3 research outputs found
Effect of Bromine Substitution on the Ion Migration and Optical Absorption in MAPbI<sub>3</sub> Perovskite Solar Cells: The First-Principles Study
In the past few years,
the remarkable energy conversion efficiency of lead-halide-based perovskite
solar cells (PSCs) has drawn extraordinary attention. However, some
exposed problems in PSCs such as the low chemical stability and so
forth are tough to eliminate. A fundamental understanding of ionic
transport at the nanoscale is essential for developing high-performance
PSCs based on the anomalous hysteresis current–voltage (<i>I</i>–<i>V</i>) curves and the poor stability.
Our work is to understand the ionic transport mechanism by introducing
suitable halogen substitution with insignificant impact on light absorption
to hinder ion diffusion and thereby to seek a method to improve the
stability. Herein, we used first-principles density functional theory
(DFT) to calculate the band gaps and the optical absorption coefficients,
and the interstitial and the vacancy defect diffusion barriers of
halide in the orthogonal phase MAPbX<sub>3</sub> (MA = CH<sub>3</sub>NH<sub>3</sub>, X = I, Br, I<sub>0.5</sub>Br<sub>0.5</sub>) perovskite,
respectively. The research results show that a half bromine substitution
not only prevents ion migration in perovskite, but also maintains
a favorable light absorption capacity. It may be helpful to maintain
the PSC’s property of light absorption with a similar atomic
substitution. Furthermore, smaller atomic substitution for the halogen
atoms may be essential for increasing the diffusion barrier
First-Principles Screening and Design of Novel Triphenylamine-Based D−π–A Organic Dyes for Highly Efficient Dye-Sensitized Solar Cells
We screen a series
of π-conjugated bridge groups and design
a range of metal-free organic donor−π–acceptor
(D−π–A) <b>SPL101</b>–<b>SPL108</b> dyes based on the experimentally synthesized <b>C217</b> dye
for highly efficient dye-sensitized solar cells (DSSC) using density
functional theory (DFT) and time-dependent DFT (TDDFT), and further
calculate their physical and electronic properties, including geometrical
structures, electronic cloud distribution, molecular orbital energy
levels, absorption spectra, light harvesting efficiency (LHE), driving
force of injection (Δ<i>G</i><sub>inj</sub>) and regeneration
(Δ<i>G</i><sub>reg</sub>), and electron dipole moment
(μ<sub>normal</sub>). Results reveal that the π-conjugated
bridge groups in <b>SPL103</b> and <b>SPL104</b> are promising
functional groups for D−π–A organic dyes. In particular,<b> SPL106 </b>and<b> SPL108</b> have not only smaller energy
gaps, higher molar extinction coefficients, and 128 and 143 nm redshifts,
but also a broader absorption spectrum covering the entire visible
range up to the near-IR region of 1200 nm compared to <b>C217</b> dye
Rational Design of Dithienopicenocarbazole-Based Dyes and a Prediction of Their Energy-Conversion Efficiency Characteristics for Dye-Sensitized Solar Cells
A series of metal-free
organic donor–acceptor (D–A) derivatives (<b>ME01</b>–<b>ME06</b>) of the known dye <b>C281</b> were
designed using first-principles calculations in order to evaluate
their potential for applications in dye-sensitized solar cells (DSSCs).
Their physical and electronic properties were calculated using density
functional theory (DFT) and time-dependent density functional theory
(TD-DFT). These include molecular properties that are required to
assess the feasibility of a dye to function in DSSCs: UV–vis
absorption spectra, light-harvesting efficiency (LHE), and driving
forces of electron injection (<i>Δ<i>G</i></i><sub>inj</sub>). <b>ME01</b>, <b>ME02</b>, and <b>ME04</b> are predicted to exhibit broad absorption optical spectra
that cover the entire visible range, rendering these three dyes promising
DSSC prospects. Device-relevant calculations on these three short-listed
dyes and the parent dye <b>C281</b> were then performed, whereupon
the dye molecules were adsorbed onto anatase TiO<sub>2</sub> surfaces
to form the DSSC working electrode. Associated DSSC device characteristics
of this dye···TiO<sub>2</sub> interfacial structure
were determined. These include the light-harvesting efficiency, the
number of injected electrons, the electron-injection lifetime, and
the quantum-energy alignment of the adsorbed dye molecule to that
of its device components. In turn, these calculated parameters enabled
the derivation of the DSSC device performance parameters: short-circuit
current density, <i>J</i><sub>SC</sub>, incident photon-to-electron
conversion efficiency, IPCE, and open-circuit voltage, <i>V</i><sub>OC</sub>. Thus, we demonstrate a systematic <i>ab initio</i> approach to screen rationally designed D–A dyes with respect
to their potential applicability in high-performance DSSC devices