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Understanding the underlying physics of charge transport in organic semiconductors under illumination is important for the development of novel optoelectronic applications. We study the effects of monochromatic light in the visible spectrum on the channel of an organic thin-film transistor based on 2,8-difluoro-5,11-bis(triethylsilylethynyl) anthradithiophene. When the channel of the transistor was illuminated with red, green, or blue light, more charge carriers were measured than what exciton generation from photon absorption alone could provide, leading to a photon-to-charge-carrier conversion efficiency much larger than 100%. We explain this phenomenon using a model incorporating space-charge limited photocharges and enhanced hole injection from the source electrode due to lowering of the potential barrier by photogenerated electrons. 

Abstract Organic semiconductors enable low‐cost solution processing of optoelectronic devices on flexible substrates. Their use in contemporary applications, however, is sparse due to persistent challenges in achieving the requisite performance levels in a reliable and reproducible manner. A critical bottleneck is the inefficiency associated with charge injection. Here, large‐scale simulations are employed to identify operational windows where key device parameters that are difficult to control experimentally, such as the contact resistance, become less consequential to overall device functionality. This design methodology overcomes injection barrier limitations in organic field‐effect transistors (OFETs), leading to high charge carrier mobility and significantly expanding the range of suitable electrode materials. Leveraging this new understanding, all‐organic, solution‐deposited OFETs are successfully fabricated on flexible substrates. These devices incorporate printed contacts and showcase mobilities exceeding 5 cm² Vs⁻¹. These results provide a route for accessing the fundamental limits of material properties even in the absence of ideal contacts – a critical step in establishing reliable structure/property relationships and optimal material design paradigms. While reducing the injection barrier and contact resistance remains critical for achieving high OFET performance, this work demonstrates a path toward consistently achieving high charge carrier mobility through device geometry design, ultimately reducing processing complexity and cost. 

Abstract Perovskite optoelectronics are regarded as a disruptive technology, but their susceptibility to environmental degradation and reliance on toxic solvents in traditional processing methods pose significant challenges to their practical implementation. Herein, methylammonium lead iodide (MAPbI₃) perovskite films processed via a solvent‐free laser printing technique, that exhibit exceptional stability, are reported. These films withstand extreme conditions, including high doses of X‐ray radiation exceeding 200 Gy, blue laser illumination, 90% relative humidity, and thermal stress up to 80 °C for over 300 min in air. We demonstrate that laser‐printed films maintain their structural integrity and optoelectronic properties even after prolonged exposure to these stressors, significantly surpassing the stability of conventionally processed films. The enhanced stability is attributed to the unique film formation mechanism and resulting defect‐tolerant microstructure. These results underscore the potential of laser printing as a scalable, safe, and sustainable manufacturing route for producing stable perovskite‐based devices with potential applications in diverse fields, ranging from renewable energy to large‐area electronics and space exploration. 

Charge-transfer (CT) complexes are a promising class of materials for the semiconductor industry because of their versatile properties. This class of compounds shows a variety of phase transitions, which are of interest because of their potential impact on the electronic characteristics. Here temperature-dependent vibrational spectroscopy is used to study structural phase transitions in a set of organic CT complexes. Splitting and broadening of infrared-active phonons in the complex formed between pyrene and pyromellitic dianhydride (PMDA) confirm the structural transition is of the order-disorder type and complement previous x-ray diffraction (XRD) results. We show that this technique is a powerful tool to characterize transitions, and apply it to a range of binary CT complexes composed of polyaromatic hyrdocarbons (anthracene, perylene, phenanthrene, pyrene, and stilbene) and PMDA. We extend the understanding of transitions in perylene-PMDA and pyrene-PMDA, and show that there are no order-disorder transitions present in anthracene-PMDA, stilbene-PMDA and phenanthrene-PMDA in the temperature range investigated here. 

Abstract Field‐effect transistors (FETs) are key elements in modern electronics and hence are attracting immense scientific and commercial attention. The recent emergence of metal halide perovskite materials and their tremendous success in the field of photovoltaics have triggered the exploration of their application in other (opto)electronic devices, including FETs and phototransistors. In this review, the current status of the field is discussed, the challenges are highlighted, and an outlook for the future perspectives of perovskite FETs is provided. First, attention is drawn to the device physics and the fundamental processes that influence these devices, including the role of ion migration and defects, effects of temperature, light, and measurement conditions. Next, the performance of perovskite transistors and phototransistors reported to date are surveyed and critically assessed. Finally, the key challenges that impede perovskite transistor progress are outlined and discussed. The insights gained from the study of other perovskite optoelectronic devices may be adopted to address these challenges and advance this exciting field of research closer to the industrial application are examined. 

