Conjugated polymer chains have many degrees of conformational freedom and interact weakly with each other, resulting in complex microstructures in the solid state. Understanding charge transport in such systems, which have amorphous and ordered phases exhibiting varying degrees of order, has proved difficult owing to the contribution of electronic processes at various length scales. The growing technological appeal of these semiconductors makes such fundamental knowledge extremely important for materials and process design. We propose a unified model of how charge carriers travel in conjugated polymer films. We show that in high-molecular-weight semiconducting polymers the limiting charge transport step is trapping caused by lattice disorder, and that short-range intermolecular aggregation is sufficient for efficient long-range charge transport. This generalization explains the seemingly contradicting high performance of recently reported, poorly ordered polymers and suggests molecular design strategies to further improve the performance of future generations of organic electronic materials.

http://absimage.aps.org/image/MAR14/MWS_MAR14-2013-020288.pdf

A general relationship between disorder, aggregation and charge transport in conjugated polymers

Optical sensor development has been pursued over past 25 years, which has also seen development of novel chemistries, materials, sensor designs and optical instrumentation. In addition, novel signal and data processing techniques have been adopted in the sensor development. New techniques and materials in chemical and biological sensing have set further stages of advanced research. One of the most recent technological advances in this area has been the development of optical nanosensors, which are sensors with dimensions on the nanometer scale. Nanosensors of various types (e.g. optical, electrochemical) have been published in the literature over the past decade. Optical nanosensors, like the larger and macro scale sensors, can be either chemical or biological, depending on the type of probe used. Both types of sensors have been studied to provide a reliable method of monitoring various chemicals in microscopic environments and have been used to detect molecules within single cells. The field of nanosensing is relatively new and reports in the literature presenting any problems associated with such a scale of analysis are sparse. This paper will briefly review some of the current developments in the field of optical nanosensors.

Optical sensors

Organic semiconductors require an energetic offset in order to photogenerate free charge carriers efficiently, owing to their inability to effectively screen charges. This is vitally important in order to achieve high power conversion efficiencies in organic solar cells. Early heterojunction-based solar cells were limited to relatively modest efficiencies (<4%) owing to limitations such as poor exciton dissociation, limited photon harvesting, and high recombination losses. The development of the bulk heterojunction (BHJ) has significantly overcome these issues, resulting in dramatic improvements in organic photovoltaic performance, now exceeding 18% power conversion efficiencies. Here, the design and engineering strategies used to develop the optimal bulk heterojunction for solar-cell, photodetector, and photocatalytic applications are discussed. Additionally, the thermodynamic driving forces in the creation and stability of the bulk heterojunction are presented, along with underlying photophysics in these blends. Finally, new opportunities to apply the knowledge accrued from BHJ solar cells to generate free charges for use in promising new applications are discussed.

/pdf/the-bulk-heterojunction-in-organic-photovoltaic-120l9bpof7.pdf

The Bulk Heterojunction in Organic Photovoltaic, Photodetector, and Photocatalytic Applications.

Visible to Near-Infrared Photodetection Based on Ternary Organic Heterojunctions

Future lightweight, flexible, and wearable electronics will employ visible-light-communication schemes to interact within indoor environments. Organic photodiodes are particularly well suited for such technologies as they enable chemically tailored optoelectronic performance and fabrication by printing techniques on thin and flexible substrates. However, previous methods have failed to address versatile functionality regarding wavelength selectivity without increasing fabrication complexity. This work introduces a general solution for printing wavelength-selective bulk-heterojunction photodetectors through engineering of the ink formulation. Nonfullerene acceptors are incorporated in a transparent polymer donor matrix to narrow and tune the response in the visible range without optical filters or light-management techniques. This approach effectively decouples the optical response from the viscoelastic ink properties, simplifying process development. A thorough morphological and spectroscopic investigation finds excellent charge-carrier dynamics enabling state-of-the-art responsivities >102 mA W-1 and cutoff frequencies >1.5 MHz. Finally, the color selectivity and high performance are demonstrated in a filterless visible-light-communication system capable of demultiplexing intermixed optical signals.

