5 research outputs found
Tris(2-(1<i>H</i>-pyrazol-1-yl)pyridine)cobalt(III) as p-Type Dopant for Organic Semiconductors and Its Application in Highly Efficient Solid-State Dye-Sensitized Solar Cells
Chemical doping is an important strategy to alter the charge-transport properties of both molecular and polymeric organic semiconductors that find widespread application in organic electronic devices. We report on the use of a new class of Co(III) complexes as p-type dopants for triarylamine-based hole conductors such as spiro-MeOTAD and their application in solid-state dye-sensitized solar cells (ssDSCs). We show that the proposed compounds fulfill the requirements for this application and that the discussed strategy is promising for tuning the conductivity of spiro-MeOTAD in ssDSCs, without having to rely on the commonly employed photo-doping. By using a recently developed high molar extinction coefficient organic D-π-A sensitizer and p-doped spiro-MeOTAD as hole conductor, we achieved a record power conversion efficiency of 7.2%, measured under standard solar conditions (AM1.5G, 100 mW cm<sup>–2</sup>). We expect these promising new dopants to find widespread applications in organic electronics in general and photovoltaics in particular
Subnanometer Ga<sub>2</sub>O<sub>3</sub> Tunnelling Layer by Atomic Layer Deposition to Achieve 1.1 V Open-Circuit Potential in Dye-Sensitized Solar Cells
Herein, we present the first use of a gallium oxide tunnelling
layer to significantly reduce electron recombination in dye-sensitized
solar cells (DSC). The subnanometer coating is achieved using atomic
layer deposition (ALD) and leading to a new DSC record open-circuit
potential of 1.1 V with state-of-the-art organic D-Ï€-A sensitizer
and cobalt redox mediator. After ALD of only a few angstroms of Ga<sub>2</sub>O<sub>3</sub>, the electron back reaction is reduced by more
than an order of magnitude, while charge collection efficiency and
fill factor are increased by 30% and 15%, respectively. The photogenerated
exciton separation processes of electron injection into the TiO<sub>2</sub> conduction band and the hole injection into the electrolyte
are characterized in detail
Influence of Donor Groups of Organic D−π–A Dyes on Open-Circuit Voltage in Solid-State Dye-Sensitized Solar Cells
In solid-state dye-sensitized solar cells (ssDSCs), the poor pore filling of the mesoporous semiconductor and the short diffusion length of charge carriers in the hole-transport material (HTM) have limited the mesoscopic titania layer to a thickness of 2–3 μm. To increase the amount of light harvested by ssDSCs, organic dyes with high molar extinction coefficients are of great importance and have been the focus of intensive research. Here we investigate ssDSCs using an organic D−π–A dye, coded Y123, and 2,2′,7,7′-tetrakis(<i>N</i>,<i>N</i>-di-<i>p</i>-methoxyphenylamine)-9,9′-spirobifluorene as a hole-transport material, exhibiting 934 mV open-circuit potential and 6.9% efficiency at standard solar conditions (AM1.5G, 100 mW cm<sup>–2</sup>), which is a significant improvement compared to the analogue dyes C218, C220, and JK2 (<i>V</i><sub>oc</sub> values of 795, 781, and 914 mV, respectively). An upward shift in the conduction band edge was observed from photovoltage transient decay and impedance spectroscopy measurements for devices sensitized with Y123 and JK2 dyes compared to the device using C220 as sensitizer, in agreement with the high photovoltage response of the corresponding ssDSCs. This work highlights the importance of the interaction between the HTM and the dye-sensitized TiO<sub>2</sub> surface for the design of ssDSCs
Regulating a Benzodifuran Single Molecule Redox Switch via Electrochemical Gating and Optimization of Molecule/Electrode Coupling
We report a novel strategy for the
regulation of charge transport
through single molecule junctions via the combination of external
stimuli of electrode potential, internal modulation of molecular structures,
and optimization of anchoring groups. We have designed redox-active
benzodifuran (BDF) compounds as functional electronic units to fabricate
metal–molecule–metal (m–M–m) junction
devices by scanning tunneling microscopy (STM) and mechanically controllable
break junctions (MCBJ). The conductance of thiol-terminated BDF can
be tuned by changing the electrode potentials showing clearly an off/on/off
single molecule redox switching effect. To optimize the response,
a BDF molecule tailored with carbodithioate (−CS<sub>2</sub><sup>–</sup>) anchoring groups was synthesized. Our studies
show that replacement of thiol by carbodithioate not only enhances
the junction conductance but also substantially improves the switching
effect by enhancing the on/off ratio from 2.5 to 8
Influence of the Donor Size in D−π–A Organic Dyes for Dye-Sensitized Solar Cells
We report two new molecularly engineered
push–pull dyes,
i.e., <b>YA421</b> and <b>YA422</b>, based on substituted
quinoxaline as a π-conjugating linker and bulky-indoline moiety
as donor and compared with reported <b>IQ4</b> dye. Benefitting
from increased steric hindrance with the introduction of bisÂ(2,4-dihexyloxy)Âbenzene
substitution on the quinoxaline, the electron recombination between
redox electrolyte and the TiO<sub>2</sub> surface is reduced, especially
in redox electrolyte employing CoÂ(II/III) complexes as redox shuttles.
It was found that the open circuit photovoltages of <b>IQ4</b>, <b>YA421</b>, and <b>YA422</b> devices with cobalt-based
electrolyte are higher than those with iodide/triiodide electrolyte
by 34, 62, and 135 mV, respectively. Moreover, the cells employing
graphene nanoplatelets on top of gold spattered film as a counter
electrode (CE) show lower charge-transfer resistance compared to platinum
as a CE. Consequently, <b>YA422</b> devices deliver the best
power conversion efficiency due to higher fill factor, reaching 10.65%
at AM 1.5 simulated sunlight. Electrochemical impedance spectroscopy
and transient absorption spectroscopy analysis were performed to understand
the electrolyte influence on the device performances with different
counter electrode materials and donor structures of donor−π–acceptor
dyes. Laser flash photolysis experiments indicate that even though
the dye regeneration of <b>YA422</b> is slower than that of
the other two dyes, the slower back electron transfer of <b>YA422</b> contributes to the higher device performance