properties. In this work, the structure of the well-known Y6 was modified and a new asymmetric non-fullerene acceptor BIID was developed for organic photovoltaics. BIID was found to show a slightly blue-shifted absorption spectrum compared with Y6 in solid thin films. A high efficiency of 19.5% was achieved by using an BIID:PM6 bulk heterojunction blend film in a 1 cm2 device under indoor LED light, while an efficiency of 17.6% was achieved from the Y6:PM6 blend under the same conditions. Several characterization techniques were applied to study the structure-property relationships, and it was found that the BIID:PM6 blend has less trap-induced recombination, which led to a much higher open circuit voltage and higher device efficiency. With numerous possibilities for further structural optimization, such as attaching various substituents to the central electron-deficient core, BIID is considered to be a class of promising non-fullerene acceptors for indoor organic photovoltaics.

We demonstrate large-area (1 cm2) organic photovoltaic (OPVs) devices based on bis(tri-n-butylsilyl oxide) silicon phthalocyanine (3BS)2-SiPc as a non-fullerene acceptor (NFA) with low synthetic complexity paired with poly(3-hexylthiophene) (P3HT) as a donor polymer. Environment-friendly nonhalogenated solvents were used to process large area OPVs on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates. An alternate sequentially (Alt-Sq) blade-coated active layer with bulk heterojunction-like morphology is obtained when using (3BS)2-SiPc processing with o-xylene/1,3,5-trimethylbenzene solvents. The sequential (Sq) active layer is prepared by first blade-coating (3BS)2-SiPc solution followed by P3HT coated on the top without any post-treatment. The conventional sequentially (Sq) blade-coated active layer presents very low performance due to the (3BS)2-SiPc bottom layer being partially washed off by processing the top layer of P3HT. In contrast, alternate sequentially (Alt-Sq) blade-coated layer-by-layer film shows even better device performance compared to the bulk heterojunction (BHJ) active layer. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) and atomic force microscopy (AFM) reveal that the Alt-Sq processing of the active layer leads to a BHJ-like morphology with a well-intermixed donor-acceptor component in the active layer while providing a simpler processing approach to low-cost and large-scale OPV production.

Silicon phthalocyanines as ternary additives are a promising way to increase the performance of organic photovoltaics. The miscibility of the additive and the donor polymer plays a significant role in the enhancement of the device performance, therefore, ternary additives can be designed to better interact with the conjugated polymer. We synthesized N-9'-heptadecanyl-2,7-carbazole functionalized SiPc ((CBzPho)2-SiPc), a ternary additive with increased miscibility in poly[N-90-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT). The resulting additive was included into PCDTBT and [6,6]-phenyl C71 butyric acid methyl ester as bulk (PC71BM) heterojunction OPV devices as a ternary additive. While the (CBzPho)2-SiPc demonstrated strong EQE >30% contribution in the range of 650-730 nm, the overall performance was reduced because (CBzPho)2-SiPc acted as a hole trap due to its high-lying HOMO energy level. This study demonstrates the importance of the solubility, miscibility, and energy level engineering of the ternary additive when designing organic photovoltaic devices.

A new type of printed capacitive humidity sensors with stacked parallel-plate electrodes is presented in this work. The high capacitance and high sensitivity associated with this type of sensors allow the use of low-cost electronic circuits for detection. The use of a polymer sensing material with extremely low hysteresis and a grid top electrode design ensures the sensor’s stable performance and rapid response to humidity changes. Our study shows that the sensor performance can be significantly improved through printing processes and the performance is affected by environment temperature through its influence on water sorption in the sensing material. The temperature effect on the sensors was investigated in detail and the sorption heat of water molecules in the sensing material was estimated. The printed sensor was attached to a printed circuit board (PCB) to become a standalone and functional sensing unit. The PCB board is equipped with light energy harvesting, capacitance measurement, and wireless data transmission, as well as the calibration capability for converting measured capacitance to relative humidity. The obtained unit met the needs for application in high performance building management.

