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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

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 ∼ 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 μs to more than 400 μs 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 isimportant to validate the process and the ink formulations. A poly[[9-(1-octyl-nonyl)-9Hcarbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7diyl2,5thiophenediyl]:[6,6]-phenyl C71 butyric acid methyl ester (PCDTBT:PC₇₁BM)-based OPV with an increase in power conversion efficiency (PCE) from4.6% up to 5.4% by incorporating bis(tri-hexylsiloxy) silicon phthalocyanine((3HS)2-SiPc) NIR absorbing ternary additives on indium tin oxide (ITO)/poly-ethyleneterapthalate (PET)flexible substrate with active area of 1 cm² undersimulated AM 1.5G one sun irradiation. Maximum PCE of the ternary OPVs wasobtained with 5 wt% of (3HS)₂-SiPc added when processing the active layer byspin coating, whereas the addition of 10 wt% of (3HS)2-SiPc is required for themaximization of PCE when processing thefilms by blade coating. The importanceof processing conditions when optimizing the concentration of ternary additivesin bulk heterojunction (BHJ) OPVs is demonstrated.

The synthesis of 4,4ʹ-difluoro-2,2ʹ-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 cm2 V−1 s−1 in bottom-gate bottom-contact devices. Organic solar cells using this polymer as donor and [6,6]-Phenyl-C71-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.

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., 2018 International Flexible Electronics Technology Conference (IFETC), August 7-9, 2018, Ottawa, ON, Canada

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%., International Conference on Renewable Energies and Power Quality (ICREPQ’18), March 21-23, 2018, Salamanca, Spain

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 cm2 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.

We report the effect of thermal annealing and quenching on the film morphology and device performance of polymer light-emitting electrochemical cells (LECs). The polymer films of LECs consist of a luminescent polymer, an ion-conducting polymer, and a lithium salt. The LECs studied have an extremely large planar configuration, which enables time-resolved fluorescence imaging of both doping and emission profiles of the devices. Annealing at temperatures above 350 K leads to the disappearance of many visible “white dots” initially present in the LEC film, and a much smoother surface. Annealed and quenched devices exhibit dramatically improved initial and peak current, peak electroluminescence (EL) intensity, doping propagation speed and response time. In addition, the emission zone of annealed devices is more centered than un-annealed devices. These improvements are attributed to the melting of electrolyte domains in the LEC film, which leads to better film quality and enhanced ion conductivity. Our results demonstrate that the simple annealing/quenching technique can be used to achieve the desired phase morphology in LEC films, which are often severely phase-separated due to incompatibility between the luminescent polymer and the electrolyte polymer.

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., Oxide-Based Materials and Devices VI, February 8-11, 2015, Series: Proceedings of SPIE; no. 9364

Organic photovoltaic devices offer a large technological potential as a renewable source of electrical energy because of their low cost and ease of processing. For the last few years, the interest in such devices has grown rapidly, allowing multiplication of the solar conversion efficiency by 5 within about 10years. The highest conversion efficiency obtained is now close to 5% with a spin-coated polythiophene-fullerene blend. For a better understanding of those polymer blend systems, we have fabricated a coevaporated solar cell from model molecules. The molecular blend was composed of sexithiophene (α,α′-dihexylsexithiophene, T6) as a donor and fullerene C60 as an acceptor. The influence of the T6:C60 proportion was studied for an active layer of 100nm thickness. The conversion efficiency obtained with the optimal proportion of T6:C60 (40–60) is 0.7%. Reverse bias annealing effect was studied by measuring the current-voltage characteristics after each postprocessing step. The conversion efficiency reached 1% but still remained much less than for the polymer bulk heterojunction. This major difference may come from the spontaneous phase separation which takes place in polymers to form an interpenetrated network.

