Richard R. Lunt

Michigan State University, Ист-Лансинг, Michigan, United States

Are you Richard R. Lunt?

Claim your profile

Publications (47)365.98 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Devices utilizing an entirely new class of earth abundant, inexpensive phosphorescent emitters based on metal halide nanoclusters are reported. Light-emitting diodes with tunable performance are demonstrated by varying cation substitution to these nanoclusters. Theoretical calculations provide insight about the nature of the phosphorescent emitting states, which involves a strong pseudo-Jahn-Teller distortion.
    No preview · Article · Nov 2015 · Advanced Materials
  • [Show abstract] [Hide abstract]
    ABSTRACT: A new series of organic salts with selective near-infrared (NIR) harvesting to 950 nm is reported, and anion selection and blending is demonstrated to allow for fine tuning of the open-circuit voltage. Extending photoresponse deeper into the NIR is a significant challenge facing small molecule organic photovoltaics, and recent demonstrations have been limited by open-circuit voltages much lower than the theoretical and practical limits. This work presents molecular design strategies that enable facile tuning of energy level alignment and open-circuit voltages in organic salt-based photovoltaics. Anions are also shown to have a strong influence on exciton diffusion length. These insights provide a clear route toward achieving high efficiency transparent and panchromatic photovoltaics, and open up design opportunities to rapidly tailor molecules for new donor-acceptor systems.
    No preview · Article · Oct 2015 · Advanced Energy Materials
  • [Show abstract] [Hide abstract]
    ABSTRACT: Building integrated photovoltaic (BIPV) systems are an emerging approach to reduce installation costs while supplementing building energy needs. However, the physical constraints of the building architecture often prevent photovoltaic systems from being installed at their optimal orientation. Recently, it was shown that thin film photovoltaics can be designed for improved angle-dependent responsivity at specific angles. In this study, the complex impact of angular dependency on overall power output is explored based on detailed hourly solar position, location, and flux data. These results demonstrate that reducing the angular roll-off dependence can enhance overall power outputs by 30% or more in fixed orientation configurations depending on the geographical location, orientation, and angle-dependent roll-off characteristics.
    No preview · Article · Jan 2015 · Solar Energy Materials and Solar Cells
  • Yimu Zhao · Garrett A. Meek · Benjamin G. Levine · Richard R. Lunt
    [Show abstract] [Hide abstract]
    ABSTRACT: A transparent luminescent solar concentrator that selectively harvests NIR photons is demonstrated. On page 606, R. R. Lunt and co-workers describe the photophysical and electronic properties of the luminophores, the impact of ligandhost control, and the optimization of the solar concentrator architectures to realize their potential for use in electronic displays, solar windows, and other glazing systems with high defect tolerances and processability.
    No preview · Article · Jul 2014 · Advanced Optical Materials
  • Yimu Zhao · Garrett A. Meek · Benjamin G. Levine · Richard R. Lunt
    [Show abstract] [Hide abstract]
    ABSTRACT: Near-infrared (NIR) harvesting transparent luminescent solar concentrators (TLSC) with non-tinted transparency are demonstrated by exploiting the excitonic nature of organic luminescent salts that provide perfectly tuned NIR-selective absorption and even deeper NIR emission. NIR TLSCs provide an entirely new route to more aesthetically pleasing light harvesting systems that can be widely deployed in energy scavenging windows and displays.
    No preview · Article · Jul 2014 · Advanced Optical Materials
  • [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate efficient zinc sulfide cathode window layers in thin-film organic photovoltaics enabled by n-type doping zinc sulfide (ZnS) with aluminum sulfide (Al2S3) directly through co-deposition. By optimizing the Al2S3 concentration, the power conversion efficiency is improved from 0.6% ± 0.2% in undoped ZnS window layer devices to 1.8% ± 0.1%, identical to control devices. The mechanism for this performance enhancement is shown to stem from the enhanced conductivity and interface energetics of ZnS upon n-type doping. This work expands the catalog of efficient, inorganic, non-toxic, cathode side window layers that could be effective in a range of thin-film photovoltaic technologies.
