Serge Beaupré

Bulk heterojunction solar cells using thieno[3,4-c]pyrrole-4,6-dione and dithieno[3,2-b:2',3'-d]silole copolymer with a power conversion efficiency of 7.3%.

A new alternating copolymer of dithienosilole and thienopyrrole-4,6-dione (PDTSTPD) possesses both a low optical bandgap (1.73 eV) and a deep highest occupied molecular orbital energy level (5.57 eV). The introduction of branched alkyl chains to the dithienosilole unit was found to be critical for the improvement of the polymer solubility. When blended with PC(71)BM, PDTSTPD exhibited a power conversion efficiency of 7.3% on the photovoltaic devices with an active area of 1 cm(2).

A Thieno[3,4-c]pyrrole-4,6-dione-Based Copolymer for Efficient Solar Cells

A new low-band-gap thieno[3,4-c]pyrrole-4,6-dione-based copolymer, PBDTTPD, has been designed and synthesized. PBDTTPD is soluble in chloroform or o-dichlorobenzene upon heating and shows a broad absorption in the visible region. The HOMO and LUMO energy levels were estimated to be at -5.56 and -3.75 eV, respectively. These electrochemical measurements fit well with an optical bandgap of 1.8 eV. When blended with PC(71)BM, this polymer demonstrated a power conversion efficiency of 5.5% in a bulk-heterojunction photovoltaic device having an active area of 1.0 cm(2).

Solar‐Energy Production and Energy‐Efficient Lighting: Photovoltaic Devices and White‐Light‐Emitting Diodes Using Poly(2,7‐fluorene), Poly(2,7‐carbazole), and Poly(2,7‐dibenzosilole) Derivatives

World energy needs grow each year. To address global warming and climate changes the search for renewable energy sources with limited greenhouse gas emissions and the development of energy-efficient lighting devices are underway. This Review reports recent progress made in the synthesis and characterization of conjugated polymers based on bridged phenylenes, namely, poly(2,7-fluorene)s, poly(2,7-carbazole)s, and poly(2,7-dibenzosilole)s, for applications in solar cells and white-light-emitting diodes. The main strategies and remaining challenges in the development of reliable and low-cost renewable sources of energy and energy-saving lighting devices are discussed.

Highly efficient organic solar cells based on a poly(2,7-carbazole) derivative

We have studied the utilization of PCDTBT, an alternating poly(2,7-carbazole) derivative, in organic bulk heterojunction solar cells. The effect of polymer molecular weight, PCDTBT:[60]PCBM ratio, and active layer thickness on the device performance is reported. The best performance was obtained when the number-average molecular weights (Mn) are around 20 kDa with a polydispersity index around 2.2. Both PCDTBT:[60]PCBM ratio and active layer thickness affect the light absorption and the charge transport properties. By optimizing these two parameters, power conversion efficiency (PCE) up to 4.35% was reached under calibrated AM1.5G illumination of 100 mW cm−2. When blended with [70]PCBM, PCDTBT exhibited a PCE up to 4.6%.

A Thermally Stable Semiconducting Polymer

A bs or pt io n RT 120 170 200 250 300 350 400 Early research on polymer electronic devices successfully demonstrated function and performance adequate for specific applications. As a result, the performance of devices fabricated from semiconducting polymers has improved to the point where ‘‘plastic’’ electronics are now expected to develop into a significant industry with a large market opportunity. However, the limited stability of polymer-based devices continues to hinder the path toward commercialization. Because stability in air is critical to the commercialization of polymer electronic devices, discussions concerning the stability of semiconducting polymers have focused on degradation caused by reaction with oxygen and water vapor. Conjugated polymers are, however, generally believed to be incapable of withstanding high temperatures (i.e., temperatures well above the glasstransition temperature, Tg), [6,7] thus, stability at high temperatures has received less attention. The availability of semiconducting polymers that can survive exposure to elevated temperatures would open a variety of new possibilities. For example, since inorganic electronic devices typically require process steps that must be carried out at high temperature (often over 300 8C), semiconducting polymers capable of withstanding high temperatures will enable the fabrication of novel organic–inorganic hybrid devices. Here, we report the remarkable stability of the poly(2,7carbazole) derivative, poly[N-900-hepta-decanyl-2,7-carbazole-alt5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)], (PCDTBT; see the inset of Fig. 1a). Prior to this report, there was no known example of a semiconducting polymer that is both stable in air at (and above) room temperature and capable of withstanding high temperatures for extended periods of time. PCDTBT is one of a relatively large class of ‘‘donor–acceptor’’ polycarbazole co-polymers. Recently, polymer bulkheterojuction solar cells fabricated with phase-separated blends of PCDTBT and PC71BM were demonstrated with internal quantum efficiency approaching 100%, power conversion efficiency of 17% in response to monochromatic radiation within the absorption band, and power conversion efficiency of 6.1% in response to solar radiation. To investigate the stability of PCDTBT, we have carried out spectroscopic studies on PCDTBT thin films and transport studies using the field-effect transistor (FET) architecture with PCDTBTas the semiconductor material in the channel. Figure 1 shows UV–visable (UV–vis) absorption spectra of PCDTBT thin films annealed for 15 minutes at various temperatures in air (Fig. 1a) and under N2 atmosphere (Fig. 1b). In air, the p–p* absorption spectrum is not affected after exposure to temperatures up to 150 8C. Under N2 atmosphere (Fig 1b), the electronic band structure of PCDTBT is stable after exposure to temperatures as high as 350 8C.

