6 research outputs found
Photoelectric Memory Effect in an Organic Bulk Heterojunction Device
We
report on a memory effect observed in an inverted bulk heterojunction
organic photovoltaic device, where the electron-collecting electrode
is ZnO nanowires grown on an indium tin oxide (ITO) substrate. The
device presented a unique response to light by switching from a rectifying
behavior in the dark to a resistive response under illumination. After
cessation of light, the device slowly stabilized back to its rectifying
nature after ∼270 min, introducing a volatile photoelectric
memory effect. The reversibility of the response is verified through
multiple cycles of light exposure and placing the device in the dark.
The device is also illuminated with different light intensities to
study the photovoltaic response through I–V characterization.
It is found that the time constant associated with the transition
between the rectifying and resistive characteristics is independent
from the light intensity. Further study revealed that there is a hysteresis
loop in the I–V curve in the dark, but the loop vanished in
the resistive mode under illumination. A mechanism based on oxygen
absorption–desorption has been suggested to explain the observed
effect. Such a memory effect can be used in various optoelectronic
devices to save the optical information for an extended time
Large Photocurrent Response and External Quantum Efficiency in Biophotoelectrochemical Cells Incorporating Reaction Center Plus Light Harvesting Complexes
Bacterial photosynthetic reaction
centers (RCs) are promising materials
for solar energy harvesting, due to their high ratio of photogenerated
electrons to absorbed photons and long recombination time of generated
charges. In this work, photoactive electrodes were prepared from a
bacterial RC-light-harvesting 1 (LH1) core complex, where the RC is
encircled by the LH1 antenna, to increase light capture. A simple
immobilization method was used to prepare RC-LH1 photoactive layer.
Herein, we demonstrate that the combination of pretreatment of the
RC-LH1 protein complexes with quinone and the immobilization method
results in biophotoelectrochemical cells with a large peak transient
photocurrent density and photocurrent response of 7.1 and 3.5 μA
cm<sup>–2</sup>, respectively. The current study with monochromatic
excitation showed maximum external quantum efficiency (EQE) and photocurrent
density of 0.21% and 2 μA cm<sup>–2</sup>, respectively,
with illumination power of ∼6 mW cm<sup>–2</sup> at
∼875 nm, under ambient conditions. This work provides new directions
to higher performance biophotoelectrochemical cells as well as possibly
other applications of this broadly functional photoactive material
Hybrid Wiring of the Rhodobacter sphaeroides Reaction Center for Applications in Bio-photoelectrochemical Solar Cells
The
growing demand for nonfossil fuel-based energy production has drawn
attention to the utilization of natural proteins such as photosynthetic
reaction center (RC) protein complexes to harvest solar energy. The
current study reports on an immobilization method to bind the wild
type Rhodobacter sphaeroides RC from
the primary donor side onto a Au electrode using an immobilized cytochrome <i>c</i> (cyt <i>c</i>) protein via a docking mechanism.
The new structure has been assembled on a Au electrode by layer-by-layer
deposition of a carboxylic acid-terminated alkanethiol (HOOC (CH<sub>2</sub>)<sub>5</sub>S) self-assembled monolayer (SAM), and layers
of cyt <i>c</i> and RC. The Au|SAM|cyt <i>c</i>|RC working electrode was applied in a three-probe electrochemical
cell where a peak cathodic photocurrent density of 0.5 μA cm<sup>–2</sup> was achieved. Further electrochemical study of the
Au|SAM|cyt <i>c</i>|RC structure demonstrated ∼70%
RC surface coverage. To understand the limitations in the electron
transfer through the linker structure, a detailed energy study of
the SAM and cyt <i>c</i> was performed using photochronoamperometry,
ellipsometry, photoemission spectroscopy, and cyclic voltammetry (CV).
Using a simple rectangle energy barrier model, it was found that the
electrode work function and the large barrier of the SAM are accountable
for the low conductance in the devised linker structure
Sequential Laser-Burned Lignin and Hydrogen Evolution-Assisted Copper Electrodeposition to Manufacture Wearable Electronics
In the contemporary world, wearable electronics and smart
textiles/fabrics
are galvanizing a transformation of the health care, aerospace, military,
and commercial industries. However, a major challenge that exists
is the manufacture of electronic circuits directly on fabrics. In
this work, we addressed the issue by developing a sequential manufacturing
process. First, the target fabric was coated with a customized ink
containing lignin. Next, a desired circuit layout was patterned by
laser burning lignin, converting it to carbon and establishing a conductive
template on the fabric. At last, using an in-house-designed printer,
a devised localized hydrogen evolution-assisted (HEA) copper electroplating
method was applied to metalize the surface of the laser-burned lignin
pattern to achieve a very low resistive circuit layout (0.103 Ω
for a 1 cm long interconnect). The nanostructure and material composition
of the different layers were investigated via scanning electron microscopy,
energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and
Fourier-transform infrared spectroscopy (FTIR). Monitoring the conductivity
change before and after bending, rolling, stretching, washing, and
adhesion tests presented remarkable mechanical stability due to the
entanglement of the copper nanostructure to the fibers of the fabric.
