Dependence of Seebeck Coefficient on the Density of States in Organic Semiconductors

Xiao-Hong, Shi; Sun, Jie

doi:10.1109/led.2017.2765458

Cited by 11 publications

(4 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This approach is more widely applicable than the simpler Mott formula 20 and has the advantage of connecting α to the average entropy per carrier. Since these expressions are valid (neglecting correlation effects) across all doping levels regardless of the conduction mechanism or the semiconductor’s crystalline, semi-crystalline, or amorphous nature, they support numerous mechanisms of conduction in disordered semiconductors 21–23 , including hopping models based on the Miller–Abrahams 24 and Marcus 25 jump rates, that add to our physical explanation of charge transport in conjugated polymers and provide structural design criteria for improving their performance.…”

Section: Introductionmentioning

confidence: 90%

Tuning charge transport dynamics via clustering of doping in organic semiconductor thin films

et al. 2019

View full text Add to dashboard Cite

A significant challenge in the rational design of organic thermoelectric materials is to realize simultaneously high electrical conductivity and high induced-voltage in response to a thermal gradient, which is represented by the Seebeck coefficient. Conventional wisdom posits that the polymer alone dictates thermoelectric efficiency. Herein, we show that doping — in particular, clustering of dopants within conjugated polymer films — has a profound and predictable influence on their thermoelectric properties. We correlate Seebeck coefficient and electrical conductivity of iodine-doped poly(3-hexylthiophene) and poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-3,6-diyl)-alt-(2,2′;5′,2′′;5′′,2′′′-quaterthiophen-5,5′′′-diyl)] films with Kelvin probe force microscopy to highlight the role of the spatial distribution of dopants in determining overall charge transport. We fit the experimental data to a phonon-assisted hopping model and found that the distribution of dopants alters the distribution of the density of states and the Kang–Snyder transport parameter. These results highlight the importance of controlling dopant distribution within conjugated polymer films for thermoelectric and other electronic applications.

show abstract

Section: Introductionmentioning

confidence: 90%

Tuning charge transport dynamics via clustering of doping in organic semiconductor thin films

et al. 2019

View full text Add to dashboard Cite

show abstract

“…To realize a high PF of the OTMs, feasible strategies involving a valid approach to sharpen the local increase of density of states (DOS) nearby the Fermi level ( E F ) of the materials deliver a predictable means to modify their S . − Alternatively, an ion accumulation mechanism with the incorporation of ionic liquid at the surface enables another channel to increase the S of the samples . On the other hand, molecular design with the concept of low effective masses of charge carriers (that is, an intrinsic high mobility) renders an effective way to screen out satisfactory OTMs with high σ. − Besides, side chain engineering by introducing large polarity oxyalkyl chains provides additional technique to facilitate the coprocessing of dopant/polymer pairs, which is beneficial to improving the molecular arrangement for σ-enhancement. , Nevertheless, chemical doping is the essential requirement for OTMs due to the intrinsic low σ, − and therefore endeavors to clarify the differences of doping behaviors of the OTMs on account of the variation of molecular parameters are more significant. − Here, the electrical properties of the doped organic semiconductors are mainly dominated by the thermal activation energy of conductivity ( E act ,σ ) which can be inferred from the Coulomb binding energy ( E coul,ICTC ) or static energy disorder (σ ICTC ) of the integer charge transfer complexes (ICTCs) at low or high doping concentrations, respectively .…”

Section: Introductionmentioning

confidence: 99%

Significantly Reduced Thermal-Activation Energy for Hole Transport via Simple Donor Engineering: Understanding the Role of Molecular Parameters for Thermoelectric Behaviors

Zhong

Yin

Chen

et al. 2020

ACS Appl. Mater. Interfaces

View full text Add to dashboard Cite

Thermal activation energy for charge transfer (E act,σ ) plays a crucial role in determining the electrical properties of organic semiconductors, which are largely dominated by the Coulomb binding energy (E coul,ICTC) or static energy disorder (σICTC) of the formed integer charge transfer complexes at low or high doping concentration, respectively. Herein, we provide two typical donor–acceptor type polymers with distinct donors to disclose the role of molecular parameters in response for their corresponding thermoelectric (TE) behaviors. Noticeably, both the E coul,ICTC and σICTC of the polymers can be effectively restrained by varying the initial carbazole (CZ) donor to the dithieno[3,2-b:2′,3′-d]pyrrole (DTP) moiety, which contributes to the remarkably decreased E act,σ values of the PDTP-DPP than that of PCZ-DPP. Accordingly, the optimized power factors (PF) for PDTP-DPP (10.8 μW m–1 K–2) is almost 5 times higher than the primary PCZ-DPP (1.8 μW m–1 K–2) at ambient condition. In addition, a further improved PF over 85.5 μW m–1 K–2 can be achieved by PDTP-DPP at 488 K due to the synergy of thermal-induced dedoping and thermal-activated semiconducting behavior. Ultraviolet photoelectron and X-ray photoelectron spectroscopy measurements confirm the lower thermal activation energy for efficient p-doping of PDTP-DPP than that of PCZ-DPP.

