During last decades, organic conjugated material-based devices demonstrate huge potential for new generation of low-cost electronics. Late reviews report on of the semiconducting organic materials of different composition with outstanding electrical and optical properties for applications as functional materials in organic light emitting diodes [1], organic filed-effect transistors (OFETs) [2–4] or organic solar cells [5, 6].
Important role in the studies, before application in mass production, is playing a strong connection between investigated material properties and its microstructure and molecular ordering. Molecule with similar components but with different structure, ordering, distribution, and various bents might demonstrate very different properties and reaction to externally applied conditions [7, 8]. Rather recent studies shown relevance of the static and dynamic parameters in the electrical performances of OFETs, and showed that the radiofrequency model established in a solid-state, it allows a reliable prediction of the performances of organic prototype. Authors are reporting on the effective miniaturization of OFETs, which is expected to provide a useful design guideline also in the integration of organic digital and analog circuits. [9]. A lower limit of the mobility of ‘high-performance’ organic transistors has been established in the range of 1–10 cm2 V− 1 s− 1 [10]. However, this limit could be reach by rather short list of the organic materials such as single crystals or highly ordered films. Small molecules including oligothiophenes are promising candidates for organic electronics applications with mobilities up to 1 cm2 V− 1 s− 1 [11] and power conversion efficiency reaching of 10% [12]. Among different linear oligothiophenes α,α’-dihexyl-quaterthiophene (DH4T) is well-known oligothiophenes revealing high field-effect mobility and well-ordered microstructure [13, 14]. In particular, a highly crystalline phase of DH4T with in-plane π-π orientation is beneficial for charge transport [15].
The unique properties of organic semiconductors, issues and problems being non-typical for inorganic transistors are described in [13]. Important place in this research is taken by in-situ experiments, in particular by in-situ investigation using X-ray diffraction and scattering techniques [16–18]. Since most of the smart devices are designed as layered systems on substrate including electrodes and deposited organic material, an instrument sensitive to surfaces and interfaces is necessary. The technique of grazing X-ray scattering/diffraction with controllable penetration depth is well-established for characterization of organic semiconductors and their properties. Grazing incidence small and wide angle scattering (GISAXS, GIWAXS) as well as grazing incidence X-ray diffraction (GIXD) are widely used methods for functional layers characterization of organic electronics device prototypes [19]. Benefits of the technique already have been demonstrated in various studies of the material structure for organic electronics. In-situ investigations of organic transistors were performed and reported based on absorption spectroscopy [20, 21], X-ray diffraction experiments [22, 23] or combination of both [4]. A structural stability of 5,5′-bis(naphth-2-yl)-2,2′-bithiophene (NaT2) based OFETs was studied during operando experiment in combination with GIXD technique. A device with 500 µm long channel was tested by submillimeter X-ray beam. Rather detail analysis of the material structure demonstrated a high structural stability with variation of 1% in range of up to 40V [24]. Strong contribution to pentacene based OFETs was demonstrated from another operando experiment combing with X-ray diffraction [25]. In this work nanometer sized monolayers system response on external applied voltage was monitored by XRD. The studies demonstrated slight tilt and reorganization of the molecules at grain boundaries, under applied voltage molecules forming highly crystalline and textured crystal domains.
The structural evolution of the polymer: fullerene active layers during the drying process gives insight of the microstructure formation linked to the optimization of the solar cells [26]. Moreover, the solution processing and the microstructure formation can be coupled with electrical response of the active layers [27, 28]. Usually scattering X-ray signal is rather weak in solution phase and at the initial stage of the microstructure formation and such studies would be impossible to realize without usage of synchrotron radiation.
Furthermore, the synchrotron beam focused to submicron or smaller size becomes a necessary tool to achieve a sufficiently high spatial resolution and strong enough signal to monitor microstructural changes during the instrument operation. Typical synchrotron beamlines that deliver a nanometer beam are very spatially limited, what requires from the experimental setup to be compact and flexible. During such investigations one should consider a number of limiting factors, except abovementioned, which are radiation damage, complicity of contacts alignment, small size of the systems. Importance and complicity of operando synchrotron measurements with nanosize beam were shown in [7] where potential of nanoGIXD experiment was used for a study of real-sized organic field effect transistors under applied voltage.
However, there is no routine way for detailed studies of the material behavior under real working conditions. Particular difficulties are related to the small dimensions of the active layers of the modern smart devices and circuits.
In this paper, we present a self-developed setup for in-situ studies under applied voltage, which is compact and compatible with different synchrotron beamlines. The Voltage in-situ setup for Application at Synchrotron beamlines (VINAS) is a new tool dedicated for operando studies of the multilayer based system that supposed to be operated under external voltage conditions. A self-explanatory and easy-to-use setup simplifies the electrical connection and eliminates any blocking of an X-ray beam. VINAS can be operated under broad ranges of applied voltages, which make the setup helpful for studies of almost all types of new vertical microelectronic devices. The potential of the setup is demonstrated on operando studies of working prototype OFET device based on DH4T oligothiophene. Results obtained during the reported experiment complete the knowledge of the device stability under externally control experimental conditions.