Paul J. Glatkowski

Organic solar cells with carbon nanotubes replacing In2O3:Sn as the transparent electrode

We report two viable organic excitonic solar cell structures where the conventional In2O3:Sn (ITO) hole-collecting electrode was replaced by a thin single-walled carbon nanotube layer. The first structure includes poly(3,4-ethylenedioxythiophene) (PEDOT) and gave a nonoptimized device efficiency of 1.5%. The second did not use PEDOT as a hole selective contact and had an efficiency of 0.47%. The strong rectifying behavior of the device shows that nanotubes are selective for holes and are not efficient recombination sites. The reported excitonic solar cell, produced without ITO and PEDOT, is an important step towards a fully printable solar cell.

Single-wall carbon nanotube networks as a transparent back contact in CdTe solar cells

Single-wall carbon nanotube (SWCNT) networks form a highly transparent and electrically conductive thin film that can be used to replace traditional transparent conducting oxides (TCOs) in a variety of applications. Here, the authors demonstrate their use as a transparent back contact in a near-infrared (NIR) transparent CdTe solar cell. SWCNT networks are hole-selective conductors and have a significantly greater NIR transparency than TCOs—qualities which could both make them very useful in tandem thin-film solar cells. SWCNT networks can be incorporated into single-junction CdTe devices and in CdTe top cells for mechanically stacked thin-film tandem devices, as described here. The best device efficiency using SWCNTs in the back contact was 12.4%, with 40%–50% transmission between 800 and 1500nm.

Anisotropy of the linear and third‐order nonlinear optical properties of a stretch‐oriented polymer film of poly‐[2, 5‐dimethoxy paraphenylenevinylene]

Large linear refractive index birefringence, strong dichroic behavior, and highly anisotropic χ(3) have been observed for a uniaxially oriented poly (2, 5‐dimethoxy paraphenylene vinylene) film. A subpicosecond time‐resolved degenerate four‐wave mixing study reveals an unusual behavior. Along the draw direction χ(3) is complex with a negative real part and has a response time that is longer than the optical pulse resolution. In contrast, χ(3) along the transverse direction is largely real and positive. Its response time is much faster, and is limited by the laser pulse width of ∼400 fs.

Application of Single-Wall Carbon Nanotubes as Transparent Electrodes in Cu(In,Ga)Se2-Based Solar Cells

We present a new thin-film solar cell structure in which the traditional transparent conductive oxide electrode (ZnO) is replaced by a transparent conductive coating consisting of a network of bundled single-wall carbon nanotubes. Optical transmission properties of these coatings are presented in relation to their electrical properties (sheet resistance), along with preliminary solar cell results from devices made using CuIn1-xGaxSe2 thin-film absorber materials. Achieving an energy conversion efficiency of >12% and a quantum efficiency of ~80% demonstrate the feasibility of the concept. A discussion of the device structures will be presented considering the physical properties of the new electrodes comparing current-voltage results from the new solar cell structure and those from standard ZnO/CdS/Cu(In,Ga)Se2/Mo solar cells

Mid-IR tapered chalcogenide fiber optic attenuated total reflectance sensors for monitoring epoxy resin chemistry

The development of new infrared transmitting optical fibers with low optical losses, sufficient mechanical strength, and temperature range to meet the demanding conditions of many process environments -- and the availability of improved, ruggedized low-cost FTIR spectrometers -- have made in situ FTIR measurements possible. This paper discusses the development of a mid-IR tapered infrared transmitting optical fiber for monitoring the cure of epoxy resins.

