Polymer-based thermoelectric materials:A review of power factor improving strategies

Thermoelectric(TE)materials are receiving increasing attention due to their ability to directly converting heat to electricity.They are used to harvest electrical energy from the wasted heat in order to increase the efficiency of global energy.Polymer-based TE materials are particularly fascinating to wearable and mobile devices due to their low density,good flexibility,and low toxicity.This review summarizes the recent breakthroughs and optimization strategies of polymer-based TE materials.Among a large number of different organic TE materials,those with remarkable TE performance are selected and divided into three categories,which are poly(3,4-ethylenedioxythiophene)derivatives,carbon nanotube/conductive polymer composites,and inorganic semiconductive nanomaterial/polymer composites.The effect of components and structures on the power factor are presented and discussed.Finally,some challenges are described and suggestions are provided for preparing the next-generation of polymer-based materials with high TE performance.

A review of flexible halide perovskite solar cells towards scalable manufacturing and environmental sustainability

The perovskite material has many superb qualities which allow for its remarkable success as solar cells;flexibility is an emerging field for this technology.To encourage commercialization of flexible perovskite solar cells,two main areas are of focus:mitigation of stability issues and adaptation of production to flexible substrates.An in-depth report on stability concerns and solutions follows with a focus on Ruddlesden-Popper perovskites.Roll to roll processing of devices is desired to further reduce costs,so a review of flexible devices and their production methods follows as well.The final focus is on the sustainability of perovskite solar cell devices where recycling methods and holistic environmental impacts of devices are done.

Through-Thickness Thermal Conductivity Prediction Study on Nanocomposites and Multiscale Composites

In this research, a modeling and experimental study was conducted to explore the effects of nanoparticle type (aluminum nanoparticles and carbon nanotubes), filler concentration and interactions between the nanoparticle and reinforcing fibers on through-thickness conductivity of nanoparticle/epoxy nanocomposites and nanoparticle/fiber-reinforced multiscale composites. Multiple, notable micromechanical models were evaluated to predict through-thickness thermal conductivity of both composite systems, and then compared to the experimental results. The results showed that filler volume fraction ranges and thermal conductivity differences of the constituent materials for the thermal conductivity ratio (km/kf or kf/km) used in the models can affect the resulting predictions. Certain models were found to be suitable for varying conditions on the thermal conductivity ratio. Finite element models (FEM) were developed to reveal heat transport mechanisms of the resultant nanocomposites and multiscale composites. The nanocomposite design for finite element analysis (FEA) provided close predictions and performed better than the micromechanical models. On the multiscale composite system, predictions were concluded to be dependent upon the FEM design where the interactions between nanoparticles and fibers are critical to accurately determine the through-thickness thermal conductivity.

Laser Stimulated Shape Memory Polymer with Inclusion of Gold Nanorod—Effect of Aspect Ratio and Critical Role of On-resonance Irradiation

Gold nanorods（AuNRs） are excellent photothermal agents to enable a variety of laser stimulated functional polymers. One key issue is to maximize the photothermal conversion efficiency of Au NRs. In this study, the light responsive AuNR/shape memory polymer（SMP） nanocomposites with inclusion of AuNRs of varied aspect ratios were prepared, characterized, and their laser irradiation induced bending behavior was investigated. The critical role of the on-resonance irradiation condition—a close match of the longitudinal plasmon resonance of the AuNR with the wavelength of the incident laser—has been established.It allows for maximizing the photothermal conversion efficiency of AuNRs to result in the rapid and large deformation of the AuNR/SMP nanocomposites. For the Au NR/SMP nanocomposite films prepared under similar processing conditions, the close-to-resonance irradiation at a 1.27 W/cm^2 was able to induce a bending rate of 27？/s and maximum bending angle of 90.4？. In contrast, the off-resonance irradiation at a 1.89 W/cm^2 resulted in negligible response.

The enhanced power factor of multi-walled carbon nanotube/R stabilized polyacrylonitrile composites due to the partially conjugated structure

The studies of organic thermoelectric(TE)materials mainly focus on conductive polymers due to their conjugated molecular structures and high intrinsic electrical conductivity.When the conductive polymer is mixed with certain insulating polymers,the power factor was found enhanced.It is doubtful that the partially conjugated molecular structure is beneficial to the TE performance.Polyacrylonitrile(PAN)is an insulating polymer with a non-conjugated structure in its backbone,however,it has a partially conjugated structure after thermal treatment.In this work,a composite of PAN and multi-walled carbon nanotubes(MWCNT)was made and thermally treated in order to study the partially conjugated structure on the improvement of the power factor.By controlling the PAN content and the temperature of thermal treatments,a maximum power factor of 22 mW/mK2 was obtained from the MWCNT/PAN composite with 45%PAN content after thermally treated at 300℃in air,which is 300%and 80%higher than that without PAN and before thermal treatment,respectively.It is demonstrated that the partially conjugated polymers play an important role in TE performance and they are promising candidates for high-efficient organic TE materials.