32 research outputs found
Small Molecule Anchored to Mesoporous ITO for High-Contrast Black Electrochromics
We
developed transmissive-to-black electrochromic devices by assembling <i>p</i>-aminotriphenlyamine (pAT) on the surface of mesoporous
tin-doped indium oxide (mITO) electrodes. pAT-modified electrodes
possess an optical contrast ratio of up to 64%, switching speeds of
1â4 s, and enhanced chemical reversibility as compared to unbound
pAT in solution. Gel permeation chromatography (GPC) and inductively
coupled plasma mass spectrometry (ICP-MS) were used to analyze the
electrochemical degradation products of pAT-modified electrodes and
pAT in solution. The rare transparent-to-black electrochromism of
pAT makes it a promising small-molecule, anodically coloring material
for smart window applications
PolymerâNanoparticle Electrochromic Materials that Selectively Modulate Visible and Near-Infrared Light
In
this manuscript, we describe a class of hybrid electrochromic
materials utilizing polythiophenes and tin-doped indium oxide (ITO)
nanoparticles that independently modulate visible and near-infrared
(NIR) light. By altering the voltage applied across electrodes modified
with these composite materials, the electrodes can be repeatedly switched
between three distinct modes of operation. These âbright and
warmâ, âbright and coolâ, and âdark and
coolâ modes vary in their visible and NIR transmission properties
and are targeted toward the development of smart windows that can
control both solar lighting and heating fluxes. Electrodes containing
the composite films, which are fabricated by electropolymerizing polythiophenes
on transparent electrodes coated with ITO nanoparticles, possess fast
switching times (<90 s), moderate durability, and contrast ratios
similar to those of the individual composite components. The maximum
contrast ratios of the composite systems are 47% at 700 nm and 39%
at 1250 nm. After 200 switching cycles, these contrast ratios degrade
by 15â20%. The composite materials developed here represent
a new direction of research aimed at modulating light and heat flux
in smart windows
Enhancing the Hole-Conductivity of Spiro-OMeTAD without Oxygen or Lithium Salts by Using Spiro(TFSI)<sub>2</sub> in Perovskite and Dye-Sensitized Solar Cells
2,2â˛,7,7â˛-TetrakisÂ(<i>N,N</i>-di-<i>p</i>-methoxyphenylamine)-9,9â˛-spirobifluorene
(spiro-OMeTAD),
the prevalent organic hole transport material used in solid-state
dye-sensitized solar cells and perovskite-absorber solar cells, relies
on an uncontrolled oxidative process to reach appreciable conductivity.
This work presents the use of a dicationic salt of spiro-OMeTAD, named
spiroÂ(TFSI)<sub>2</sub>, as a facile means of controllably increasing
the conductivity of spiro-OMeTAD up to 10<sup>â3</sup> S cm<sup>â1</sup> without relying on oxidation in air. SpiroÂ(TFSI)<sub>2</sub> enables the first demonstration of solid-state dye-sensitized
solar cells fabricated and operated with the complete exclusion of
oxygen after deposition of the sensitizer with higher and more reproducible
device performance. Perovskite-absorber solar cells fabricated with
spiroÂ(TFSI)<sub>2</sub> show improved operating stability in an inert
atmosphere. Gaining control of the conductivity of the HTM in both
dye-sensitized and perovskite-absorber solar cells in an inert atmosphere
using spiroÂ(TFSI)<sub>2</sub> is an important step toward the commercialization
of these technologies
Chlorine in PbCl<sub>2</sub>âDerived Hybrid-Perovskite Solar Absorbers
Chlorine in PbCl<sub>2</sub>âDerived Hybrid-Perovskite
Solar Absorber
Mechanism of Tin Oxidation and Stabilization by Lead Substitution in Tin Halide Perovskites
The recent development
of efficient binary tin- and lead-based
metal halide perovskite solar cells has enabled the development of
all-perovskite tandem solar cells, which offer a unique opportunity
to deliver high performance at low cost. Tin halide perovskites, however,
are prone to oxidation, where the Sn<sup>2+</sup> cations oxidize
to Sn<sup>4+</sup> upon air exposure. Here, we identify reaction products
and elucidate the oxidation mechanism of both ASnI<sub>3</sub> and
ASn<sub>0.5</sub>Pb<sub>0.5</sub>I<sub>3</sub> (where A can be made
of methylammonium, formamidinium, cesium, or a combination of these)
perovskites and find that substituting lead onto the B site fundamentally
changes the oxidation mechanism of tin-based metal halide perovskites
to make them more stable than would be expected by simply considering
the decrease in tin content. This work provides guidelines for developing
stable small band gap materials that could be used in all-perovskite
tandems
Ternary Bulk Heterojunction Solar Cells: Addition of Soluble NIR Dyes for Photocurrent Generation beyond 800 nm
The
incorporation of a <i>tert</i>-butyl-functionalized silicon
2,3-naphthalocyanine bisÂ(trihexylsilyloxide) dye molecule as a third
component in a ternary blend bulk heterojunction (BHJ) organic solar
cell containing P3HT (donor) and PC<sub>60</sub>BM (acceptor) results
in increased NIR absorption. This absorption yields an increase of
up to 40% in the short-circuit current and up to 19% in the power
conversion efficiency (PCE) in photovoltaic devices. Two-dimensional
grazing incidence wide-angle X-ray scattering (2-D GIWAXS) experiments
show that compared to the unfunctionalized dye the <i>tert</i>-butyl functionalization enables an increase in the volume fraction
of the dye molecule that can be incorporated before the device performance
decreases. Quantum efficiency and absorption spectra also indicate
that, at dye concentrations above about 8 wt %, there is an approximately
30 nm red shift in the main silicon naphthalocyanine absorption peak,
allowing further dye addition to contribute to added photocurrent.