show abstract

“…This value changed to positive value of 1.14 after doping. In ideal, scattering parameter have values from r = −1/2 for the acoustic phonon scattering to r = 3/2 for ionized impurities scattering 24,25 . There is relatively large deviation for the scattering parameter values of pristine and Joule-annealed CNT yarn in this system.…”

Section: Discussionmentioning

confidence: 99%

Controlling Electronic States of Few-walled Carbon Nanotube Yarn via Joule-annealing and p-type Doping Towards Large Thermoelectric Power Factor

Myint

Nishikawa

Omoto

et al. 2020

Sci Rep

View full text Add to dashboard Cite

Flexible, lightweight and robust thermoelectric (TE) materials have attracted much attention to convert waste heat from low-grade heat sources, such as human body, to electricity. Carbon nanotube (CNT) yarn is one of the potential TE materials owing to its narrow band-gap energy, high charge carrier mobility, and excellent mechanical property, which is conducive for flexible and wearable devices. Herein, we propose a way to improve the power factor of CNT yarns fabricated from few-walled carbon nanotubes (FWCNTs) by two-step method; Joule-annealing in the vacuum followed by doping with ptype dopants, 2,3,5,6-tetrafluo-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Numerical calculations and experimental results explain that Joule-annealing and doping modulate the electronic states (Fermi energy level) of FWCNTs, resulting in extremely large thermoelectric power factor of 2250 µW m −1 K −2 at a measurement temperature of 423 K. Joule-annealing removes amorphous carbon on the surface of the CNT yarn, which facilitates doping in the subsequent step, and leads to higher Seebeck coefficient due to the transformation from (semi) metallic to semiconductor behavior. Doping also significantly increases the electrical conductivity due to the effective charge transfers between CNT yarn and F4TCNQ upon the removal of amorphous carbon after Joule-annealing. Nowadays, personnel electronic devices are ubiquitous in our daily lives. However, these devices heavily rely on batteries for operation while there are various forms of heat (energy) dissipated into our environment including our body heat as a waste 1,2. Therefore, flexible thermoelectric (TE) device becomes a promising technology to power the personal electronic devices from surrounding waste heat. The performance of the TE materials is usually determined by the dimensionless figure of merit, ZT = S 2 σ T/κ, where S is the Seebeck coefficient or thermopower (V K −1), σ is the electrical conductivity (S cm −1), T is the absolute temperature (K) and κ is the thermal conductivity (W m −1 K −1) 3. Power factor, P = S 2 σ can also be used alternatively to explain the thermoelectric performance of materials 4-7. Recently, TE performance has been optimized through formation of nanocomposite with conducting polymers, point defect engineering, energy filtering, controlling the density of state, and so on 8-10. Consequently, many semiconductors that provide the best TE performance are costly to fabricate since they are based on inorganic counterparts. Due to the scarcity of raw materials, and toxicity, inorganic semiconductors have a lot of drawbacks for fabrication of ubiquitous TE generators 11,12. Carbon nanotube (CNT) yarn is one of the potential ubiquitous TE materials because flexible, wearable, lightweight and robust TE devices can be easily fabricated from CNT yarn 9. Moreover, the carrier type of the CNT yarn can be easily altered by simple doping, paving it for using in various wearable or flexible TE applications 1,13,14. Several methods have been attempted to improve the T...

show abstract

Dependence of Seebeck Coefficient on the Density of States in Organic Semiconductors

Cited by 11 publications

References 22 publications

Tuning charge transport dynamics via clustering of doping in organic semiconductor thin films

Tuning charge transport dynamics via clustering of doping in organic semiconductor thin films

Significantly Reduced Thermal-Activation Energy for Hole Transport via Simple Donor Engineering: Understanding the Role of Molecular Parameters for Thermoelectric Behaviors

Controlling Electronic States of Few-walled Carbon Nanotube Yarn via Joule-annealing and p-type Doping Towards Large Thermoelectric Power Factor

Contact Info

Product

Resources

About