    No preview · Article · May 2014 · Journal of Applied Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: The electronic properties of colloidal quantum dots (QDs) are critically dependent on both QD size and surface chemistry. Modification of quantum confinement provides control of the QD bandgap, while ligand-induced surface dipoles present a hitherto-underutilized means of control over the absolute energy levels of QDs within electronic devices. Here we show that the energy levels of lead sulfide QDs, measured by ultraviolet photoelectron spectroscopy, shift by up to 0.9 eV between different chemical ligand treatments. The directions of these energy shifts match the results of atomistic density functional theory simulations and scale with the ligand dipole moment. Trends in the performance of photovoltaic devices employing ligand-modified QD films are consistent with the measured energy level shifts. These results identify surface-chemistry-mediated energy level shifts as a means of predictably controlling the electronic properties of colloidal QD films and as a versatile adjustable parameter in the performance optimization of QD optoelectronic devices.
    No preview · Article · May 2014 · ACS Nano
  • V. Sharikov-Bass · Q. Yang · R. R. Lunt
    [Show abstract] [Hide abstract]
    ABSTRACT: Introduction Previous investigations of Gadolinium-doped Cerium Oxide (GDC) have demonstrated its applicability for anode as well as electrolyte applications in Solid Oxide Fuel Cells (SOFCs) [1-3]. In particular, GDC has shown to be a desirable catalyst for CH4 fuel oxidation due to its ability to suppress carbon precipitation on SOFC anodes [4]. When used as an anode material, GDC must have a high oxygen surface exchange coefficient, kchem, to facilitate oxygen exchange. Previous efforts to measure GDC kchem values have utilized techniques such as thermo-gravimetric analysis (TGA) [2, 5] and electrical conductivity relaxation (ECR) [6]. At identical testing conditions the results of these measurements often differ by an order of magnitude, or more. The present work aims to help resolve these discrepancies by determining GDC kchem values through a recently-developed curvature relaxation (κR) technique [7]. Experimental Methods Following the procedure described in Ref. [7], the κR response of a mechano-chemically active film [8] (in this case, a 570 nm thick sputtered GDC thin film) on an inert substrate (in this case a 200 micron thick (100)-oriented (Y2O3)0.13(ZrO2)0.87 single crystal) equilibrating to an abrupt step in oxygen particle pressure, p(O­2), was used to measure kchem. Here, p(O2) was altered by switching between 2∙10-27/bar and 2∙10-28/bar at 600oC, and between 3.2∙10-29/bar and 3.2∙10-30/bar at 550oC. The p(O2) was controlled by switching between a 68 sccm dry H2-32 sccm 25oC humidifed H2 mixture and a 100 sccm 25oC humidified H2gas stream. Results and Discussion Fig. 1 shows the changes in bilayer curvature over multiple p(O2) cycles at 550oC and 600oC. The reproducibility in the long-term (i.e. equilibrium) curvatures of the oxidized and reduced stages suggest an absence of factors leading to irreproducibility; such as sample damage through cracking or delamination. The kchem values obtained by the κR technique are compared with literature in Fig. 2. The activation energy, Ea, of the κR-measured kchem is 0.4±0.1 eV, compared to 0.7 eV for literature ECR-measured kchem values [6]. The kchem values reported here are noticeably lower than those found in the literature for similar temperatures. While it is possible that this mismatch is due to the difference in the applied p(O2), the relationship between p(O2) and kchem in Fig. 2 does not immediately follow the reported trends. Identification of the source of these discrepancies is on-going, and will be discussed in this work. Acknowledgements This work was funded by the Army Research Office Award #W911NF-13-1-0404. The authors would also like to thank Christopher Traverse for assistance with film sputtering. References [1] M. Mogensen, N.M. Sammes, G.A. Tompsett, Solid State Ionics, 129 (2000) 63-94. [2] K. Yashiro, S. Onuma, A. Kaimai, Y. Nigara, T. Kawada, J. Mizusaki, K. Kawamura, T. Horita, H. Yokokawa, Solid State Ionics, 152–153 (2002) 469-476. [3] M. Sahibzada, B.C.H. Steele, K. Zheng, R.A. Rudkin, I.S. Metcalfe, Catalysis Today, 38 (1997) 459-466. [4] V.D. Belyaev, T.I. Politova, O.A. Mar'ina, V.A. Sobyanin, Applied Catalysis A, 133 (1995) 47-57. [5] S.R. Bishop, K.L. Duncan, E.D. Wachsman, Electrochimica Acta, 54 (2009) 1436-1443. [6] A. Karthikeyan, S. Ramanathan, Applied Physics Letters, 92 (2008) 243109-1 to 243109-3. [7] Q. Yang, T.E. Burye, R.R. Lunt, J.D. Nicholas, Solid State Ionics, 249-250 (2013) 123-128. [8] S.R. Bishop, K.L. Duncan, E.D. Wachsman, Acta Materialia, 57 (2009) 3596-3605.
