Controlled Pinning of Conjugated Polymer Spherulites and Its Application in Detectors

Abstract

is of great interest because of their impact on mechanical, and functional properties, including thermal conductivity, [1] charge carrier mobility, [2][3][4][5][6][7] and electrical conductivity. [8,9] In addition, for suitable macroscopic polymer chain arrangements, polarized absorption and emission can be observed. [10] As a consequence, a variety of methods have been developed to manipulate and control the microstructure and the orientation of conjugated polymers. [11] Some of these methods result in spherulites, densely branched, polycrystalline regions of material with spherically, or in 2 dimensions circularly, radiating fibers. [12,13] Because of their circular shape, which contains all possible fiber orientations in the plane, spherulites are an attractive system to probe orientation-dependent electrical and optical properties. Conventional deposition techniques such as spin-and blade-coating usually result in isotropic layers with a random orientation of the crystalline lamellae down to the microscopic scale. This is caused by the immense density of nucleation sites and the resulting uncontrolled growth. Several methods to control the nucleation density have been demonstrated. For example, a careful control of the solvent partial pressure during swelling of an already deposited layer allows redissolving all but a few crystallites, which can then be regrown under controlled conditions to microscopic spherulites. [3,14] Another method, which is experimentally simpler to realize, uses the epitaxial growth of conjugated polymers or small molecules on crystalline 1,3,5-trichlorobenzene (TCB) from the melt, [15] or directly from solution, [16] resulting in larger macroscopic spherulitic structures. In the former, molten TCB acts as solvent for the conjugated system and upon reducing the temperature below the melting point, TCB solidifies, enforcing the epitaxial crystallization of the conjugated system. For the solution process, on the other hand, a given amount of TCB is mixed together with the conjugated component into a carrier solvent such as chlorobenzene (CB). During deposition at room temperature, the wet film dries, increasing the concentration of the solid content in the solution until the solubility limit is reached and the solutes start solidifying. In order to create oriented structures, TCB should crystallize before the polymer or small molecule, which defines a minimum TCB to polymer content (around 4% in volume for a 20 g L −1 P3HT solution in CB). [16] The growth direction of spherulites can be controlled to some extent by patterning the substrate, [17] or by enforcing aThe nucleation of single macroscopic spherulites at desired positions, as well as ordered arrays of multiple spherulites, is demonstrated by combining the use of crystallizable solvents with local control of solvent evaporation during solution deposition. Moreover, the temperature assisted localized frustration of molecular orientation is shown, enabling the fabrication of samples containing both isotropic areas and spherulites....

Panchromatic All‐Polymer Photodetector with Tunable Polarization Sensitivity

“…While the polymers align in the direction of strain, the local polymer order in the film is kept allowing the films to maintain high quantum efficiency. In fact, the photodetector performance in terms of R , detectivity, and 3 dB cutoff frequency is among the highest reported for all‐polymer photodetectors, and intrinsically polarization‐sensitive organic or inorganic photodetectors . In summary, the demonstrated devices highlight the opportunity of all‐polymer photodetectors to achieve high‐performance intrinsically polarization‐sensitive photodetectors with broad spectral response.…”

“…This feature can be exploited to achieve photodetectors that are polarization sensitive without the need of additional light‐manipulating optics. This reduced complexity simplifies polarization‐sensitive devices, and opens up new opportunities in detector architectures such as polarized detectors in tandem to realize compact coincident polarimeters (polarization state detectors) …”

Filterless Polarization‐Sensitive 2D Perovskite Narrowband Photodetectors

“…The former method would increase the cost and complexity of the system similar to the narrowband photodetectors while the latter one relies on the geometric anisotropy of the materials or the anisotropic crystal structures of the materials and thus can reduce the cost and complexity due to the free of polarizer. Filterless polarization‐sensitive photoresponse has demonstrated in a variety of materials including geometric anisotropic materials such as nanowire, nanobelts, and nanotubes and materials with anisotropic crystal structures such as GeAs, SnS, black phosphorus, barium titanium sulfide, and organic semiconductors …”

Semiconducting Polymer Spherulites—From Fundamentals to Polymer Electronics

“…In 2017, they showed that—following the procedure by Müller et al . of adding TCB to the processing solvent—the location of nucleation on the substrate could be controlled by a stream of gas pointing on the film surface, causing the mentioned spot to dry faster and therefore inducing nucleation . For example, by pointing a stream of gas on the substrate surface through a needle during spin coating, a large area covered by only one spherulite could be produced.…”