Abstract Conjugated polymers have gained momentum as serious contenders for next‐generation flexible electronics, but their susceptibility to water represents a major problem. Atmospheric water is ubiquitous and its inadvertent diffusion into polymeric devices generates charge carrier traps, reducing their performance and stability. A good understanding of the physical processes associated with the presence of water is therefore necessary in order to be able to suppress the related trapping events and enable stable, high‐performance devices. Here, evidence is shown that water introduces traps in the bandgap of organic semiconductors and the impact of these traps on the electrical properties of polymer organic field‐effect transistors (OFETs) based on indacenodithiophene‐co‐benzothiadiazole (IDT‐BT) is investigated. Monitoring device parameters and the trap density of states (t‐DOS) during moisture extrication reveals the existence of two types of water‐related traps: shallow traps originating from water inhabiting the voids of the polymer film and deeper traps arising from chemisorbed water present at the dielectric/polymer interface. A trap passivation method based on flame‐annealing is introduced to eliminate the interfacial traps. As a result, stable OFETs, with threshold voltage shifts less than ΔV_th = −0.3 V and constant mobilities (<10% variation) after three months of storage, are fabricated. 

Abstract Organic semiconductors have sparked interest as flexible, solution processable, and chemically tunable electronic materials. Improvements in charge carrier mobility put organic semiconductors in a competitive position for incorporation in a variety of (opto‐)electronic applications. One example is the organic field‐effect transistor (OFET), which is the fundamental building block of many applications based on organic semiconductors. While the semiconductor performance improvements opened up the possibilities for applying organic materials as active components in fast switching electrical devices, the ability to make good electrical contact hinders further development of deployable electronics. Additionally, inefficient contacts represent serious bottlenecks in identifying new electronic materials by inhibiting access to their intrinsic properties or providing misleading information. Recent work focused on the relationships of contact resistance with device architecture, applied voltage, metal and dielectric interfaces, has led to a steady reduction in contact resistance in OFETs. While impressive progress was made, contact resistance is still above the limits necessary to drive devices at the speed required for many active electronic components. Here, the origins of contact resistance and recent improvement in organic transistors are presented, with emphasis on the electric field and geometric considerations of charge injection in OFETs. 

Abstract Radiation therapy is one of the most prevalent procedures for cancer treatment, but the risks of malignancies induced by peripheral beam in healthy tissues surrounding the target is high. Therefore, being able to accurately measure the exposure dose is a critical aspect of patient care. Here a radiation detector based on an organic field‐effect transistor (RAD‐OFET) is introduced, an in vivo dosimeter that can be placed directly on a patient's skin to validate in real time the dose being delivered and ensure that for nearby regions an acceptable level of low dose is being received. This device reduces the errors faced by current technologies in approximating the dose profile in a patient's body, is sensitive for doses relevant to radiation treatment procedures, and robust when incorporated into conformal large‐area electronics. A model is proposed to describe the operation of RAD‐OFETs, based on the interplay between charge photogeneration and trapping. 

Abstract Solution‐processable organic semiconductors can serve as the basis for new products including rollable displays, tattoo‐like smart bandages for real‐time health monitoring, and conformable electronics integrated into clothing or even implanted in the human body. For such exciting commercial applications to become a reality, good device performance and uniformity over large areas are necessary. The design of new materials has progressed at an astonishing pace, but accessing their intrinsic, efficient electrical properties in large‐area flexible device arrays is difficult. The development of protocols that allow integration with industrial‐scale processing for high‐throughput manufacturing, without the need to compromise on performance, is the key for transitioning these materials to real‐life applications. In this work, large‐area arrays of organic thin‐film transistors obtained by spray‐coating the high‐mobility polymer indacenodithiophene‐co‐benzothiadiazole (IDTBT) are demonstrated. A maximum charge carrier mobility of 2.3 cm²V⁻¹s⁻¹, with a very narrow performance distribution, is obtained over surface areas of 10 cm × 10 cm. The devices retain their electrical properties when bent multiple times and at different curvatures. In addition, large arrays of highly sensitive (0.25% change in mobility for 1% humidity variation), reusable, near‐identical humidity sensors are produced in a one‐step fabrication and calibrated from 0% to 94% relative humidity. 

Abstract The crystal structures of the charge‐transfer (CT) cocrystals formed by the π‐electron acceptor 1,3,4,5,7,8‐hexafluoro‐11,11,12,12‐tetracyanonaphtho‐2,6‐quinodimethane (F₆TNAP) with the planar π‐electron‐donor molecules triphenylene (TP), benzo[b]benzo[4,5]thieno[2,3‐d]thiophene (BTBT), benzo[1,2‐b:4,5‐b′]dithiophene (BDT), pyrene (PY), anthracene (ANT), and carbazole (CBZ) have been determined using single‐crystal X‐ray diffraction (SCXRD), along with those of two polymorphs of F₆TNAP. All six cocrystals exhibit 1:1 donor/acceptor stoichiometry and adopt mixed‐stacking motifs. Cocrystals based on BTBT and CBZ π‐electron donor molecules exhibit brickwork packing, while the other four CT cocrystals show herringbone‐type crystal packing. Infrared spectroscopy, molecular geometries determined by SCXRD, and electronic structure calculations indicate that the extent of ground‐state CT in each cocrystal is small. Density functional theory calculations predict large conduction bandwidths and, consequently, low effective masses for electrons for all six CT cocrystals, while the TP‐, BDT‐, and PY‐based cocrystals are also predicted to have large valence bandwidths and low effective masses for holes. Charge‐carrier mobility values are obtained from space‐charge limited current (SCLC) measurements and field‐effect transistor measurements, with values exceeding 1 cm²V⁻¹s¹being estimated from SCLC measurements for BTBT:F₆TNAP and CBZ:F₆TNAP cocrystals.