    No preview · Conference Paper · May 2014
  • C. Jiang · R. R. Lunt · P. M. Duxbury · P. P. Zhang
    [Show abstract] [Hide abstract]
    ABSTRACT: ZnO is a versatile cathode buffer layer for organic photovoltaics (OPV) due to its appealing optical and electronic properties. Using the sol-gel method, we find that the processing temperature of ZnO cathode buffer layers significantly influences the device performance of inverted polymer OPVs composed of blended films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). In particular, ZnO processed at relatively low temperatures results in better device performance than those processed at higher temperatures despite the improved crystallinity and electron mobility of the latter. We attribute this finding to the tuning of the ZnO work function with the annealing temperature, which determines the interface energetics at the cathode and thus influences the open circuit voltage, series resistance and fill factor.
    No preview · Article · Jan 2014 · RSC Advances
  • Source
    Qing Yang · Theodore E. Burye · Richard R. Lunt · Jason D. Nicholas
    [Show abstract] [Hide abstract]
    ABSTRACT: Here, an in situ curvature relaxation (κR) method was used to measure chemical oxygen surface exchange coefficients (k's) under well-characterized stress, temperature, and oxygen partial pressure conditions. These k's were measured by analyzing the transient curvature of yttria stabilized zirconia supported La0.6Sr0.4FeO3 − δ thin films reacting to oxygen partial pressure step changes. The sputtered thin film k's measured here were consistent with extrapolated bulk sample k's, but larger than those reported for pulsed laser deposited thin films. This is the first time that the curvature response of a system has been used to characterize thin film oxygen surface exchange kinetics. The simultaneous measurement of film stress and k provided by the curvature relaxation method may help explain the large k discrepancies observed in the literature.
    Full-text · Article · Nov 2013 · Solid State Ionics
  • Qing Yang · Richard R. Lunt · Jason D. Nicholas
    [Show abstract] [Hide abstract]
    ABSTRACT: Mechano-chemical coupling of La0.6Sr0.4FeO 3-δ thin films were observed below 500°C for the first time using a curvature relaxation technique. Chemical oxygen surface exchange coefficients (k's) were measured by fitting the transient curvature of the thin film|substrate bilayer specimens under controlled temperature and oxygen partial pressure. Reproducible k values and their activation energies were obtained and are consistent with bulk sample k's extrapolated from the literature.
    No preview · Conference Paper · Oct 2013
  • [Show abstract] [Hide abstract]
    ABSTRACT: Integration of transparent photovoltaics into the building envelope creates unique opportunities to reduce the levelized electricity cost of solar power. However, this integration warrants consideration of the angular dependence of these devices as illumination around the building envelope is rarely at normal incidence. Here we correctly update transfer-matrix and equations to accurately model the quantum efficiency and optical properties under oblique illumination. We use this model to demonstrate the various angular performance characteristics possible for proof-of-concept optimizations of transparent planar-heterojunction solar cells and discuss considerations needed to fully account for optical, electrical, and positional configurations in this optimization.