Furthermore, the HEA method was used to solder a light-emitting diode
to a patterned circuit on the fabric by growing copper at the terminals,
creating interconnects. The presented sequential printing method has
the potential for fabricating reliable wearable electronics for various
applications, particularly in medical monitoring
Sequential Laser-Burned Lignin and Hydrogen Evolution-Assisted Copper Electrodeposition to Manufacture Wearable Electronics
In the contemporary world, wearable electronics and smart
textiles/fabrics
are galvanizing a transformation of the health care, aerospace, military,
and commercial industries. However, a major challenge that exists
is the manufacture of electronic circuits directly on fabrics. In
this work, we addressed the issue by developing a sequential manufacturing
process. First, the target fabric was coated with a customized ink
containing lignin. Next, a desired circuit layout was patterned by
laser burning lignin, converting it to carbon and establishing a conductive
template on the fabric. At last, using an in-house-designed printer,
a devised localized hydrogen evolution-assisted (HEA) copper electroplating
method was applied to metalize the surface of the laser-burned lignin
pattern to achieve a very low resistive circuit layout (0.103 Ω
for a 1 cm long interconnect). The nanostructure and material composition
of the different layers were investigated via scanning electron microscopy,
energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and
Fourier-transform infrared spectroscopy (FTIR). Monitoring the conductivity
change before and after bending, rolling, stretching, washing, and
adhesion tests presented remarkable mechanical stability due to the
entanglement of the copper nanostructure to the fibers of the fabric.
Furthermore, the HEA method was used to solder a light-emitting diode
to a patterned circuit on the fabric by growing copper at the terminals,
creating interconnects. The presented sequential printing method has
the potential for fabricating reliable wearable electronics for various
applications, particularly in medical monitoring
The Role of Gold-Adsorbed Photosynthetic Reaction Centers and Redox Mediators in the Charge Transfer and Photocurrent Generation in a Bio-Photoelectrochemical Cell
Bacterial photosynthetic reaction centers (RCs) are promising
materials
for solar energy harvesting, due to their high quantum efficiency.
A simple approach for making a photovoltaic device is to apply solubilized
RCs and charge carrier mediators to the electrolyte of an electrochemical
cell. However, the adsorption of analytes on the electrodes can affect
the charge transfer from RCs to the electrodes. In this work, photovoltaic
devices were fabricated incorporating RCs from purple bacteria, ubiquinone-10
(Q2), and cytochrome c (Cyt c) (the latter two species acting as redox
mediators). The adsorption of each of these three species on the gold
working electrode was investigated, and the roles of adsorbed species
in the photocurrent generation and the cycle of charge transfer were
studied by a series of photochronoamperometric, X-ray photoelectron
spectroscopy (XPS), atomic force microscopy (AFM), and cyclic voltammetry
(CV) tests. It was shown that both redox mediators were required for
photocurrent generation; hence, the RC itself is likely unable to
inject electrons into the gold electrode directly. The reverse redox
reactions of mediators at the electrodes generates electrical current.
Cyclic voltammograms for the RC-exposed gold electrode revealed a
redox couple due to the adsorbed RC at ∼ +0.5 V (vs
NHE), which confirmed that the RC was still redox active, upon adsorption
to the gold. Photochronoamperometric studies also indicated that RCs
adsorb, and are strongly bound to the surface of the gold, retaining
functionality and contributing significantly to the process of photocurrent
generation. Similar experiments showed the adsorption of Q2 and Cyt
c on unmodified gold surfaces. It was indicated by the photochronoamperometric
tests that the photocurrent derives from Q2-mediated charge transfer
between the RCs and the gold electrode, while solubilized Cyt c mediates
charge transfer between the P-side of adsorbed RC and the Pt counter
electrode. Also, the stability of the adsorbed RCs and mediators was
evaluated by measuring the photocurrent response over a period of
1 week. It is found that ∼46% of the adsorbed RCs remain active
after a week under aerobic conditions. A significantly extended lifetime
is expected by removing oxygen from the electrolyte and sealing the
device