Carbon nanotube-composite wafer bonding for ultra-high efficiency III–V multijunction solar cells

Device-wafer bonding provides a platform for the implementation of ultra-high-efficiency multijunction solar cell designs, by allowing optimal subcell bandgap combinations to be attained while using only high-quality materials lattice-matched to their growth substrates. One promising new method for achieving wafer bonding is to use carbon nanotube composite thin films as the bonding agent between subcells grown on dissimilar substrates. In this paper we present the first demonstration of CNT-composite bonding of III–V materials, and evaluate its suitability for solar-cell integration in terms of optical transparency, electrical conductivity, bond uniformity and robustness, and bonded-device electrical performance. Another, relatively more mature method for device-wafer integration is that of direct semiconductor bonding technology. In order to provide a basis for comparison with CNT-bonding, we also summarize the latest achievements of the SBT solar cell development effort at Spectrolab.

In-situ characterization of resin chemistry with infrared transmitting optical fibers and infrared spectroscopy

The real-time in situ monitoring of the chemical states of epoxy and polyimide resins were investigated during cure using an embedded fiber optic sensor and a Fourier transform infrared spectrometer (FTIR). In this work a short length of sapphire fiber is used as the sensor for monitoring the cure of the epoxy, while for the polyimide resin, we use a chalcogenide fiber as the sensor. The cure of the epoxy resin/graphite fiber composite is monitored in an autoclave, while the cure of the polyimide resin/graphite fiber composite is monitored in a high temperature press. The sapphire sensor is connected to infrared transmitting zirconium fluoride optical fiber cables which penetrate the wall of the autoclave and interface to the FTIR spectrometer. The chalcogenide sensor connects to other chalcogenide fibers which act as a transmission link to the FTIR spectrometer. The results indicate that this equipment and sensors are suitable for monitoring the degree of cure of the laminates throughout the entire cure cycle.

Single-Wall Carbon Nanotubes as Transparent Electrodes for Photovoltaics

Transparent and electrically conductive coatings and films have a variety of uses in the fast-growing field of optoelectronic applications. Transparent electrodes typically include semiconductive metal oxides such as indium tin oxide (ITO), and conducting polymers such as poly(3,4-ethylenedioxythiophene), doped and stabilized with poly(styrenesulfonate) (PEDOT/PSS). In recent years, Eikos, Inc. has conceived and developed technologies to deliver novel alternatives using single-wall carbon nanotubes (SWNT). These technologies offer products having a broad range of conductivity, excellent transparency, neutral color tone, good adhesion, abrasion resistance as well as mechanical robustness. Additional benefits include ease of ambient processing and patterning capability. This paper reports our recent findings on achieving 2.6% and 1.4% efficiencies on nonoptimized organic photovoltaic cells employing SWNT as a transparent electrode

Applications of remote fiber optic spectroscopy using IR fibers and Fourier transform infrared spectrometers

The development of new infrared transmitting optical fibers with low optical losses, sufficient mechanical strength, and temperature range to meet the demanding conditions of many process environments; and the availability of improved, ruggedized low-cost FTIR spectrometers have made in situ FTIR measurements possible. This paper discusses the development of in situ fiber optic remote FTIR spectroscopy and its application to the characterization of thin polymer coatings on substrates and the development of evanescent wave in situ fiber optic remote FTIR spectroscopy and its application to assaying components of biological fluids.

In-situ fiber optic FTIR spectroscopy for coal liquefaction processes

The development of diagnostic instrumentation for monitoring coal liquefaction process streams is discussed. A sapphire optical fiber was used as an attenuated total reflectance (ATR) element in conjunction with Fourier transform infrared (FT-IR) spectrometry to probe harsh liquefaction process streams. ATR provides a short, reproducible pathlength which allows for the analysis of highly absorbing materials, such as liquid hydrocarbons, and the properties of sapphire are well suited for the analysis of high temperature and high pressure process streams. A test cell was constructed which allowed in-situ monitoring of coal liquefaction reactions at 400 degree(s)C and 3000 psig. The cell incorporated a sapphire optical fiber as an ATR sensing element which was coupled to an FT-IR spectrometer using zirconium fluoride fiber optic cables. The spectra provide qualitative information about the liquefaction process.