Impact of n-Doping Mechanisms on the Molecular Packing and Electron Mobilities of Molecular Semiconductors for Organic Thermoelectrics

Electrical conductivity is one of the key parameters for organic thermoelectrics and depends on both the concentration and mobility of charge carriers. To increase the carrier concentration, molecular dopants have to be added into organic semiconductor materials, whereas the introduction of dopants can influence the molecular packing structures and hence carrier mobility of the organic semiconductors. Herein, we have theoretically investigated the impact of different n-doping mechanisms on molecular packing and electron transport properties by taking N-DMBI-H and Q-DCM-DPPTT respectively as representative n-dopant and molecular semiconductor. The results show that when the doping reactions and charge transfer spontaneously occur in the solution at room temperature, the oppositely charged dopant and semiconductor molecules will be tightly bound to disrupt the semiconductor to form long-range molecular packing, leading to a substantial decrease of electron mobility in the doped film. In contrast, when the doping reactions and charge transfer are activated by heating the doped film, the molecular packing of the semiconductor is slight affected and hence the electron mobility remains quite high. This work indicates that thermally-activated n-doping is an effective way to achieve both high carrier concentration and high electron mobility in n-type organic thermoelectric materials.

Methylthiophene terminated D-π-D molecular semiconductor as multifunctional interfacial material for high performance perovskite solar cells

Rational modulating the physicochemical properties at perovskite-charge transporting layer interface is crucial for further performance improvement of metal halide perovskite solar cells (PSCs). Here, we present two methylthiophene terminated molecular...

Controlled Aggregation of Peptide Substituted Perylene-Bisimides

<p>In recent years there has been an intersection of supramolecular chemistry and materials science, with a particular focus on the controlled self-assembly of functional building blocks. The impetus for assembly of organised architectures is a requirement due to organic electronic device performance being sensitive to the geometric configuration of adjacent molecular semiconductors, interacting by means of overlapping π-orbitals to create electronic conduction. Inspired by the formation of elegant supramolecular structures in nature, this work employs perylene bisimides coupled to synthetic peptides which are able to control the assembly of chromophores in solution. Through examining the perturbations of optical absorption and fluorescence spectroscopic signatures, the presence of aggregates, and also the geometric configurations of adjacent chromophores are determined. By exploring these features as a function of peptide design, pH, solvent composition, and ionic strength, it is demonstrated that aggregation is strongly induced by the peptide and the aromatic core, with significant dependence on the electrostatic repulsion between peptide segments. By manipulating solvent compositions, we demonstrate the ability to induce controlled reorganisation of aggregates through the introduction of charge onto the peptide sequence in high water concentration solution. Furthermore, application of the exciton model to absorption spectra establishes the tuneability of aggregates by specific ion binding between neighbouring peptides. Our results demonstrate the capability of peptide sequences to drive aggregation of molecular semiconductor building blocks; moreover, the peptides allow fine tuning of the electronic overlap between neighbouring building blocks. The proof of concept paves the way for further investigation into utilising this assembly control for device fabrication, in particular, we see this work being applicable to biosensor devices.</p>

Controlled Aggregation of Peptide Substituted Perylene-Bisimides

<p>In recent years there has been an intersection of supramolecular chemistry and materials science, with a particular focus on the controlled self-assembly of functional building blocks. The impetus for assembly of organised architectures is a requirement due to organic electronic device performance being sensitive to the geometric configuration of adjacent molecular semiconductors, interacting by means of overlapping π-orbitals to create electronic conduction. Inspired by the formation of elegant supramolecular structures in nature, this work employs perylene bisimides coupled to synthetic peptides which are able to control the assembly of chromophores in solution. Through examining the perturbations of optical absorption and fluorescence spectroscopic signatures, the presence of aggregates, and also the geometric configurations of adjacent chromophores are determined. By exploring these features as a function of peptide design, pH, solvent composition, and ionic strength, it is demonstrated that aggregation is strongly induced by the peptide and the aromatic core, with significant dependence on the electrostatic repulsion between peptide segments. By manipulating solvent compositions, we demonstrate the ability to induce controlled reorganisation of aggregates through the introduction of charge onto the peptide sequence in high water concentration solution. Furthermore, application of the exciton model to absorption spectra establishes the tuneability of aggregates by specific ion binding between neighbouring peptides. Our results demonstrate the capability of peptide sequences to drive aggregation of molecular semiconductor building blocks; moreover, the peptides allow fine tuning of the electronic overlap between neighbouring building blocks. The proof of concept paves the way for further investigation into utilising this assembly control for device fabrication, in particular, we see this work being applicable to biosensor devices.</p>

Investigation on Film Quality and Photophysical Properties of Narrow Bandgap Molecular Semiconductor Thin Film and Its Solar Cell Application

Hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5) is one of the narrowest bandgap molecular semiconductor reported in recent years. Through the study of its energy band structure, it can be identified as an N-type semiconductor and is able to absorb most of the visible light, making it suitable to fabricate solar cells. In this paper, SnO2 was used as an electron transport layer in HDA-BiI5-based solar cells, for its higher carrier mobility compared with TiO2, which is the electron transport layer used in previous researches. In addition, the dilution ratio of SnO2 solution has an effect on both the morphology and photophysical properties of HDA-BiI5 films. At the dilution ratio of SnO2:H2O = 3:8, the HDA-BiI5 film has a better morphology and is less defect inside, and the corresponding device exhibited the best photovoltaic performance.

Photodetector without Electron Transport Layer Based on Hexane-1,6-Diammonium Pentaiodobismuth (HDA-BiI5) Molecular Semiconductor

With the development of the semiconductor industry, research on photoelectronic devices has been emphasized. In this paper, a molecular semiconductor material with a narrow bandgap of hexane-1,6-diammonium pentaiodobismuth (HDA-BiI5) was utilized to prepare photodetectors without electron transport layers. Using a single light source, the effects of different wavelengths and different powers on the photoresponsivity, switching ratio, specific detectivity, and external quantum efficiency of the device were investigated. It is demonstrated that this device has excellent responsivity, specific detectivity, stability, and repeatability, and this work will help expand the application of molecular semiconductor materials for photodetection.