An insight into the analogies, state-of-the-art technologies, concepts, and prospects under the umbrella of perovskite materials (both inorganic-organic hybrid halide perovskites and ferroelectric perovskites) for future multifunctional energy conversion and storage devices is provided. Often, these are considered entirely different branches of research; however, considering them simultaneously and holistically can provide several new opportunities. Recent advancements have highlighted the potential of hybrid perovskites for high-efficiency solar cells. The intrinsic polar properties of these materials, including the potential for ferroelectricity, provide additional possibilities for simultaneously exploiting several energy conversion mechanisms such as the piezoelectric, pyroelectric, and thermoelectric effect and electrical energy storage. The presence of these phenomena can support the performance of perovskite solar cells. The energy conversion using these effects (piezo-, pyro-, and thermoelectric effect) can also be enhanced by a change in the light intensity. Thus, there lies a range of possibilities for tuning the structural, electronic, optical, and magnetic properties of perovskites to simultaneously harvest energy using more than one mechanism to realize an improved efficiency. This requires a basic understanding of concepts, mechanisms, corresponding material properties, and the underlying physics involved with these effects.

Mutual Insight on Ferroelectrics and Hybrid Halide Perovskites: A Platform for Future Multifunctional Energy Conversion.

Conjugated polymers and related processing techniques have been developed for organic electronic devices ranging from lightweight photovoltaics to flexible displays. These breakthroughs have recently been used to create organic thermoelectric materials, which have potential for wearable heating and cooling devices, and near-room-temperature energy generation. So far, the best thermoelectric materials have been inorganic compounds (such as Bi2Te3) that have relatively low Earth abundance and are fabricated through highly complex vacuum processing routes. Molecular materials and hybrid organic–inorganic materials now demonstrate figures of merit approaching those of these inorganic materials, while also exhibiting unique transport behaviours that are suggestive of optimization pathways and device geometries that were not previously possible. In this Review, we discuss recent breakthroughs for organic materials with high thermoelectric figures of merit and indicate how these materials may be incorporated into new module designs that take advantage of their mechanical and thermoelectric properties. Thermoelectrics can be used to harvest energy and control temperature. Organic semiconducting materials have thermoelectric performance comparable to many inorganic materials near room temperature. Better understanding of their performance will provide a pathway to new types of conformal thermoelectric modules.

Organic thermoelectric materials for energy harvesting and temperature control

Conducting polymers (CPs) have received much attention in both fundamental and practical studies because they have electrical and electrochemical properties similar to those of both traditional semiconductors and metals. CPs possess excellent characteristics such as mild synthesis and processing conditions, chemical and structural diversity, tunable conductivity, and structural flexibility. Advances in nanotechnology have allowed the fabrication of versatile CP nanomaterials with improved performance for various applications including electronics, optoelectronics, sensors, and energy devices. The aim of this review is to explore the conductivity mechanisms and electrical and electrochemical properties of CPs and to discuss the factors that significantly affect these properties. The size and morphology of the materials are also discussed as key parameters that affect their major properties. Finally, the latest trends in research on electrochemical capacitors and sensors are introduced through an in-depth discussion of the most remarkable studies reported since 2003.

Electrical and Electrochemical Properties of Conducting Polymers.

In this paper, we review recent advances in the development of flexible thermoelectric materials and devices for wearable human body-heat energy harvesting applications. We identify various emerging applications such as specialized medical sensors where wearable thermoelectric generators can have advantages over other energy sources. To meet the performance requirements for these applications, we provide detailed design guidelines regarding the properties of the material, device dimensions, and gap fillers by performing realistic device simulations with important parasitic losses taken into account. For this, we review recently emerging flexible thermoelectric materials suited for wearable applications, such as polymer-based materials and screen-printed paste-type inorganic materials. A few examples among these materials are selected for thermoelectric device simulations in order to find optimal design parameters for wearable applications. Finally we discuss the feasibility of scalable and cost-effective manufacturing of thermoelectric energy harvesting devices with desired dimensions.

