3 research outputs found
Easily Attainable Phenothiazine-Based Polymers for Polymer Solar Cells: Advantage of Insertion of <i>S</i>,<i>S</i>-dioxides into its Polymer for Inverted Structure Solar Cells
Two donor– (D−) acceptor (A) type polymers
based
on a soluble chromophore of phenothiazine (PT) unit that is a tricyclic
nitrogen–sulfur heterocycle, have been synthesized by introducing
an electron-deficient benzothiadiazole (BT) building block copolymerized
with either PT or phenothiazine-<i>S</i>,<i>S</i>-dioxide (PT-<i>SS</i>) unit as an oxidized form of PT.
The resulting polymers, <b>PPTDTBT</b> and <b>PPTDTBT-</b><i><b>SS</b></i> are fully characterized by UV–vis
absorption, electrochemical cyclic voltammetry, X-ray diffraction
(XRD), and DFT theoretical calculations. We find that the maximum
absorption of <b>PPTDTBT</b> is not only markedly red-shifted
with respect to that of <b>PPTDTBT-</b><i><b>SS</b></i> but also its band gap as well as molecular energy levels
are readily tuned by the insertion of <i>S</i>,<i>S</i>-dioxides into the polymer. The main interest is focused on the electronic
applications of the two polymers in organic field-effect transistors
(OFETs) as well as conventional and inverted polymeric solar cells
(PSCs). <b>PPTDTBT</b> is a typical p-type polymer semiconductor
for OFETs and conventional PSCs based on this polymer and PC<sub>71</sub>BM show a power conversion efficiency (PCE) of 1.69%. In case of <b>PPTDTBT-</b><i><b>SS</b></i>, the devices characteristics
result in: (i) 1 order of magnitude higher hole mobility (μ
= 6.9 × 10<sup>–4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) than that obtained with <b>PPTDTBT</b> and (ii) improved performance of the inverted PSCs (1.22%), compared
to its conventional devices. Such positive features can be accounted
for in terms of closer packing molecular characteristics owing either
to the effects of dipolar intermolecular interactions orientated from
the sulfonyl groups or the relatively high coplanarity of <b>PPTDTBT-</b><i><b>SS</b></i> backbone
Semicrystalline D–A Copolymers with Different Chain Curvature for Applications in Polymer Optoelectronic Devices
Thiophene- and thienothiophene-based
donor–acceptor (D–A)
type semicrystalline copolymers with different backbone curvatures, <b>PTBT14</b> and <b>PTTBT14</b>, were designed and synthesized.
Both the polymers exhibit a nearly planar structure via noncovalent
S···O and C–H···N attractive
interactions, etc., in the polymer chain. <b>PTTBT14</b> is
linear, whereas <b>PTBT14</b> is curved owing to ∼160°
bond angle of the thiophene linkage. <b>PTTBT14</b> showed the
higher degree of interchain ordering with edge-on orientation, resulting
in efficient charge transport (0.26 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> for <b>PTTBT14</b> compared to 0.02
cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> for <b>PTBT14</b>) in PFETs with remarkable morphological stability and
no deterioration in device properties at temperatures up to 250 °C.
On the other hand, the curved shape of <b>PTBT14</b> attributed
to its improved photovoltaic properties with a power conversion efficiency
of 5.56%. The linear <b>PTTBT14</b> showed much stronger self-interactions
with negligible morphological changes and little miscibility with
PC<sub>61</sub>BM, showing the poor photovoltaic characteristics
Organic Solar Cells Fabricated by One-Step Deposition of a Bulk Heterojunction Mixture and TiO<sub>2</sub>/NiO Hole-Collecting Agents
Organic solar cells (OSCs) were fabricated using a one-step
deposition
of a mixture of NiO nanoparticles, region-regular polyÂ(3-hexylthiophene)
(P3HT), and [6,6]-phenyl-C<sub>61</sub>-butyric methyl ester (PCBM)
without polyÂ(3,4-ethylenedioxythiophene):polyÂ(styrenesulfonate) (PEDOT:PSS).
Although the intended NiO layer was successfully formed at the interface
between indium tin oxide (ITO) and the photoactive layer, only a marginal
increase in the power conversion efficiency (PCE) of the OSCs (from
0.773 to 1.171%) was found by addition of NiO nanoparticles to the
solution of the P3HT/PCBM mixture. Using X-ray photoelectron spectroscopy,
it was evidenced that P3HT was oxidized at interfaces of P3HT and
NiO, which can decrease the photovoltaic performance of an OSC. Ultrathin
TiO<sub>2</sub> wrapping layers (thickness ∼ 2 nm) on the surface
of NiO nanoparticles prepared by atomic layer deposition quenched
oxidation of P3HT resulted in a significant increase in PCE up to
2.684%. Our result shows that, in OSCs, oxidation of active polymers
at oxide/polymer interfaces should be of concern, and a strategy for
avoiding such degradation of polymers is required. Fabrication of
various core–shell nanostructures as oxide buffers can be useful
for quenching the oxidation of active polymers and increasing photovoltaic
performances