Organic field-effect transistors were fabricated where the active semiconductor layer consisted of a co-evaporated film of pentacene and a perylene derivative, N,N′-ditridecylperylene-3,4,9,10-tetracarboxylic diimide. The device characteristics were evaluated in an oxygen-free environment. The field-effect transistor showed excellent ambipolar operation with field-effect hole mobility of 0.09 cm2 V−1 s−1 and field-effect electron mobility of 9.3 × 10−3 cm2 V−1 s−1. The threshold voltage for p-channel operation was −18 V and the same for n-channel operation was 15 V. This ambipolar device could be a building block to form flexible integrated circuits with low-power consumption and ease of design.

We developed indium-tin-oxide/perylene diimide (or bathocuproine (BCP))/poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) and [6,6]-phenyl C60 butyric acid methyl ester (PCBM) blend/copper phthalocyanine (CuPc)/Au interpenetrated network polymer solar cells in order to improve air stability. The stability properties of the cells were characterized by current–voltage measurements under the influence of light and air. We achieved long lifetime solar cells which work at least 2 weeks under ambient air conditions without encapsulation. Solar energy conversion efficiency of the cells decrease 30% of the first day value at the end of 2 weeks. Photocurrent absorption properties of the devices were also investigated.

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.

Organic solar cells based on an interpenetrated network of conjugated polymer as donor and fullerene derivative as acceptor materials have a great potential for improving efficiency. We fabricated a device based on a composite of poly(2-methoxy-5-(2′-ethylhexyloxy)-1, 4-phenylenevinylene and [6,6]-phenyl C60 butyric acid methyl ester. Surface treatment, insertion of interfacial layers, and improvement of the morphology of the active layer significantly increase the photovoltaic performances of the structure. We obtain an open circuit voltage of 0.87 V and short circuit current density of 8.4 mA/cm2 under 100 mW/cm2 air-mass 1.5 solar simulator illumination, yielding a 2.9% power conversion efficiency.

We report the investigation of the air photostability of benzo[1,2-b:4,5-b']dithiophene (BDT) based conjugated polymers using UV-visible spectroscopy, X-ray photoelectron spectroscopy, gel permeation chromatography, and nuclear magnetic resonance spectroscopy. Three low band gap alternating D-A copolymers consisting of 3-fluoro-2-heptylcarbonylthieno[3,4-b]thiophene and alkyl-substituted BDT, alkoxy-substituted BDT, or dithienosilole, respectively, were prepared for investigating their photovoltaic performance and photostability. After only two hours of simultaneous exposure to light and air, the main absorption peak of the polymer films containing BDT units blue-shifted and its intensity dramatically decreased. We demonstrated that the BDT unit underwent dramatic structural change under illumination in air by reacting with the oxygen molecules at the excited state, leading to the disruption of the main-chain conjugation of the polymer. As a result, the color of the alkyl-BDT based polymer film permanently changed from deep blue to light yellow. In contrast, the dithienosilole based polymer was quite stable when treated under the same condition with negligible change in the absorption spectrum.

The synthesis and characterization of new heterofluorene derivatives based on germanium are described. These germafluorene monomers have been polymerized with different aromatic comonomers. The resulting homopolymers and alternating copolymers have been characterized by size exclusion chromatography, thermal analyses (TGA and DSC), UV-vis-NIR absorption spectroscopy, X-ray diffraction, and cyclic voltammetry. These homopolymers and copolymers are air-stable and present bandgaps ranging from 3.0 to 1.6 eV. Some copolymers were tested in field-effect transistors (FETs) and bulk heterojunction photovoltaic cells (PCs). Best results in FETs were obtained with poly[2,7-(9,9-di-n-butylgermafluorene)-alt 3,6-bis(thiophen-5-yl)-2,5-dioctylpyrrolo[3,4-]pyrrole-1,4-dione], which shows a hole mobility up to 0.04 cm2 (V 3 s)-1 with an Ion/Ioff ratio of 1.0_106. For photovoltaic applications, the best results were obtained with poly[2,7-(9,9-di-n-octylgermafluorene)-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] with a power conversion efficiency (PCE) of 2.8%.

