A new
molecular Br2-catalyzed polymerization of 2,5-dibromo-3,4-ethylenedioxyselenophene
(DBEDOS), 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT), and their
analogues, providing metal free and virtually defect free conducting
polymers under mild reaction conditions. The resulting poly(3,4-ethylenedioxyselenophene)
(PEDOS), poly(3,4-ethylenedioxythiophene) (PEDOT) and their analogues
are electroactive, highly conducting and shown optoelectronic properties
practically identical to electrochemically prepared insoluble thin
films. This polymerization is a rare example of metal free polymerization
which lead to the formation of conjugated polymer. Details characterizations
of the obtained polymers were carried out and spectroelectrochemistry
of PEDOS-C12 film obtained by Br2-catalyzed
polymerization suggest higher conductivity and transparency compared
to PEDOS-C12 film obtained by other methods.
In the present work, poly(3‐hexylthiophene)‐block‐poly(hexyl‐3,4‐ethylenedioxythiophene) (P3HT‐b‐PEDOT‐C6) copolymer was synthesized by Kumada catalyst transfer polymerization (KCTP) by using 1:1 molar ratio of the corresponding monomers. For comparison purpose homopolymers, poly(3‐hexylthiophene) (P3HT) and poly(hexyl‐3,4‐ethylenedioxythiophene) (PEDOT‐C6) were obtained by using the conditions described for the block polymer. These polymers were obtained via chain‐growth mechanism using a catalytic amount of (0.03 molar equivalent) Ni(dppp)Cl2 in tetrahydrofuran (THF) in high yield after Soxhlet extraction. The synthesized block copolymer and homopolymers were well characterized by using 1H NMR, gel permeation chromatography (GPC) and FT‐IR spectroscopy. The optoelectronic properties of these copolymer and homopolymers were measured by using UV‐vis‐NIR spectra and cyclic voltammetry (CV). The thermal stability and surface morphology of these polymers were studied by using thermogravimetric analysis (TGA) and atomic force microscopy (AFM). The experimental results clearly indicated that the block copolymer show significantly different properties compared to their constituent homopolymers, which may be a potential member for optoelectronic applications.
We first time report poly(styrene sulfonate) (PSS) free poly(3,4ethylenedioxythiophene) (PEDOT) as a novel solution-processable hole transport layer (HTL) for organic solar cells. The transparent and conducting PEDOT thin film was obtained by solid state polymerization (SSP) of 2,5-dibromo-3,4-ethylenedioxythiophene (DBEDOT) on ITO coated glass substrate (by heating of the monomer at 60 8C for overnight). The thicknesses of the obtained thin films were optimized by using different concentrations of DBEDOT in chlorobenzene during spin coating. Two different combinations of active layers such as poly(3-hexylthiophene):phenyl-C 61 -butyric acid methyl ester (P3HT:PC 61 BM) and poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]:phenyl-C 71 -butyric acid methyl ester (PCDTBT:PC 71 BM) were used for device fabrication. Power conversion efficiencies were achieved up to 0.71 % and 1.70 % in a simple geometry of ITO/ssp-PEDOT/active layer/Al under ambient conditions. The potential importances of the ssp-PEDOT as an HTL are robust, stable, PSS free and solution-processable for organic solar cells.
In
this work, we report copper bromide (CuBr) as an efficient, inexpensive,
and solution-processable hole transport layer (HTL) for organic solar
cells (OSCs) for the first time. To examine the effectiveness of the
material in general, three different solvents such as acetonitrile
(MeCN), dimethyl sulfoxide (DMSO), and dimethylformamide (DMF) are
used for solution-processing thin-film deposition of CuBr. CuBr thin
films deposited from different solvents show high transparency and
no significant difference has been observed in absorption in the visible
and near-IR range, whereas a slight difference has been found in the
near-UV range by changing the solvents. Furthermore, two most studied
combinations of the active layer such as PTB7/PC
71
BM and
PCDTBT:/PC
71
BM are used for device fabrication with geometry
of ITO/CuBr(HTL) active layer/Al. By using CuBr as a HTL in OSCs,
the power conversion efficiencies (PCEs) have been achieved to up
to 5.16 and 4.72% with PTB7/PC
71
BM and PCDTBT/PC
71
BM active layers, respectively. The CuBr film from DMF solvent shows
highest PCE as compared to films deposited from DMSO and MeCN solvents.
Different solvents used for HTL deposition have a major effect on
the fill factor (FF), while very little difference on open circuit
voltage (
V
oc
) and short circuit current
(
J
sc
) has been observed. It may be mentioned
here that a small difference of device parameters (PCE, FF,
J
sc
, and
V
oc
) has
been observed in the devices using the HTL deposited from DMF and
DMSO solvents, whereas a significant difference of the device parameters
has been found in devices using the HTL from MeCN solvent.
Three copolymers based on poly(dialkoxybenzo[1,2‐b:4,5‐b′]dithiophene‐biselenophene) P3a and its heteroatom(s) analogues P3b and P3c are synthesized by Stille cross‐coupling to investigate the effects of the heteroatom on the optoelectronic and photovoltaic properties. Detailed characterizations of the copolymers are carried out by 1H NMR, gel permeation chromatography, UV–vis absorption spectroscopy, and cyclic voltammetry. Optical absorption spectra reveal that the presence of biselenophene moiety in the copolymer P3a shows red‐shifted absorption (band gap 1.82 eV) compared to bithiophene containing copolymer P3b (band gap 1.91 eV), while band gap of bifuran containing copolymer P3c is 2.05 eV. The photovoltaic devices are fabricated using the copolymers P3a–c blended with phenyl‐C71‐butyric acid methyl ester as an acceptor material with the device structure of indium tin oxide (ITO)/MoO3/active layer/Al. The power conversion efficiency is gradually increased with the replacement of furan by thiophene and furthermore thiophene by selenophene, respectively, due to increment in J
sc. Density functional theory calculations are studied on these three copolymers to understand the trends of energy levels and throughout compared with experimental data where applicable. The strategy has advantage of different aromaticities of heterocyclic rings combining with electronegativities and polarizabilities of the heteroatom(s) to allow the band gap engineering and tunability of photovoltaic performances.
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