    No preview · Article · Sep 2013 · Applied Physics Letters
  • Yimu Zhao · Richard R. Lunt

    No preview · Article · Sep 2013 · Advanced Energy Materials
  • Yimu Zhao · Richard R. Lunt
    [Show abstract] [Hide abstract]
    ABSTRACT: Integrating solar-harvesting systems into the building envelope is a transformative route to improving building effi ciency, capturing large areas of solar energy, and lowering effective solar cell installation costs by piggybacking on the installation, framing, and maintenance of the existing building envelope. However, the widespread adoption of such a pathway is typically hampered by diffi culties associated with mounting traditional photovoltaic (PV) modules in non-standard confi gurations on and around buildings due to added structural cost, architectural impedance, and most importantly, aesthetics. To overcome these hurdles we have developed a luminescent solar concentrator (LSC) employing novel nanocrystal-polymer blends that allow for selective ultraviolet light harvesting that results in a high degree of visible light transmittance. These transparent LSCs offer a different route to large area scaling with high defect tolerances compared to other transparent photovoltaic devices. These systems have signifi cant potential in 1) energy scavenging electronics displays, 2) autonomous electrochromicwindows, 3) visible-blind detectors, and 4) coatings for improved UV response and protection of traditional solar installations.
    No preview · Article · Sep 2013 · Laser Physics Review
  • Yimu Zhao · Richard Lunt
    [Show abstract] [Hide abstract]
    ABSTRACT: Luminescent solar concentrators (LSCs) have recently regained attention as a route for integration into the building envelope. To date, however, these systems have been limited to absorption and emission (glow) in the visible part of spectrum. We have designed and fabricated novel transparent luminescent solar concentrators devices composed of synthesized metal halide nanocrystal phosphorescent luminophores that allow for efficient and selective harvesting of ultraviolet (UV) photons with a near perfect absorption cutoff at the edge of the visible spectrum (430nm) while efficiently down-converting emitted light with a massive stoke shift to the near-infrared (800nm). We have demonstrated transparent LSCs with power efficiency of 0.8% ± 0.5%, system external quantum efficiency exceeding 35%, and an average transmittance of 82% ± 1%. We show through experiments and modeling that this architecture has the potential to exhibit up to 1-2% power conversion over module areas 1 m^2. These concentrators present new opportunities for non-tinted and highly-adoptable solar- windows that can translate into improved building efficiency, enhanced UV-barrier layers, and lower cost solar harvesting systems.
    No preview · Article · Mar 2013
  • Sean Wagner · Richard Lunt · Pengpeng Zhang
    [Show abstract] [Hide abstract]
    ABSTRACT: Control of highly ordered organic molecular thin films is currently of intense interest for integration into modern electronics due to the tunable nature of organic molecules. Here, we study the initial growth of archetypal zinc phthalocyanine (ZnPc) and copper phthalocyanine (CuPc) on the deactivated Si(111) surface. Using scanning probe microscopy (SPM), we demonstrate access to a new quasi-epitaxial anisotropic step-flow growth for both ZnPc and CuPc with a single dominant long-range ordered relationship between the organic crystalline film and the substrate, uniquely distinct from inorganic epitaxial step-flow growth. This growth mode is largely attributed to the molecular diffusion and preferential nucleation at step edges enabled by the deactivated Si surface. We demonstrate the transition of growth modes by varying substrate temperature during deposition, altering the balance between diffusion and step- and island- nucleation rates. Access to the anisotropic step-flow growth offers new potential for the integration of highly-ordered organic thin films in silicon-based electronics.
    No preview · Article · Mar 2013
  • Sean R Wagner · Richard R Lunt · Pengpeng Zhang
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the first demonstration of anisotropic step-flow growth of organic molecules on a semiconducting substrate using metal phthalocyanine thermally deposited on the deactivated Si(111)-B sqrt[3]×sqrt[3] R30° surface. With scanning probe microscopy and geometric modeling, we prove the quasiepitaxial nature of this step-flow growth that exhibits no true commensurism, despite a single dominant long-range ordered relationship between the organic crystalline film and the substrate, uniquely distinct from inorganic epitaxial growth. This growth mode can likely be generalized for a range of organic molecules on deactivated Si surfaces and access to it offers new potential for the integration of ordered organic thin films in silicon-based electronics.