/pdf/color-selective-printed-organic-photodiodes-for-filterless-32nfsseaz7.pdf

Color-Selective Printed Organic Photodiodes for Filterless Multichannel Visible Light Communication

Organic photodiodes (OPDs) are set to enhance traditional optical detection technologies and open new fields of applications, through the addition of functionalities such as wavelength tunability, mechanical flexibility, light-weight or transparency. This, in combination with printing and coating technology will contribute to the development of cost-effective production methods for optical detection systems. In this review, we compile the current progress in the development of OPDs fabricated with the help of industrial relevant coating and printing techniques. We review their working principle and their figures-of-merit (FOM) highlighting the top device performances through a comparison of material systems and processing approaches. We place particular emphasis in discussing methodologies, processing steps and architectural design that lead to improved FOM. Finally, we survey the current applications of OPDs in which printing technology have enabled technological developments while discussing future trends and needs for improvement.

/pdf/organic-photodiodes-printing-coating-benchmarks-and-k958c21mtq.pdf

Organic photodiodes: printing, coating, benchmarks, and applications

Digitally printed organic photodiodes (OPDs) are of great interest for the cost-efficient additive manufacturing of single and multidevice detection systems with full freedom of design. Recently reported high-performance non-fullerene acceptors (NFAs) can address the crucial demands of future applications in terms of high operational speed, tunable spectral response, and device stability. Here, we present the first demonstration of inkjet and aerosol-jet printed OPDs based on the high-performance NFA, IDTBR, in combination with poly(3-hexylthiophene), exhibiting a spectral response up to the near-infrared (NIR) region. These digitally printed devices reach record responsivities up to 300 mA/W in the visible and NIR spectrum, competing with current commercially available technologies based on Si. Furthermore, their fast dynamic response with cutoff frequencies surpassing 2 MHz outperforms most of the state-of-the-art OPDs. The successful process translation from spin-coating to printing is highlighted by t...

Non-Fullerene-Based Printed Organic Photodiodes with High Responsivity and Megahertz Detection Speed

Organic photodiodes (OPDs) are optical sensors combining high performance, lightweight mechanical flexibility, and processability from solution. Their fabrication by industrial printing techniques opens a wide range of innovative applications for emerging fields in sensing and the Internet of Things. They typically consist of printed multilayers with functionalities to absorb light, to extract charges, or to reduce detection noise. However, the printing of such device architecture poses a challenge as the deposition of a material can lead to disruption of film morphology or intermixing of materials if its solvent interacts with the previously deposited layer. This work proposes a process to print multilayers from the same solvent system utilizing the aerosol-jet technique. By fine adjustment of the aerosol properties through the tube temperature (TTube), the drying time of poly(3-hexylthiophene-2,5-diyl) (P3HT) printed layers is significantly reduced. This allows its deposition onto a P3HT-based bulk-heterojunction (BHJ) without negatively affecting its performance. The additional printed P3HT layer, spatially extends the donor region of the BHJ, providing ideal hole extraction and simultaneous noise reduction by the blocking of injected electrons. This donor blocking layer (DBL) yields a noise reduction of two orders of magnitude in OPDs operated under −2 V reverse bias.

/pdf/aerosol-jet-printed-donor-blocking-layer-for-organic-39egka7xey.pdf

Mervin Seiberlich

Papers

Color-Selective Printed Organic Photodiodes for Filterless Multichannel Visible Light Communication

Organic photodiodes: printing, coating, benchmarks, and applications

Non-Fullerene-Based Printed Organic Photodiodes with High Responsivity and Megahertz Detection Speed

Aerosol‐Jet‐Printed Donor‐Blocking Layer for Organic Photodiodes

Inkjet-Printed Tin Oxide Hole-Blocking Layers for Organic Photodiodes