• Energy Research

Accurate characterization and reporting of organic photovoltaic (OPV) device performance reniains one of the important challenges in the field. The large spread among the efficiencies of devices with the same structure reported by different groups is significantly caused by different procedures and equipment used during testing. The presented article addresses this issue by offering a new method of device testing using "suitcase sample" approach combined with outdoor testing that limits the diversity of the equipment, and a strict measurement protocol. A round robin outdoor characterization of roll-to-roll coated OPV cells and modules conducted among 46 laboratories worldwide is presented, where the samples and the testing equipment were integrated in a compact suitcase that served both as a sample transportation tool and as a holder and test equipment during testing. In addition, an internet based coordination was used via plasticphotovoltaics.org that allowed fast and efficient communication among participants and provided a controlled reporting format for the results that eased the analysis of the data. The reported deviations among the laboratories were limited to 5% when compared to the Si reference device integrated in the suitcase and were up to 8% when calculated using the local irradiance data. Therefore, this method offers a fast, cheap and efficient tool for sample sharing and testing that allows conducting outdoor measurements of OPV devices in a reproducible manner. (C) 2014 Elsevier B.V. All rights reserved.

Herein, the design and fabrication of a smart electrochromic supercapacitor using Au mesh and polyaniline (PANI) electrodes is reported. The Au mesh is obtained through the crackle templating method, whereas PANI is brought in by electrodeposition. The device exhibits a high capacitance of ≈15 mF cm−2 with good charge–discharge cycling stability. What is attractive about this device is that it can switch its color rapidly to yellow, green, or blue, depending on the operable voltage window that should serve to indicate the level of energy stored in the supercapacitor, visually.

AbstractIn the quest for indium‐tin oxide (ITO)‐free photovoltaics and for building integrated as well as automobile roof applications, novel transparent electrodes for both front and back electrodes are required. Here we report the fabrication and integration of submicrometer transparent silver (Ag) and gold (Au) metal network electrodes, which are invisible to the naked eye, in organic photovoltaic devices. We exploit the idea of using the spontaneous cracking of a polymer layer as template to prepare the metal network. The main challenge is to apply the cracked template approach on top of soluble organic layers and to lift off the template without damaging the photoactive layer. We demonstrate that Ag or Au back electrodes can be fabricated maintaining a transmittance of 80 % for the whole visible range. These electrodes exhibit ultralow haze of approximately 5 % and an excellent figure of merit value. Moreover, the ITO‐free semitransparent polymer solar cell incorporating the Ag/Ag network electrodes exhibits 57 % transmittance above 650 nm.

Abstract Indoor light control using thermotropic materials is an active area of research. While active materials are available to switch transmittance with temperature, large area heaters with desired transparency are not easily affordable. In this paper, the fabrication of thermochromic devices using inexpensive Sn mesh electrodes (5 Ω/□, transmission, 80%) produced by crackle lithography with hydroxypropyl methyl cellulose (HPMC) as active material is reported. When laminated and coated on the inner surface of a PET window (8×8 cm2), the mesh served as a transparent heater to cause gelation in HPMC at ~40 °C to switch from water-clear transparency to paper-white opaqueness with 1 mm thickness of the active layer. The power consumption was only 0.2 W/cm2. Few drops of a color ink produced interesting effects in this smart window prototype.

AbstractA solution‐processed silver film is employed in the processing of top‐illuminated indium‐tin‐oxide (ITO)‐free polymer solar cells in single‐ and double‐junction (tandem) structures. The nontransparent silver film fully covers the substrate and serves as the bottom electrode whereas a PEDOT:PSS/Ag grid forms the semitransparent top electrode. All layers are roll‐coated/printed on a flexible substrate by using only two techniques: slot–die coating for up to 11 consecutive layers and flexo‐printing for the last Ag grid layer. The slot–die coated Ag film is compared to an evaporated Ag film in terms of surface morphological and topographical properties and to ITO in terms of flexibility. The slot–die coated Ag film demonstrates extremely low roughness (a root‐mean‐square roughness of 3 nm was measured over 240×320 μm2 area), is highly conductive (<1 Ω/□), highly flexible, and cost‐effective in comparison to other reported metal films applied in polymer solar cells. Such properties result in high fill factors exceeding 50 % in both single and tandem structures on large‐area devices (1 cm2) and the corresponding efficiencies exceed 2 %.

AbstractAs solar cell modules are becoming larger, it is important to pay attention to defects originating from the fabrication process and degradation during operation in the ambient. In this article, a simple method of using computer screen display as a light source to map the photoresponse of the solar cells, is reported. The method requires only a conventional computer loaded with a software code that enables a light spot of defined size to raster scan across the cell area as the photogenerated voltage is read out by a voltmeter using a USB connection. Screen‐display‐induced photoresponse (SDIP) mapping is an enabling technique to reveal the defective regions in the active layer as well as at the electrode interface, which, in many instances, cannot be deciphered simply by visual examination. Spectral response mapping by using light spots of different colors is also possible.

AbstractFlexible, semitransparent and robust heating arrays have been designed by grayscale printing as ready‐to‐use devices for point‐of‐care application. A perforated Ag mesh is first fabricated with tunable features by controllably varying the toner grayscale value during laser printer on PET. The resistance could be varied between 1 to 2 Ω by tuning the Ag fill factor from 50 to 70 %. The Ag/PET heater based on joule heating is able to attain highly stable temperatures upto ∼135 °C maintained over long hours. Since temperature is directly related to resistance, this provides a fine temperature knob without any cumbersome processing steps. The merit of design allows individual heating elements to attain stable temperatures at low voltages (∼1.5 V) without any interference from neighboring heaters of the array, thus resulting in a thermal library. A laptop USB with 5.1 V output is able to power the thermal library for temperatures in the range of 30–60 °C, useful in many practical applications. It is a multipurpose disposable chip for in‐situ transmission microscopy that can be utilized for bioassay and point‐of‐care diagnostics, as demonstrated in the study.

Supercapacitors have emerged to fill the gap between batteries and capacitors. The electrodes comprising a high surface area are utilized to fabricate the supercapacitors. However, the processes involved to fabricate electrodes are often strenuous and time‐consuming. Herein, the fabrication of high‐performance supercapacitors using frosted glass as a template to grow electrodes is reported. The frosted substrates can host much higher ions owing to the numerous surface features arising from micro‐ and nano‐level roughnesses, resulting in one order higher capacitance than the plain surface. Electrodepositing MnO2 nanostructures on the frosted surface further increases the capacitance and attains the highest value of 11 mF cm−2 at 300 min of electrodeposition, which is 6.5 times higher than the electrodes without MnO2. The stacked supercapacitors are made using polyvinyl alcohol/H2SO4 gel electrolyte, and the devices exhibit superior electrochemical properties such as high scan rate stability (100 V s−1), high cut‐off frequency (333 Hz), low iR drop, high cyclic stability (93% capacitance retention after 10 000 cycles), and low self‐discharge. The roughened nature of the frosted glass can be imprinted onto the surface of polydimethylsiloxane substrate to fabricate flexible and stretchable supercapacitors. The present work can pave the way for facile and low‐cost fabrication of supercapacitor electrodes.