We report an investigation into the impact of applying a large reverse bias voltage during current-voltage (J-V) sweeps on the degradation rate of solar cells based on poly[N-9 ''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6-6]-phenyl C71-butyric acid methyl ester (PC70BM), under air mass 1.5 simulated solar irradiation. The degradation rate was found to be significantly slower when devices were characterized using frequent J-V sweeps with a large reverse bias component (-7 V to 1 V), with a decrease in power conversion efficiency of 24% after similar to 100 hrs of light exposure. In contrast, devices scanned from-1 V to 1 V degrade by 72% in the same time period. The decay in the photovoltaic performance was found to be related to an increase in the series resistance and a decrease in the shunt resistance of the devices over time. Further characterization of the bulk heterojunction layer under irradiation conditions indicates that this behavior might be caused by the decreasing mobility of the charge carriers due to the formation of the defects or traps in the layer, induced by the photo-oxidation process. The frequent application of a large reverse bias sweep most likely helps de-trap the charge carriers and slows down the device degradation. Impedance analysis indicated that during the decay of PCDTBT:PC70BM devices the bulk layer became more resistive with time, and applying large and frequent reverse bias sweeps during testing could significantly slow down this process. The charge carrier extraction time was found to increase from 7 mu s to more than 400 mu s after photo-degradation. These findings demonstrate that repeated application of a reverse bias voltage can affect device degradation, and therefore that the specific details of J-V characterization should be reported alongside device lifetime claims.

As we move toward roll‐to‐roll processing of organic photovoltaics (OPVs), it is important to validate the process and the ink formulations. A poly[[9‐(1‐octylnonyl)‐9Hcarbazole‐2,7‐diyl]‐2,5‐thiophenediyl‐2,1,3‐benzothiadiazole‐4,7 diyl2,5thiophenediyl]:[6,6]‐phenyl C71 butyric acid methyl ester (PCDTBT:PC 71 BM)‐based OPV with an increase in power conversion efficiency (PCE) from 4.6% up to 5.4% by incorporating bis(tri‐hexylsiloxy) silicon phthalocyanine ((3HS)2‐SiPc) NIR absorbing ternary additives on indium tin oxide (ITO)/polyethyleneterapthalate (PET) flexible substrate with active area of 1 cm 2 under simulated AM 1.5G one sun irradiation. Maximum PCE of the ternary OPVs was obtained with 5 wt% of (3HS) 2 ‐SiPc added when processing the active layer by spin coating, whereas the addition of 10 wt% of (3HS) 2 ‐SiPc is required for the maximization of PCE when processing the films by blade coating. The importance of processing conditions when optimizing the concentration of ternary additives in bulk heterojunction (BHJ) OPVs is demonstrated.

The synthesis of 4,4'-difluoro-2,2'-bithiophene is reported and an alternating donor-acceptor copolymer of this moiety and diketopyrrolopyrrole has been prepared. This polymer has a lower highest occupied molecular orbital than its non-fluorinated analogue polymer. Organic thin film transistors based on this polymer showed p-type charge transport behavior and a hole mobility of 0.21 cm(2) V-1 s(-1) in bottom-gate bottom-contact devices. Organic solar cells using this polymer as donor and [6,6]-Phenyl-C-71-butyric acid methyl ester as acceptor achieved a power conversion efficiency of 3.4% with a high fill factor of 69%. Our morphology analysis showed that there was a lack of long-range ordered structure in the neat polymer thin film, which could cause the inferior device performance.

The mass production of organic photovoltaics requires high throughput processes capable of producing a functional active layer which is homogenous, pinhole free and of a specified thickness. Common methods to achieve this are slot-die coating and gravure printing. We have demonstrated the fabrication of poly(N-9'heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2', 1',3'-benzothiadiazole (PCDTBT) based photovoltaic cells using the flexographic printing technique, which enables high throughput patterned active layers to be deposited on flexible substrates at lower cost. This was achieved by optimizing the flexographic plate pattern, print speed, the solvent and the drying process. By incorporating halftone patterning, a common process in the graphics printing industry, and optimizing the printing speed, the homogeneity of the active layer print was significantly improved. Further studies of suitable solvents and drying conditions led to reduced pinhole formation and improved uniformity. The functionality of the flexographically printed active layer was demonstrated by fabrication of 1 cm(2) photovoltaic cells which showed an efficiency of up to 3.5%, which is comparable to alternative deposition techniques. These results demonstrate the suitability of flexography as a fabrication technique for bulk heterojunction organic photovoltaics.

A high density wireless environmental sensor network has great potential to provide enhanced control options to building automation systems to reduce energy consumption and thus GHG emissions. In this work, we have developed light sensors and temperature sensors with solar energy harvesting and wireless communication capability for the application. The hybrid sensors are built by integrating printed sensing elements with EnOcean's technology that provides solar energy harvesting and wireless transmission functions. The light sensing and temperature sensing elements were printed on flexible PET films using organic photosensitive materials and particle-filled polymer inks developed by our team. The resulting hybrid sensors were tested and shown to meet design specifications. The light sensors have been installed in a full-scale office test bed for demonstrating efficient light control.