    No preview · Article · Feb 2013 · Physical Review Letters
  • [Show abstract] [Hide abstract]
    ABSTRACT: PbS colloidal quantum dot heterojunction solar cells have shown significant improvements in performance, mostly based on devices that use high-temperature annealed transition metal oxides to create rectifying junctions with quantum dot thin films. Here, we demonstrate a solar cell based on the heterojunction formed between PbS colloidal quantum dot layers and CdS thin films that are deposited via a solution process at 80 °C. The resultant device, employing a 1,2-ethanedithiol ligand exchange scheme, exhibits an average power conversion efficiency of 3.5%. Through a combination of thickness-dependent current density-voltage characteristics, optical modeling, and capacitance measurements, the combined diffusion length and depletion width in the PbS quantum dot layer is found to be approximately 170 nm.
    No preview · Article · Feb 2013 · Nano Letters
  • [Show abstract] [Hide abstract]
    ABSTRACT: Organic photovoltaics devices typically utilize illumination through a transparent substrate, such as glass or an optically clear plastic. Utilization of opaque substrates, including low cost foils, papers, and textiles, requires architectures that instead allow illumination through the top of the device. Here, we demonstrate top-illuminated organic photovoltaics, employing a dry vapor-printed poly(3,4-ethylenedioxythiophene) (PEDOT) polymer anode deposited by oxidative chemical vapor deposition (oCVD) on top of a small-molecule organic heterojunction based on vacuum-evaporated tetraphenyldibenzoperiflanthene (DBP) and C60 heterojunctions. Application of a molybdenum trioxide (MoO3) buffer layer prior to oCVD deposition increases the device photocurrent nearly 10 times by preventing oxidation of the underlying photoactive DBP electron donor layer during the oCVD PEDOT deposition, and resulting in power conversion efficiencies of up to 2.8% for the top-illuminated, ITO-free devices, approximately 75% that of the conventional cell architecture with indium-tin oxide (ITO) transparent anode (3.7%). Finally, we demonstrate the broad applicability of this architecture by fabricating devices on a variety of opaque surfaces, including common paper products with over 2.0% power conversion efficiency, the highest to date on such fiber-based substrates.
    No preview · Article · Nov 2012 · Advanced Energy Materials
  • [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate series-integrated multijunction organic photovoltaics fabricated monolithically by vapor-deposition in a transposed subcell order with the near-infrared-absorbing subcell in front of the green-absorbing subcell. This transposed subcell order is enabled by the highly complementary absorption spectra of a near-infrared-absorbing visibly-transparent subcell and a visible-absorbing subcell and motivated by the non-spatially-uniform optical intensity in nanoscale photovoltaics. The subcell order and thicknesses are optimized via transfer-matrix formalism and short-circuit current simulations. An efficient charge recombination zone consisting of layers of BCP/Ag/MoOx leads to negligible voltage and series-resistance losses. Under 1-sun illumination the multijunction solar cells exhibit a power conversion efficiency of 5.5 ± 0.2% with an FF of 0.685 ± 0.002 and a V(OC) of 1.65 ± 0.02 V, corresponding to the sum of the V(OC) of the component subcells. These devices exhibit a broad spectral response (in the wavelength range of 350 nm to 850 nm) but are limited by subcell external quantum efficiencies between 20% and 30% over the photoactive spectrum.
    No preview · Article · Sep 2012 · Physical Chemistry Chemical Physics

Publication Stats

2k Citations
365.98 Total Impact Points


  • 2012-2015
    • Michigan State University
      • Department of Chemical Engineering and Materials Science
      Ист-Лансинг, Michigan, United States
  • 2011-2012
    • Massachusetts Institute of Technology
      • Department of Electrical Engineering and Computer Science
      Cambridge, Massachusetts, United States
  • 2007-2011
    • Princeton University
      • Department of Chemical and Biological Engineering
      Princeton, New Jersey, United States
  • 2010
    • University of Michigan
      • Department of Electrical Engineering and Computer Science (EECS)
      Ann Arbor, Michigan, United States
  • 2009
    • Concordia University–Ann Arbor
      Ann Arbor, Michigan, United States