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Abstract High‐mobility crystalline organic semiconductors are important for applications in advanced organic electronics and photonics. Photogeneration and transport of mobile photocarriers in these materials, although very important, remain underexplored. The photo‐Hall effect can be used to address the fundamental charge transport properties of these functional molecular materials, without the need for fabricating complex transistor devices or chemical doping. Here, a photo‐Hall effect is demonstrated in organic semiconductors, using a benchmark molecular system rubrene as an experimental platform. It is shown that this technique can be used to directly measure the charge carrier mobility and photocarrier density, decouple the surface and bulk transport phenomena, and thus significantly deepen the understanding of the mechanism of photoconductivity in these high‐performance molecular materials. 

Abstract Highly crystalline thin films in organic semiconductors are important for applications in high‐performance organic optoelectronics. Here, the effect of grain boundaries on the Hall effect and charge transport properties of organic transistors based on two exemplary benchmark systems is elucidated: (1) solution‐processed blends of 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene (C₈‐BTBT) small molecule and indacenodithiophene‐benzothiadiazole (C₁₆IDT‐BT) conjugated polymer, and (2) large‐area vacuum evaporated polycrystalline thin films of rubrene (C₄₂H₂₈). It is discovered that, despite the high field‐effect mobilities of up to 6 cm²V⁻¹s⁻¹and the evidence of a delocalized band‐like charge transport, the Hall effect in polycrystalline organic transistors is systematically and significantly underdeveloped, with the carrier coherence factor α < 1 (i.e., yields an underestimated Hall mobility and an overestimated carrier density). A model based on capacitively charged grain boundaries explaining this unusual behavior is described. This work significantly advances the understanding of magneto‐transport properties of organic semiconductor thin films. 

Abstract Utilizing the intrinsic mobility–strain relationship in semiconductors is critical for enabling strain engineering applications in high‐performance flexible electronics. Here, measurements of Hall effect and Raman spectra of an organic semiconductor as a function of uniaxial mechanical strain are reported. This study reveals a very strong, anisotropic, and reversible modulation of the intrinsic (trap‐free) charge carrier mobility of single‐crystal rubrene transistors with strain, showing that the effective mobility of organic circuits can be enhanced by up to 100% with only 1% of compressive strain. Consistently, Raman spectroscopy reveals a systematic shift of the low‐frequency Raman modes of rubrene to higher (lower) frequencies with compressive (tensile) strain, which is indicative of a reduction (enhancement) of thermal molecular disorder in the crystal with strain. This study lays the foundation of the strain engineering in organic electronics and advances the knowledge of the relationship between the carrier mobility, low‐frequency vibrational modes, strain, and molecular disorder in organic semiconductors.