Polycarbazoles for plastic electronics

This Review covers recent progress made in the synthesis of carbazole-based monomers and polymers and their applications in plastic electronics. That includes the first photoactive carbazole-containing polymer, namely PVK, conjugated poly(3,6-carbazole)s, and finally the latest developments in poly(2,7-carbazole) derivatives. We will mainly discuss photovoltaic cell applications because of the impressive performances that have been obtained in the past couple of years. Semi-ladder poly(indolo[3,2-b]carbazole)s that have recently shown interesting features will also be presented.

Fluorene‐Based Copolymers for Red‐Light‐Emitting Diodes

The syntheses of new fluorene-based π-conjugated copolymers; namely, poly((5,5″-(3′,4′-dihexyl-2,2′;5′,2″-terthiophene 1′,1′-dioxide))-alt-2,7-(9,9-dihexylfluorene)) (PFTORT), poly((5,5″″-(3″,4″-dihexyl-2,2′:5′,2′:5″,2‴:5‴,2″″-quinquethiophene 1″,1″-dioxide))-alt-2,7-(9,9-dihexylfluorene)) (PFTTORTT), and poly((5,5-E-α-(2-thienyl)methylene)-2-thiopheneacetonitrile)-alt-2,7-(9,9-dihexylfluorene)) (PFTCNVT), are reported. In the solid state, PFTORT and PFTCNVT present red–orange emission (with a maximum at 610 nm) while PFTTORTT shows a red emission with a maximum at 666 nm. In all cases, electrochemical measurements have revealed p- and n-dopable copolymers. All these copolymers have been successfully tested in simple light-emitting diodes and show promising results for orange- and red-light-emitting devices.

Highly efficient polycarbazole-based organic photovoltaic devices

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.

PCDTBT: en route for low cost plastic solar cells

Since its inception in 1995, significant advances in the field of bulk heterojunction (BHJ) solar cells have been made and polymeric semiconductors are now considered to be one of the most promising ways to lower the cost of the energy generated by solar cells. Power conversion efficiencies (PCEs) are now reaching the threshold values for commercialisation (9.2% for single-layer BHJ and 10.6% for tandem devices). PCDTBT, a carbazole-based copolymer, is among the most efficient, stable and low-cost materials for BHJ solar cells with a high open-circuit voltage (Voc ∼ 0.90 V), power conversion efficiency of 7.5% and estimated lifetime of 7 years. PCDTBT surpasses the performance of P3HT (the most studied polymeric material until now) and is now considered as one of the new benchmarks for the development of highly efficient BHJ solar cells.

Blue light-emitting devices from new conjugated poly(N-substituted-2,7-carbazole) derivatives

Light-emitting diodes derived from a new class of conjugated polymers, well-defined poly(N-substituted-2,7-carbazole) derivatives, are reported. Excimer-free electroluminescence in the blue range (424–432 nm) was observed. Good luminance (372 cd/m2 at 10 V) was reached in a device containing poly[N-(2-ethylhexyl)-2,7-carbazole] as the emitting material with indium tin oxide and Al as the electrodes. This high luminance value was achieved by adding ultrathin LiF layers next to the electrodes, and by using hole and electron transport molecules such as N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine and 2-(4-biphenylyl)-5(4-tert-butylphenyl)-1,3,4-oxadiazole.