Organic semiconductors require an energetic offset in order to photogenerate free charge carriers efficiently, owing to their inability to effectively screen charges. This is vitally important in ...order to achieve high power conversion efficiencies in organic solar cells. Early heterojunction‐based solar cells were limited to relatively modest efficiencies (<4%) owing to limitations such as poor exciton dissociation, limited photon harvesting, and high recombination losses. The development of the bulk heterojunction (BHJ) has significantly overcome these issues, resulting in dramatic improvements in organic photovoltaic performance, now exceeding 18% power conversion efficiencies. Here, the design and engineering strategies used to develop the optimal bulk heterojunction for solar‐cell, photodetector, and photocatalytic applications are discussed. Additionally, the thermodynamic driving forces in the creation and stability of the bulk heterojunction are presented, along with underlying photophysics in these blends. Finally, new opportunities to apply the knowledge accrued from BHJ solar cells to generate free charges for use in promising new applications are discussed.
The development of the bulk heterojunction, in terms of materials design, device engineering, and the underpinning physical understanding, has led to significant improvements in organic photovoltaics. Looking forward, the bulk heterojunction concept is likely to allow even greater solar cell efficiencies and interestingly, can be applied to other organic electronic applications, such as organic photodetectors and photocatalysts.
This progress report summarizes the numerous DPP‐containing polymers recently developed for field‐effect transistor applications including diphenyl‐DPP and dithienyl‐DPP‐based polymers as the most ...commonly reported materials, but also difuranyl‐DPP, diselenophenyl‐DPP and dithienothienyl‐DPP‐containing polymers. We discuss the hole and electron mobilities that were reported in relation to structural properties such as alkyl substitution patterns, polymer molecular weights and solid state packing, as well as electronic properties including HOMO and LUMO energy levels. We moreover consider important aspects of ambipolar charge transport and highlight fundamental structure‐property relations such as the relationships between the thin film morphologies and the charge carrier mobilities observed for DPP‐containing polymers.
In this Progress Report, the most recent literature on diketopyrrolopyrrole‐containing polymers developed for field‐effect transistor applications is reviewed and the structure–property relations of importance for achieving high performance n‐ and p‐type transistor materials are discussed in detail.
In this review, we describe and discuss recent advances in the performance of polymeric semiconductors in organic field effect transistors (OFETs). Design concepts such as short intermolecular ...contacts, low conformational disorder, side chain optimization, and noncovalent interactions have all been successfully employed to improve the charge carrier mobility of polymer thin films. The relationship between the molecular design, thin film microstructure, and electrical performance has been exemplified by a range of thiophene, bridged and fused ring, diketopyrrolopyrrole (DPP), and isoindigo containing polymers which are reviewed and discussed.
Ternary organic solar cells (TSCs) contain a single three-component photoactive layer with a wide absorption window, which is obtained without the need for multiple stacks. Subsequently, TSCs have ...attracted great interest in the photovoltaics field. Through careful selection of the three (or more) active components that form the photoactive layer, all photovoltaic parameters can be simultaneously enhanced within a TSC — a strategy that has resulted in record efficiencies for single-junction solar cells. In this Review, we outline key developments in TSCs, with a focus on the central role of the third component in achieving record efficiencies. We analyse the effects of the third component on the nanomorphology of the bulk heterojunction and the photovoltaic parameters of TSCs. Moreover, we discuss the charge-transfer and/or energy-transfer mechanisms and nanomorphology models that govern the operation of TSCs. We consider both polymer and small-molecule donors as well as fullerenes and recently developed non-fullerene acceptors. In addition, we summarize the recent success of TSCs in mitigating the stability issues of binary solar cells. Finally, we provide a perspective on the advantages of ternary blends and suggest design strategies for highly efficient and stable devices for commercial photovoltaics.Adding a third component into a binary blend is a promising strategy for simultaneously improving all photovoltaic parameters in organic solar cells. In this Review, we discuss the role of the third component in influencing the energetics, charge-carrier recombination and stability in ternary solar cells.
Organic semiconductors are solution-processable, lightweight and flexible and are increasingly being used as the active layer in a wide range of new technologies. The versatility of synthetic organic ...chemistry enables the materials to be tuned such that they can be incorporated into biological sensors, wearable electronics, photovoltaics and flexible displays. These devices can be improved by improving their material components, not only by developing the synthetic chemistry but also by improving the analytical and computational techniques that enable us to understand the factors that govern material properties. Judicious molecular design provides control of the semiconductor frontier molecular orbital energy distribution and guides the hierarchical assembly of organic semiconductors into functional films where we can manipulate the properties and motion of charges and excited states. This Review describes how molecular design plays an integral role in developing organic semiconductors for electronic devices in present and emerging technologies.
Organic solar cells now exceed 10% efficiency igniting interest not only in the fundamental molecular design of the photoactive semiconducting materials, but also in overlapping fields such as green ...chemistry, large-scale processing and thin film stability. For these devices to be commercially useful, they must have lifetimes in excess of 10 years. One source of potential instability, is that the two bicontinuous phases of electron donor and acceptor materials in the photoactive thin film bulk heterojunction, change in dimensions over time. Photocrosslinking of the π-conjugated semiconducting donor polymers allows the thin film morphology to be ‘locked’ affording patterned and stable blends with suppressed fullerene acceptor crystallization. This article reviews the performance of crosslinkable polymers, fullerenes and additives used to-date, identifying the most promising.
Electronically interfacing with the nervous system for the purposes of health diagnostics and therapy, sports performance monitoring, or device control has been a subject of intense academic and ...industrial research for decades. This trend has only increased in recent years, with numerous high-profile research initiatives and commercial endeavors. An important research theme has emerged as a result, which is the incorporation of semiconducting polymers in various devices that communicate with the nervous systemfrom wearable brain-monitoring caps to penetrating implantable microelectrodes. This has been driven by the potential of this broad class of materials to improve the electrical and mechanical properties of the tissue–device interface, along with possibilities for increased biocompatibility. In this review we first begin with a tutorial on neural interfacing, by reviewing the basics of nervous system function, device physics, and neuroelectrophysiological techniques and their demands, and finally we give a brief perspective on how material improvements can address current deficiencies in this system. The second part is a detailed review of past work on semiconducting polymers, covering electrical properties, structure, synthesis, and processing.
Over the past three decades, significant research efforts have focused on improving the charge carrier mobility of organic thin‐film transistors (OTFTs). In recent years, a commonly observed ...nonlinearity in OTFT current–voltage characteristics, known as the “kink” or “double slope,” has led to widespread mobility overestimations, contaminating the relevant literature. Here, published data from the past 30 years is reviewed to uncover the extent of the field‐effect mobility hype and identify the progress that has actually been achieved in the field of OTFTs. Present carrier‐mobility‐related challenges are identified, finding that reliable hole and electron mobility values of 20 and 10 cm2 V−1 s−1, respectively, have yet to be achieved. Based on the analysis, the literature is then reviewed to summarize the concepts behind the success of high‐performance p‐type polymers, along with the latest understanding of the design criteria that will enable further mobility enhancement in n‐type polymers and small molecules, and the reasons why high carrier mobility values have been consistently produced from small molecule/polymer blend semiconductors. Overall, this review brings together important information that aids reliable OTFT data analysis, while providing guidelines for the development of next‐generation organic semiconductors.
Overestimated carrier mobility values reported in recent years for organic thin‐film transistors (OTFTs) have contaminated the literature. 30 years of OTFT carrier mobility data is examined in an effort to identify actual progress achieved, and summarize the key design strategies behind high carrier mobility values for both p‐ and n‐type organic semiconductors.
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