The printed electronics industry offers a paradigm change in manufacturing, cost and environmental impact when compared to the conventional semiconductor industry. Printed electronic devices are expected to be mass-produced from less-energy-demanding processes over large areas and on flexible substrates with techniques that closely resemble the well-known mass production of printed media on paper. Organic light-emitting diodes (OLEDs) offer great versatility in the design of application-specific light sources; yet examples of OLEDs fabricated on exotic substrates that differ from glass and plastic are still scarce. In this talk we will present recent examples of OLEDs fabricated on unconventional substrates, including nanocellulose and shape memory polymers.
Organic photovoltaics (OPV) can lead to a low cost and short energy payback time alternative to existing photovoltaic technologies. However, to fulfill this promise, power conversion efficiencies must be improved and simultaneously the architecture of the devices and their processing steps need to be further simplified. In the most efficient devices to date, the functions of photocurrent generation, and hole/electron collection are achieved in different layers adding complexity to the device fabrication. In this talk, we present a novel approach that yields devices in which all these functions are combined in a single layer.
Specifically, we report on bulk heterojunction devices in which amine-containing polymers are first mixed in the solution together with the donor and acceptor materials that form the active layer. A single-layer coating yields a self-forming bottom electron-collection layer comprised of the amine-containing polymer (e.g. PEIE). Hole-collection is achieved by subsequent immersion of this single layer in a solution of a polyoxometalate (e.g. phosphomolybdic acid (PMA)) leading to an electrically p-doped region formed by the diffusion of the dopant molecules into the bulk. The depth of this doped region can be controlled with values up to tens of nm by varying the immersion time. Devices with a single 500 nm-thick active layer of P3HT:ICBA processed using this method yield power conversion efficiency (PCE) values of 4.8 ± 0.3% at 1 sun and demonstrate a performance level superior to that of benchmark three-layer devices with separate layers of PEIE/P3HT:ICBA/MoOx (4.1 ± 0.4%). Devices remain stable after shelf lifetime experiments carried-out at 60 °C over 280 h.
Although the detection of photons is ubiquitous, man-made photon detectors still limits the effectiveness of applications such as light/laser detection, photography, astronomy, quantum information science, medical imaging, microscopy, communications, and others. The performance of the technologically most advanced detectors based on CMOS semiconductor technology has improved during the last decades but at the detriment of increased complexity, higher cost, limited portability and compactness, and limited area. On the other hand, nature has produced a relatively simple detector with remarkable properties: the human eye. The exploration of new paradigms in photon detection using new material platforms might therefore provide a path to further challenge the frontiers of applications enabled by light.
In this talk, we will report on the realization of solution-processed organic semiconductor visible spectrum photodetectors with a high specific detectivity above 1014 Jones, at least an order of magnitude larger than values found in photodiodes based on silicon. These detectors demonstrate a sub-pA current under reverse bias in the dark, making them suitable for detecting very low levels of light. The small dark current under reverse bias allows the characterization of these devices over 9 orders of magnitude of increasing light irradiance. The detectors are based on the device structure: tin-doped indium oxide / ethoxylated polyethylenimine / poly(3-hexylthiophene) : indene C60 bisadduct / molybdenum oxide / silver and present a path toward fabrication on flexible substrates. We will show that these detectors can operate over a large dynamic range in the self-powered photovoltaic mode where the light produces a photovoltage that can be measured directly without any external bias source. We believe that large-area flexible photodetectors with detectivity values comparable to or better than those displayed by silicon-based photodiodes will enable a wide variety of applications from the detection of radiation to non-planar imaging arrays.