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Many molecular semiconductors show a pronounced polymorphism; i.e. they can adopt different crystal arrangements depending, e.g., on temperature, pressure, and selected solidification pathways. This renders reliable fabrication of molecular semiconductor devices challenging, as minute changes in processing can lead to numerous structures and, hence, optoelectronic responses. Here, we demonstrate using the example of p-DTS(FBTTh2)2 that spatial confinement at the nanoscale can be exploited to detect specific polymorphs and the conditions under they form. A new polymorph exhibiting a higher charge-carrier mobility compared to previously reported p-DTS(FBTTh2)2 crystal forms is found at elevated temperatures and high degree of confinement, illustrating the benefit of our approach and promising that spatial confinement will find wide-spread application to understand and control polymorph formation in organic semiconductors. [ABSTRACT FROM AUTHOR]

Compositional engineering of BiFeO3 can significantly boost its photovoltaic performance. Therefore, controlling site substitution and understanding how it affects the optical and electronic properties while achieving robust and stable phases is essential to continue progressing in this field. Here the influence of cation co-substitution in BiFeO3 on phase purity, optical and electronic properties is investigated by means of X-ray diffraction, spectroscopic ellipsometry and X-ray absorption spectroscopy, respectively. Piezoelectric force microscopy and ferroelectric characterization at room temperature has been carried out in co-doped BiFeO3 films. First-principles calculations are also performed and compared to the experimental observations. It is shown that the incorporation of La3+ in Bi(Fe,Co)O3 films improves phase purity and stability while preserving the reduced band gap achieved in metastable Bi(Fe,Co)O3. Moreover, it is suggested that the changes in the optoelectronic properties are mainly dictated by the hybridisation between unoccupied Co 3d and O 2p states along with the presence of Co3+/Co2+ species. This thorough study on (Bi,La)(Fe,Co)O3 thin films coupled with the use of a cost-effective and facile solution deposition synthesis increases the motivation to continue exploiting the potential of these perovskite materials. [ABSTRACT FROM AUTHOR]

We have developed a one step method for the deposition of uniaxially aligned conjugated polymer layers by directional epitaxial crystallization directly from solution. Oriented, square centimeter sized samples of poly(3-hexylthiophene) (P3HT) deposited from a chlorobenzene (CB) solution containing the additional crystallizable solvent 1,3,5-trichlorobenzene (TCB) are obtained by blade coating. Moreover, we show that the developed technique is not restricted to this specific material combination, but is instead applicable to a range of conjugated polymers and crystallizable solvents. Finally, we demonstrate the potential of this technique by realizing an organic photovoltaic device that exhibits a polarization dependent photoresponse. [ABSTRACT FROM AUTHOR]