We investigated the effect of solvents on the morphology, charge transport and device performance of 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 (PC 70BM) based solar cells. To carry out this investigation, chloroform and 1,2-dichlorobenzene were chosen as good solvents of the two compounds. Films prepared with chloroform exhibit larger domains than those prepared with 1,2-dichlorobenzene and their size increases with the amount of PC 70BM. Fine tuning of the domain size was realized by using a solvent of mixed chloroform and 1,2-dichlorobenzene. At a mixing ratio of 50%:50%, a power conversion efficiency of 6.1% was achieved on PCDTBT:PC 70BM (1:3) devices with an active area of 1 cm 2, under air mass 1.5 global (AM 1.5 G) irradiation at 100 mW/cm 2. © 2011 Published by Elsevier B.V. All rights reserved.

Polymer-fullerene bulk heterojunction (BHJ) solar cells have gained much attention in the past few years due to their potential as a low cost photovoltaic technology. The state-of-the-art power conversion efficiency (PCE) has been improved to 7% regime by the recent development of thieno[3,4-b] thiophene based low-band-gap polymers. This paper reports a new low-band-gap polymer with alternating thieno[3,4-b]thiophene and benzo[1,2-b:4,5-b′] dithiophene units for applications in BHJ solar cells. By optimizing the nano-scale morphology with DIO (1,8-diiodooctane) additive, the PCE of BHJ solar cells based on this new polymer has been improved dramatically from 1.4% to 4.8%. The correlation between photovoltaic performance and film morphology has been established for this new polymer/fullerene system. © 2011 Elsevier B.V. All rights reserved.

Incremental increase in dimethyl sulfoxide (or dimethyl formamide) in ortho-dichlorobenzene solution of poly [N -heptadecanyl-2,7-carbazole-alt-5,5- (4′, 7′ -di-2-thienyl- 2′, 1′, 3′ -benzothiadiazole)] (PCDTBT) gradually reduces the polymer-solvent interaction, the attraction forces between polymer chains become more dominant, and the polymer chains adopt a tight and contracted conformation with more interchain interactions, resulting in a progressive aggregation in both solutions and films. This was used to fine tune the morphology of PCDTBT/ PC71 BM based solar cells, leading to improved domain structure and hole mobility in the active layer, and significantly improved photovoltaic performance. The power conversion efficiency increased from 6.0% to 7.1% on devices with an active area of 1.0 cm2. © 2011 Crown.

The photovoltaic response of symmetric sandwich polymer cells based on poly[5-(2′-ethylhexyloxy)-2-methoxy-1,4-phenylene vinylene] (MEH-PPV) and MEH-PPV:fullerene blends has been investigated. Identical, semitransparent gold, silver, aluminum, and calcium are used as top and bottom electrodes. Most of the nominally symmetric sandwich cells exhibit pronounced photovoltaic (PV) response. The PV parameters are strongly dependent on the direction of illumination, the active layer thickness, and the evaporation rate of top electrode. Open-circuit voltage as high as 0.7 V has been measured in silver/MEH-PPV/silver cells. The addition of fullerene leads to reduced open-circuit voltage and higher short-circuit current. The photovoltaic response observed in these nominally symmetric sandwich cells is attributed to their different top and bottom electrode interfaces.

We combined experimental and computational approaches to tune the thickness of the films in poly(N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT)-based organic solar cells to maximize the solar absorption by the active layer. High power-conversion efficiencies of 5.2% and 5.7% were obtained on PCDTBT-based solar cells when using [6,6]-phenyl C61-butyric acid methyl ester (PC60BM) and [6,6]-phenyl C71-butyric acid methyl ester (PC70BM) as the electron acceptor, respectively. The cells are designed to have an active area of 1.0 cm2, which is among the largest organic solar cells in the literature, while maintaining a low series resistance of 5 Ω cm2.

