4 research outputs found
Bulk Heterojunction versus Diffused Bilayer: The Role of Device Geometry in Solution p-Doped Polymer-Based Solar Cells
We exploit the effect of molecular p-type doping of P3HT in diffused bilayer (DB) polymer solar cells. In this alternative device geometry, the p-doping is accomplished in solution by blending the F<sub>4</sub>-TCNQ with P3HT. The p-doping both increases the film conductivity and reduces the potential barrier at the interface with the electrode. This results in an excellent power conversion efficiency of 4.02%, which is an improvement of âź48% over the p-doped standard bulk heterojunction (BHJ) device. Combined <i>V</i><sub>OC</sub>âlight intensity dependence measurements and Kelvin probe force microscopy reveal that the DB device configuration is particularly advantageous, if compared to the conventional BHJ, because it enables optimization of the donor and acceptor layers independently to minimize the effect of trapping and to fully exploit the improved transport properties
Dynamic Microscopy Study of Ultrafast Charge Transfer in a Hybrid P3HT/Hyperbranched CdSe Nanoparticle Blend for Photovoltaics
We present a spectroscopic investigation on a new hyperbranched cadmium selenide nanocrystals (CdSe NC)/polyÂ(3-hexylthiophene) (P3HT) blend, a potentially good active component in hybrid photovoltaics. Combined ultrafast transient absorption spectroscopy and morphological investigations by means of an ultrafast confocal microscope reveal a strong influence of the complex local structure on the photogenerated carrier dynamics. In particular, we map the electron-transfer process across the hybrid NC/polymer interface, and we reveal that charge separation occurs through a preferential pathway from the CdSe nanobranches to the P3HT chains. Efficient charge generation at the distributed heterojunction is also confirmed by scanning kelvin probe force microscopy measurements
Synthesis and Photovoltaic Properties of Regioregular Head-to-Head Substituted Thiophene Hexadecamers
We describe the expedient synthesis of regioregular thiophene
hexadecamers
head-to-head (hh) substituted with hexyl and hexylthio grous. The
synthesis was carried out by means of a sequence of ultrasound-assisted
selective monobrominations and microwave-assisted Suzuki reactions
using 4,4,5,5-tetramethyl-1,3,2-dioxaborolane in THF:water. The hexadecamers,
which are very soluble in organic solvents, were investigated in solution
and thin film by a variety of techniques (UV, PL, CV, X-ray diffraction,
FET charge mobility, SKFM) with the aim of elucidating the effect
of the sulfur spacer on morphology and functional properties. We show
that the sulfur spacer compensates for the decrease in ĎâĎ
conjugation caused by the hh regiochemistry and that the Îť<sub>max</sub> value and redox potentials of the S-alkyl-substituted hexadecamer
are similar to those of head-to-tail substituted polyÂ(3-hexylthiophene).
Measurements in field effect transistor devices showed that the alkylthio-substituted
hexadecamer is a p-type semiconductor while the alkyl-substituted
counterpart in the same conditions is not electroactive. Scanning
Kelvin force microscopy measurements showed that a blend of the alkylthio-substituted
hexadecamer with PCBM displays photovoltaic behavior under illumination.
In agreement with this, a bulk heterojunction cell fabricated employing
the same blend displayed near 1.5% conversion efficiency without addition
of additives or device optimization
Nanoscale Characterization and Unexpected Photovoltaic Behavior of Low Band Gap Sulfur-Overrich-Thiophene/Benzothiadiazole Decamers and Polymers
Highly
soluble air-stable conjugated decamers and polymers (compounds <b>1</b>â<b>6</b>) with alternating âsulfur-overrichâ
bisÂ(3,4â˛-<i>S</i>-alkyl)-2,2â˛-bithiophenes
as the donor units and 2,1,3-benzothiadiazoles as the acceptor units
were designed and expediently synthesized with the aid of microwave
and ultrasound enabling technologies. Solid-state cyclovoltammetry
showed that <b>1</b>â<b>6</b> had oxidation and
reduction potentials in the range 0.6â0.9 V and â1/â1.2
V (vs SCE), respectively, with energy gaps below 2 eV. The electronic
properties of spin-coated films of pure <b>1</b>â<b>6</b> were investigated with nanoscale resolution by Kelvin probe
force microscopy (KPFM). KPFM measurements showed that charge generation
and separation were obtained for all films under illumination. Consequently, <b>1</b>â<b>6</b> were tested on single-material organic
solar cells (SMOCs). In agreement with KPFM results, photovoltaic
behavior was observed for all compounds with power conversion efficiencies
in line with the best results obtained so far for the few donorâacceptor
molecules already shown to perform in single-component solar cells.
To our knowledge, this is the first time in which thiopheneâbenzothiadiazole
co-oligomers and copolymers are shown to be photoactive materials
in SMOCs