In this talk, I will introduce the research activities on the development of printed flexible organic solar panels, field effect transistors, and pMOS based logic circuits under NRC’s Printable Electronics Flagship Program. I will report the development of polycarbazole-based, printed organic solar panels and the application of a printable, air-stable, and annealing-free zinc oxide nanoparticle (ZnO NP) solution in the fabrication of inverted bulk heterojunction solar cells. The as-coated ZnO thin films are insoluble in organic solvents and can be directly used as an electron extraction layer in solar cells. The process is R2R compatible. Our non-encapsulated inverted solar cells are highly stable with their PCEs remaining unchanged after being stored in air for more than 50 days. The development of inkjet-printed pMOS inverters and logic gates on flexible substrates will be also presented. The fabrication of inkjet-printed OTFTs has achieved a yield of 97%. Different types of logic gates, inverters, and ring oscillators have been successfully fabricated by using these basic pMOS devices.

In this paper we report on the synthesis and development of vanadium oxide precursor flexographic ink for the printing of hole-transporting layers in organic solar cells. For the synthesis of vanadium oxide inks, a sol-gel methodology was utilized. By modifying the vanadium alkoxide precursor with a right type of coordinating ligands a stable and flexoprintable ink has been successfully developed. Flexo-printing afforded smooth and uniform vanadium oxide sol-gel films on top of PCDTBT:PC70BM films. The conversion of the synthesized sol-gel film into a corresponding vanadium oxide layer was followed by DSC/TGA and XPS analyses. The inks were used for the fabrication of inverted organic solar cells by flexo-printing. Power conversion efficiencies ranging between 3.5 % and 4.5 % were achieved, which are slightly lower than the reference cells using vacuum-deposited MoO3 as the hole-transporting layers.

We report the development and application of high-quality zinc oxide nanoparticles (ZnO NPs) processed in air for stable inverted bulk heterojunction solar cells as an electron extraction layer (EEL). The ZnO NPs (average size ∼11 nm) were dispersed in chloroform and stabilized by propylamine (PA). We demonstrated that the ZnO NP dispersion with 4 vol.% of PA as stabilizer can be used in air directly and remains clear up to one month after preparation. Our inverted solar cells consisted of a blade-coated poly(N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole (PCDTBT) and [6,6]-phenyl C71-butyric acid methyl ester (PC71BM) (1: 4 by weight) active layer sandwiched between a ZnO electron extraction layer and a MoO3/Ag anode. All solar cells with ZnO films fabricated in air using PA-stabilized ZnO dispersions prepared within a time window of one month exhibited power conversion efficiencies (PCE) above 4%. In contrast, if the ZnO film was prepared in air using regular un-stabilized ZnO NP dispersion, the PCE would drop to 0.2% due to poor film quality. More interestingly, X-ray photoelectron spectroscopy and nuclear magnetic resonance measurements indicated that the PA ligands were not covalently bonded to ZnO NPs and did not exist in the deposited ZnO films. The spin-cast ZnO thin films (without any thermal treatment) are insoluble in organic solvents and can be directly used as an EEL in solar cells. This feature is beneficial for fabricating organic solar cells on flexible polymer substrates. More importantly, our non-encapsulated inverted solar cells are highly stable with their PCEs remaining unchanged after being stored in air for 50 days.

The evolution of extravagant sexual traits by sensory exploitation occurs if males incidentally evolve features that stimulate females owing to a pre‐existing environmental response that arose in the context of natural selection. The sensory exploitation process is thus expected to leave a specific genetic imprint, a pleiotropic control of the original environmental response and the novel sexual response in females. However, females may be subsequently selected to improve their discrimination of environmental and sexual stimuli. Accordingly, responses may have diverged and the original genetic architecture may have been modified. These possibilities may be considered by studying the genetic architecture of responses to male signals and to the environmental stimuli that were purportedly ‘exploited’ by those signals. However, no previous study has addressed the genetic control of sensory exploitation. We investigated this question in an acoustic pyralid moth, Achroia grisella, in which a male ultrasonic song attracts females and perception of ultrasound likely arose in the context of detecting predatory bats. We examined the genetic architecture of female response to bat echolocation signals and to male song via a cartographic study of quantitative trait loci (QTL) influencing these receiver traits. We found several QTL for both traits, but none of them were colocalized on the same chromosomes. These results indicate that – to the extent to which male A. grisella song originated by the process of sensory exploitation – some modification of the female responses occurred since the origin of the male signal.