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.

Organic solar cells based on interpenetrated network of conjugated polymer as donor and fullerene derivative as acceptor materials have a great potential for improvement of the efficiency. We fabricated a device based on a composite of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) and [6,6]-phenyl C60 butyric acid methyl ester (PCBM). Surface treatment, insertion of interfacial layers, and improvement of the morphology of the active layer significantly increase the photovoltaic performances of the structure. We obtained an open circuit voltage of 0.87 V and short circuit current density of -8.4 mA/cm2 under 100 mW/cm2 AM 1.5 solar simulator illumination, yielding a 2.9 % power conversion efficiency. Two others fullerene derivatives were synthesized in order to get a stronger acceptor. The electrical and optical properties of devices made with MEH-PPV and these acceptors are investigated.

The electromagnetic field distribution inside multilayer organic solar cells composed of interpenetrated networks of conjugated polymers is calculated. By enhancing the electromagnetic field in the photoactive region, an increase of the photovoltaic efficiency is expected.

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Two new soluble alternating alkyl-substituted benzo[1,2-b:4,5-b′] dithiophene and ketone-substituted thieno[3,4-b]thiophene copolymers were synthesized and characterized. We found that grafting 3-butyloctyl side chains to the benzo[1,2-b:4,5-b′]dithiophene unit at C4 and C8 afforded the resulting polymer (P1) a high hole mobility (∼10-2 cm2 Vs-1) and a low-lying HOMO energy level (5.22 eV). Preliminary experiments in bulk heterojunction solar cells using P1 as the electron donor demonstrated a high power conversion efficiency of 4.8% even with PC 61BM as the electron acceptor. The introduction of an electron-withdrawing fluorine atom into the thieno[3,4-b]thiophene unit at the C3 position (P2) lowers the HOMO energy level and consequently improves the open circuit voltage from 0.78 to 0.86 V. These values are about 0.1 V higher than those reported for their analogues based on alkoxy-substituted benzo[1,2-b:4,5-b′]dithiophene. This work demonstrates that the replacement of the alkoxy chains on the benzo[1,2-b:4,5-b′]dithiophene unit with less electron-donating alkyl chains is able to lower the HOMO energy levels of this class of polymers without increasing their band gap energy. © 2011 The Royal Society of Chemistry.

New oligofluorene modified C60 derivatives were designed and synthesized viarhodium complex catalyzed direct coupling between C60 and oligofluorene boronic acids in H2O/1,2-dichlorobenzene (1 : 4). The product was first purified by silica gel column chromatography and then further purified by semipreparative HPLC equipped with a Buckyprep column using toluene as an eluent. The strong deep-blue fluorescence of the oligofluorene bridge was completely quenched after end-capped with C60, indicating an efficient energy and/or charge transfer between the π-conjugated bridge and the C60 cages. Cyclic voltammetric measurements show that the HOMO and LUMO energy levels of the synthesized C60 derivatives are similar to those of widely used PC61BM. This means that the energy levels of the C60 derivatives mainly depend on the π electron system of the C60 cage. However, the substituents have huge impacts on the other physical properties of the resulting C60 derivatives, such as solubility, crystallinity, and electron mobility.

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We present the photovoltaic measurements of planar photovoltaic cells with extremely large interelectrode spacing based on either pure polymers or polymer∕fullerene blends. The planar configuration allows for both uniform and site-selective illuminations. As expected, cells with identical electrodes do not exhibit any photovoltaic action under uniform illumination. On the other hand, open-circuit voltage (VOC) greater than 1V has been observed in pure polymer cells with dissimilar gold∕calcium electrodes, which decreases when calcium is replaced with aluminum or when a fullerene derivative is added. In addition, all asymmetric cells exhibit photovoltaic action when the illumination is only applied to the anode half, the cathode, or the middle section of the cell. Our results provide unambiguous support to the metal∕insulator∕metal interpretation of polymer photovoltaic response.