This peak shift is not observed in blends with unfunctionalized dye
molecules, however. This simple approach of using ternary blends may
be generally applicable for use in other unoptimized BHJ systems towards
increasing PCEs beyond current levels. Furthermore, this may offer
a new approach towards OPVs that absorb NIR photons without having
to design, synthesize, and purify complicated donorâacceptor
polymers
Minimal Effect of the Hole-Transport Material Ionization Potential on the Open-Circuit Voltage of Perovskite Solar Cells
Hole-transport material optimization
is an important step toward
maximizing the efficiency of perovskite solar cells. Here, we investigate
the role of one hole-transport material property, the ionization potential,
on the performance of perovskite solar cells. We employ a device architecture
that allows us to systematically tune the ionization potential while
avoiding any impact to other device parameters, and we find that for
a wide range of ionization potentials the photovoltaic performance
is minimally affected. This finding relaxes the requirement for the
development of hole-transport materials with particular ionization
potentials, allowing for the optimization of hole-transport materials
that can improve performance in differing ways such as through increased
stability or decreased parasitic absorption
Thermal Stability of Mixed Cation Metal Halide Perovskites in Air
We study the thermal
stability in air of the mixed cation organicâinorganic
lead halide perovskites Cs<sub>0.17</sub>FA<sub>0.83</sub>PbÂ(I<sub>0.83</sub>Br<sub>0.17</sub>)<sub>3</sub> and Cs<sub>0.05</sub>(MA<sub>0.17</sub>FA<sub>0.83</sub>)<sub>0.95</sub>PbÂ(I<sub>0.83</sub>Br<sub>0.17</sub>)<sub>3</sub>. For the latter compound, containing both
MA<sup>+</sup> and FA<sup>+</sup> ions, thermal decomposition of the
perovskite phase was observed to occur in two stages. The first stage
of decomposition occurs at a faster rate compared to the second stage
and is only observed at relatively low temperatures (<i>T</i> < 150 °C). For the second stage, we find that both decomposition
rate and the activation energy have similar values for Cs<sub>0.05</sub>(MA<sub>0.17</sub>FA<sub>0.83</sub>)<sub>0.95</sub>PbÂ(I<sub>0.83</sub>Br<sub>0.17</sub>)<sub>3</sub> and Cs<sub>0.17</sub>FA<sub>0.83</sub>PbÂ(I<sub>0.83</sub>Br<sub>0.17</sub>)<sub>3</sub>, which suggests
that the first stage mainly involves reaction of MA<sup>+</sup> and
the second stage mainly FA<sup>+</sup>
Hole Transport Materials with Low Glass Transition Temperatures and High Solubility for Application in Solid-State Dye-Sensitized Solar Cells
We present the synthesis and device characterization of new hole transport materials (HTMs) for application in solid-state dye-sensitized solar cells (ssDSSCs). In addition to possessing electrical properties well suited for ssDSSCs, these new HTMs have low glass transition temperatures, low melting points, and high solubility, which make them promising candidates for increased pore filling into mesoporous titania films. Using standard device fabrication methods and Z907 as the sensitizing dye, power conversion efficiencies (PCE) of 2.94% in 2-Îźm-thick cells were achieved, rivaling the PCE obtained by control devices using the state-of-the-art HTM spiro-OMeTAD. In 6-Îźm-thick cells, the device performance is shown to be higher than that obtained using spiro-OMeTAD, making these new HTMs promising for preparing high-efficiency ssDSSCs
Molecular Engineering of Organic Dyes for Improved Recombination Lifetime in Solid-State Dye-Sensitized Solar Cells
A major limitation of solid-state
dye-sensitized solar cells is
a short electron diffusion length, which is due to fast recombination
between electrons in the TiO<sub>2</sub> electron-transporting layer
and holes in the 2,2â˛,7,7â˛-tetrakisÂ(<i>N</i>,<i>N</i>-di-<i>p</i>-methoxyphenylamine)-9,9â˛-spirobifluorene
(Spiro-OMeTAD) hole-transporting layer. In this report, the sensitizing
dye that separates the TiO<sub>2</sub> from the Spiro-OMeTAD was engineered
to slow recombination and increase device performance. Through the
synthesis and characterization of three new organic D-Ď-A sensitizing
dyes (WN1, WN3, and WN3.1), the quantity and placement of alkyl chains
on the sensitizing dye were found to play a significant role in the
suppression of recombination. In solid-state devices using Spiro-OMeTAD
as the hole-transport material, these dyes achieved the following
efficiencies: 4.9% for WN1, 5.9% for WN3, and 6.3% for WN3.1, compared
to 6.6% achieved with Y123 as a reference dye. Of the dyes investigated
in this study, WN3.1 is shown to be the most effective at suppressing
recombination in solid-state dye-sensitized solar cells, using transient
photovoltage and photocurrent measurements