Direct Correlation Between Electric and Structural Properties During Solidification of Poly(3-hexylthiophene) Drop-Cast Films

In Situ Coupling Applied Voltage and Synchrotron Radiation: Operando Characterization of Transistors

A compact voltage application setup has been developed for in situ electrical testing of organic field effect transistors in combination with X-ray scattering studies at a synchrotron beamlines. Challenges faced during real condition in-operando test of newly developed OFETs originated an idea of creation of a new setup which excludes number of factors that make experiments complicated. The application of the setup is demonstrated on a prototype of an organic transistors based on α,ω-dihexyl-α-quaterthiophene molecules. The new setup allows to monitor material structural changes by X-ray scattering under applied voltage conditions and their direct correlations. The versatile setup eliminates possible shadowing effects and short circuits due to misalignment of the contacts. The electrical stability of the prototypes was characterized by the application of different voltage values. Corresponding structural changes were monitored by grazing X-ray scattering technique before, during and after the voltage was applied. The selected oligothiophene material with proved transistor properties shows high stability and directional anisotropy under applied voltage conditions. Thanks to a compact and flexible design of the setup, different type of small dimension devices could be studied under external voltage conditions at various synchrotron beamlines.

Local scale structural changes of working OFET devices

We present an in situ nanobeam grazing-incidence X-ray diffraction (nanoGIXD) study of real-sized organic field effect transistors (OFET) under applied voltage. The nano-sized beam allows for spatially resolved monitoring of the structural behavior across the poly(3-hexylthiophene) (P3HT) polymer channel and the interfacial regions of the source and drain gold electrodes before and after the operation cycle. We observe major alterations of the gold contacts, in particular diffusion of Au atoms into the polymer channel and a local reorientation of the recrystallized Au nanocrystallites quantified by Hermans' orientation factors. Therefore, the initially sharp electrode-polymer interfaces are significantly modified as a result of device operation. Our findings demonstrate that nanoGIXD has a high potential to probe functionality and reliability of working organic devices.

Phase Transitions and Formation of a Monolayer-Type Structure in Thin Oligothiophene Films: Exploration with a Combined In Situ X-ray Diffraction and Electrical Measurements

A combination of in situ electrical and grazing-incidence X-ray diffraction (GIXD) is a powerful tool for studies of correlations between the microstructure and charge transport in thin organic films. The information provided by such experimental approach can help optimizing the performance of the films as active layers of organic electronic devices. In this work, such combination of techniques was used to investigate the phase transitions in vacuum-deposited thin films of a common organic semiconductor dihexyl-quarterthiophene (DH4T). A transition from the initial highly crystalline phase to a mesophase was detected upon heating, while only a partial backward transition was observed upon cooling to room temperature. In situ electrical conductivity measurements revealed the impact of both transitions on charge transport. This is partly accounted for by the fact that the initial crystalline phase is characterized by inclination of molecules in the plane perpendicular to the π-π stacking direction, whereas the mesophase is built of molecules tilted in the direction of π-π stacking. Importantly, in addition to the two phases of DH4T characteristic of the bulk, a third interfacial substrate-stabilized monolayer-type phase was observed. The existence of such interfacial structure can have important implications for the charge mobility, being especially favorable for lateral two-dimensional charge transport in the organic field-effect transistors geometry.

Impact of the solubility of organic semiconductors for solution-processable electronics on the structure formation: a real-time study of morphology and electrical properties

The control of structure formation in the active layers of organic solar cells allows for improvement in their processability and enhancement of the efficiency of the final devices. In the present work, in situ studies of film formation from binary toluene solutions of an electron donor, poly(3-hexylthiophene) (P3HT), and an electron acceptor such as [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) or indene-C60 bisadduct (ICBA) have been conducted. These experiments were carried out using GIWAXS with simultaneous electric current measurements. The comparative analysis of the intensity of the amorphous halo, and the 100 and 020 peaks of P3HT reveals the development of the semicrystalline morphology of the donor through a partly-ordered phase. The experiments show the impact of the chemical structure of the acceptor, as well as that of the donor : acceptor ratio on the kinetics of drying and crystallization. The optimal bulk heterojunction morphology was achieved for P3HT : ICBA 1 : 1, which exhibited the highest value of current. A more efficient phase separation in non-annealed P3HT:ICBA films as compared to P3HT:PCBM was accounted for by the differences in solubility of the components in toluene. The structure formation during solvent evaporation can be subdivided into three stages, including the ordering of the polymer in solution, phase separation during precipitation, and the perfectioning of P3HT crystals in the dry film.

Synthesis, nanostructure evaluation and tunable anomalous 3D hopping transport of manganese ferrite encapsulated poly[3,4-(ethylenedioxy)thiophene] decorated graphene layer

A straightforward novel synthetic approach of manganese ferrite encapsulated poly[3,4-(ethylenedioxy)thiophene] nanocomposite decorated on a graphene layer (NIPG) is engineered assisted by dodecyl benzene sulphonic acid as surfactant.

Real time studies of thiophene-based conjugated oligomer solidification

Real time investigations of a solidification process of thiophene based oligomer system by simultaneous probing of the structure and the electrical response.