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|Title:||Bismuth telluride / PEDOT:PSS composites for flexible thermoelectric generators||Authors:||Lin, Shuping||Degree:||Ph.D.||Issue Date:||2021||Abstract:||Thermoelectric (TE) generators are regards as environmentally friendly technology for harvesting and recovering heat and converting it into electrical energy. Light and flexible thermoelectric generators are much desirable for numerous applications of wearable microelectronics, internet of things, and waste heat recovery. However, their progress has been hindered by the shortage of such thermoelectric materials. The various designed flexible thermoelectric generators (FTEGs) using these materials are also limited. Thus, the systematic study of both p-and n-type TE materials in one system and the affected device performance remains muted. To address the problems, in this thesis, functional Bi0.52 Sb1.48Te3/ PEDOT:PSS and Bi2Te2.68Se0.32/PEDOT:PSS flexible thermoelectric composites have been explored in the room temperature range, aiming at producing various structure FTEGs. Annealing effects on the behavior of Bi0.52 Sb1.48Te3/PEDOT:PSS and Bi2Te2.68Se0.32/PEDOT:PSS, are discussed and compared. The satup gradient annealing temperature (423K, 593K, 623K, 673K) is programmed on the basis of the stability and configuration state of the PEDOT:PSS, observing the annealing effect on the performance of configuration state of Bi0.52Sb1.48Te3/PEDOT:PSS, Bi2Te2.68Se0.32/PEDOT:PSS composites. The resultant composites exhibit a surprising synergy that the composite Seebeck coefficients are higher than those of the constituent alloys and conductive polymer. The Seebeck coefficient of the optimized TE compsites exhibit superior Seebeck coefficient, power factor and figure of merit among BixTey/PEDOT:PSS composites reported so far. The Bi0.52 Sb1.48Te3/ and Bi2Te2.68Se0.32/PEDOT:PSS thermoelectric composites advanced room-temperature performance explored in this work are suitable for flexible printed film-structure and sandwich-like strcuture thermoelectric generators. Furthermore, thin-film and sandwich structured flexible thermoelectric generators have been developed in a systematic investigation in terms of device structure and fabrication processes. For Bi0.52Sb1.48Te3/PEDOT:PSS thermoelectric composite, The Seebeck coefficient of the optimized Bi0.52Sb1.48Te3/PEDOT:PSS sample is 273.3 μV/K at room temperature, reaching that of pure Bi0.52Sb1.48Te3, representing the highest value for BixTey/PEDOT:PSS composites reported so far. The measured thermal conductivity of the resultant composites is within the range from 0.28 to 0.46 W/(m·K) with the enhanced thermal treatments, and their Seebeck coefficient from 168.9 to 273.3 μV/K with power factors from 4.12 to 473.5 μW/(m·K2) near room temperature, respectively. The corresponding power factor and ZT are 473.5 μW/m·K2 and 0.4, respectively. The possible influential factors related to the TE performace are disscussed. For the Bi2Te2.68Se0.32 /PEDOT:PSS composites, the Seebeck coefficient of the optimized Bi2Te2.68Se0.32 /PEDOT:PSS sample is -218.0 μV/K at room temperature, reaching that of pure n-Bi2Te3, representing the highest value for BixTey/PEDOT:PSS composites reported so far. The corresponding power factor and ZT are 306μW/m·K2 and 0.23, respectively. The measured thermal conductivity of the resultant composites is within the range from 0.32 to 0.54 Wm-1K-1, and their Seebeck coefficient from -166.3 to -218.0 μV/K with power factors from 8.79 to 305.79 μW/(m·K2) near room temperature, respectively. The behavior of the Bi2Te2.68Se0.32 /PEDOT:PSS is different from the p-type ones and the corresponding poosible resaons are proposed.
Furthermore, two types, film structure and sandwich-like strcture FTEGs are desinged and fabricated using these versatile p-/n-type materials. These two protypes are based on the different varying degrees of thermal treatments of the TE mateirals. Moderate annealing treatment is applicable to fabricate film type FTEGs. The paper-based FTEG possesses a high output power, specific and areal power density as well as excellent flexibility. FTEGs were fabricated by disperse printing on aramid paper and PDMS substrate, respectively. With ΔT = 70 K, the paper-based thermoelectric generator demonstrates a high output power of 30.8 μW, specific power density of 12.3 μW/g and areal power density of 20.5 μW/cm2. High flexibility and durability have been displayed in cyclic bending tests of PDMS-based thermoelectric generators. The variation in electric resistance is negligible even after 100,000 bending cycles up to 2.5 cm-1 curvature. The solution-processible, soft and flexible composites offer unique advantages that are not available to their rigid counterparts. A printed FTEG on polyimide paper circuit board yields a specific output power of 2.5 μW/g, and an areal power density up to 4.0 μW/cm2 when ΔT = 67 K. High-temperature treatment is applicable to fabricate sandwich structure FTEGs. The sandwich-like FTEG possesses the higher output power, specific and areal power density than that of film type FTEGs. For the FTEG with copper fabric, the overall performance demonstrate higher than the one without copper fabric. A sandwich-structured flexible generator equipped with heat sink fabric produces an output power of 9.0 mW with a temperature difference of 45 K, which demonstrates its great promises in wearable microelectronics applications that require a driving power of several mWs. The correspoinding specific output power areal power density are 2.3 mW/g and 0.65 mW/cm2, respectively. The vast difference of almost three orders of magnitude between the two types of FTEGs is attributed to effects of annealing and densification processes, TE leg cross-sectional area, contact resistance, heat sink. In addition, by comparing its performance with the predicted theoretical output power, this work illustrates the large feasible scope for further improvement, and charts up a roadmap of approaches towards achieving the theoretical output upper limit.
Hong Kong Polytechnic University -- Dissertations
|Pages:||xxi, 160 pages : color illustrations|
|Appears in Collections:||Thesis|
View full-text via https://theses.lib.polyu.edu.hk/handle/200/11314
Citations as of May 22, 2022
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