4 research outputs found
Impact of Organic Hole Transporting Material and Doping on the Electrical Response of Perovskite Solar Cells
The
hole transport material (HTM) layer is a key component of the
perovskite solar cells (PSCs) that must be optimized to reach high
efficiency. The development of new HTMs alternative to Spiro-OMeTAD
and the understanding of the role of doping agents on these layers
are important research axes in the field. It requires the use of appropriate
characterization tools enabling us to discriminate the bulk and interface
effects. In the present paper, we fully analyze the effect of HTM
doping and of the material on the impedance response of PSCs. The
approach has been implemented on two different molecular HTMs, Spiro-OMeTAD
and a new molecular carbazole HTM, called B186, and with various doping
levels. We show that limitations by poor doping are characterized
by an extra high frequency impedance loop for which capacitance and
resistance analysis gives the dielectric constant and conductivity
of the material, respectively. However, the low-frequency part of
the spectra provides important information on the charge accumulation/outflow
and on the recombination levels. More generally, the presented approach
is of high practical interest for the development of new organic HTMs
and for the optimization of the layer doping
Processable Star-Shaped Molecules with Triphenylamine Core as Hole-Transporting Materials: Experimental and Theoretical Approach
In this study we report on the characterization of five
star-shaped
Ï-conjugated molecules by means of UVâvis absorption
spectroscopy and electrochemical cyclic voltammetry. These molecules,
with triphenylamine (TPA) core bearing one thienothiophene moiety
and a different number of thiophene ones, are designed as hole-transporting
materials for dye-sensitized solar cell (DSSC) applications. Theoretical
calculations employing the B3LYP functional are also carried out in
order to understand the structureâproperty relationships. UVâvis
absorption measurements and time-dependent density functional theory
(TDDFT) calculations show the presence of intense UVâvis bands
for all compounds. These bands are dominated by two degenerate ÏâÏ*
excitations mostly involving the HOMO â LUMO and HOMO â
LUMO+1 transitions. Electrochemical cyclic voltammetry and DFT calculations
show the HOMO (LUMO) energy levels increasing (decreasing) with the
number of conjugated heterocyclic rings in these molecules. The HOMO
energies have been found to vary between â5.38 and â5.13
eV thus showing good positioning with respect to the Fermi level of
gold electrode (DSSC applications). The calculated internal reorganization
energies (λ<sub>i</sub>) suggest for these materials promising
hole-transport properties. The analysis of the space extension of
the HOMO orbitals as a function of the number of conjugated rings
in these molecules gives useful information on their design
Panchromatic Photopolymerizable Cationic Films Using Indoline and Squaraine Dye Based Photoinitiating Systems
The photoinitiating abilities of
indoline and squaraine dyes (D102
and SQ02) incorporated in multicomponent systems for the cationic
polymerization of an epoxide or a vinyl ether have been investigated.
The polymerizable films exhibit a panchromatic character as revealed
by their photosensitivity to a halogen lamp (370â800 nm); household
LED bulbs centered at 462 nm (blue), 514 nm (green), 591 nm (yellow),
and 630 nm (red); and laser diodes at 457, 473, 532, and 635 nm. SQ02
is particularly efficient in the 520â700 nm range, while D102
exhibits a good efficiency in the 400â580 nm region. The radical
photopolymerization of an acrylate can also be observed particularly
at 635 nm or upon a halogen lamp. The photochemical mechanisms are
studied by steady state photolysis, fluorescence, cyclic voltammetry,
electron spin resonance spin trapping, and laser flash photolysis
techniques
Nanographene Coupled with Interfacial Pyrene Derivatives for Thermally Stable Perovskite Solar Cells
Although
high-efficiency perovskite solar cells (PSCs) have been
achieved using a hole-extracting material, spiro-MeOTAD, thermal stability
has been unattainable due to the low glass transition temperature
of spiro-MeOTAD and additives therein. Here, we report on the use
of nanographene-based hole-transporting materials coupled with a pyrene
derivative as an interface modifier for thermally stable and high
efficiency PSCs. Asymmetric methyl and methoxy groups are introduced
in the diphenylÂamino group that is attached to the hexa-peri-hexabenzoÂcoronene (HBC) nanographene core, coded
HBC-DPAMeOMe. 1-PyreneÂmethylÂammonium iodide is coupled
to enhance the chemical interaction between perovskite and HBC-DPAMeOMe,
which leads to a power conversion efficiency over 23%. A thermal stability
test at 85 °C for 1000 h reveals that 83.6% of the initial efficiency
(23.04% â 19.25%) is maintained for the device with HBC-DPAMeOMe,
while a significant degradation from 20.69% to 5.08% is observed for
the device with spiro-MeOTAD. Nanographene-based hole conductors shed
light on the thermal stability issue in PSCs