Flexible thermoelectric materials and device optimization for wearable energy harvesting

The discovery and development of novel materials in the field of energy are essential to accelerate the transition to a low-carbon economy. Bringing recent technological innovations in automation, robotics and computer science together with current approaches in chemistry, materials synthesis and characterization will act as a catalyst for revolutionizing traditional research and development in both industry and academia. This Perspective provides a vision for an integrated artificial intelligence approach towards autonomous materials discovery, which, in our opinion, will emerge within the next 5 to 10 years. The approach we discuss requires the integration of the following tools, which have already seen substantial development to date: high-throughput virtual screening, automated synthesis planning, automated laboratories and machine learning algorithms. In addition to reducing the time to deployment of new materials by an order of magnitude, this integrated approach is expected to lower the cost associated with the initial discovery. Thus, the price of the final products (for example, solar panels, batteries and electric vehicles) will also decrease. This in turn will enable industries and governments to meet more ambitious targets in terms of reducing greenhouse gas emissions at a faster pace. The discovery and development of advanced materials are imperative for the clean energy sector. We envision that a closed-loop approach, which combines high-throughput computation, artificial intelligence and advanced robotics, will sizeably reduce the time to deployment and the costs associated with materials development.

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Accelerating the discovery of materials for clean energy in the era of smart automation

The development of organic semiconductors for use in thermoelectrics requires the optimization of both their thermopower and electrical conductivity. Here two fundamentally different doping mechanisms are used to investigate the thermoelectric properties of known high hole mobility polymers: poly 3-hexylthiophene (P3HT), poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14), and poly(2,5-bis(thiphen-2-yl)-(3,7-diheptadecantyltetrathienoacene)) (P2TDC17-FT4). The small molecule tetrafluorotetracyanoquinodimethane (F4TCNQ) is known to effectively dope these polymers, and the thermoelectric properties are studied as a function of the ratio of dopant to polymer repeat unit. Higher electrical conductivity and values of the thermoelectric power factor are achieved by doping with vapor-deposited fluoroalkyl trichlorosilanes. The combination of these data reveals a striking relationship between thermopower and conductivity in thiophene-based polymers over a large range of electrical conductivity that is independent of the means of electrical doping. This relationship is not predicted by commonly used transport models for semiconducting polymers and is demonstrated to hold for other semiconducting polymers as well.

Impact of the Doping Method on Conductivity and Thermopower in Semiconducting Polythiophenes

The thermoelectric properties of a highperformance electron-conducting polymer, (P(NDIOD-T2), extrinsically doped with dihydro-1H-benzoimidazol-2-yl (NDBI) derivatives, are reported. The highest thermoelectric power factor that has been reported for a solution-processed n-type polymer is achieved; and it is concluded that engineering polymerdopant miscibility is essential for the development of organic thermoelectrics.

Solubility-Limited Extrinsic n-Type Doping of a High Electron Mobility Polymer for Thermoelectric Applications

The electrical performance of doped semiconducting polymers is strongly governed by processing methods and underlying thin-film microstructure. We report on the influence of different doping methods (solution versus vapor) on the thermoelectric power factor (PF) of PBTTT molecularly p-doped with F n TCNQ (n = 2 or 4). The vapor-doped films have more than two orders of magnitude higher electronic conductivity (σ) relative to solution-doped films. On the basis of resonant soft x-ray scattering, vapor-doped samples are shown to have a large orientational correlation length (OCL) (that is, length scale of aligned backbones) that correlates to a high apparent charge carrier mobility (μ). The Seebeck coefficient (α) is largely independent of OCL. This reveals that, unlike σ, leveraging strategies to improve μ have a smaller impact on α. Our best-performing sample with the largest OCL, vapor-doped PBTTT:F4TCNQ thin film, has a σ of 670 S/cm and an α of 42 μV/K, which translates to a large PF of 120 μW m-1 K-2. In addition, despite the unfavorable offset for charge transfer, doping by F2TCNQ also leads to a large PF of 70 μW m-1 K-2, which reveals the potential utility of weak molecular dopants. Overall, our work introduces important general processing guidelines for the continued development of doped semiconducting polymers for thermoelectrics.

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Morphology controls the thermoelectric power factor of a doped semiconducting polymer

Identifying how small molecular acceptors pack with polymer donors in thin and thick (bulk) films is critical to understanding the nature of electrical doping by charge transfer. In this study, the...

Anne M. Glaudell

Papers

Organic thermoelectric materials for energy harvesting and temperature control

Impact of the Doping Method on Conductivity and Thermopower in Semiconducting Polythiophenes

Solubility-Limited Extrinsic n-Type Doping of a High Electron Mobility Polymer for Thermoelectric Applications

Morphology controls the thermoelectric power factor of a doped semiconducting polymer

Molecular Interactions and Ordering in Electrically Doped Polymers: Blends of PBTTT and F4TCNQ