대기중 안정한 MAPbI3에서의 Photo Seebeck 효과

김유성,박병남 대한금속·재료학회 2023 대한금속·재료학회지 Vol.61 No.2

With increasing interest in energy harvesting using heat as a next-generation eco-friendly energysource, organic-inorganic perovskite materials have emerged as promising materials for thermoelectricdevices. In particular, the photo-Seebeck effect of halide perovskite materials has attracted attention due totheir wide optical absorption spectrum and large diffusion length, depending on their composition. MAPbI3,a representative organic perovskite component, has been reported to have a Seebeck coefficient of onlyhundreds of μV/K. In this manuscript, we report a photo-Seebeck effect for bulk MAPbI3 perovskite in whichthe magnitude of the Seebeck coefficient significantly increased by 700 μV/K under illumination with a greenlaser diode. An air-stable perovskite pellet was synthesized using the alcohol substitution synthesis method,and both the Seebeck coefficient and the photocurrent increased in air, proving that enhanced Seebeckcoefficient is associated with the formation of excitons in MAPbI3. X-ray diffraction analysis found that theremnant PbI2 led to n-type electronic transport characterized by a negative Seebeck coefficient. Photo-inducedelectron transfer from MAPbI3 to the PbI2-rich phase under illumination led to dedoping of electrons, to forman MAPbI3 pellet. The significant enhancement in the Seebeck coefficient was found to depend on thecomposition of the remnant PbI2, which alters the majority carrier type in the bulk MAPbI3.

Enhanced Seebeck coefficient by energy filtering in Bi-Sb-Te based composites with dispersed Y₂O₃ nanoparticles

Madavali, Babu,Kim, Hyo-Seob,Lee, Kap-Ho,Hong, Soon-Jik Elsevier 2017 Intermetallics Vol.82 No.-

<P><B>Abstract</B></P> <P>The incorporation of ceramic nanoparticles in the bulk thermoelectric matrix is one of the new strategies to boost the Seebeck coefficient. In this research, different weight percentages of Y<SUB>2</SUB>O<SUB>3</SUB> (2, 4, and 6) nanoparticles (NPs) were incorporated into the pre-alloyed BiSbTe powder for making nanocomposites (NCs) by mechanical milling. The resultant NCs powders were subsequently consolidation by spark plasma sintering (SPS) at 450 °C. The existence of Y<SUB>2</SUB>O<SUB>3</SUB> nano-inclusions was confirmed by x-ray diffraction and TEM-SAED analysis. The hardness of the nanocomposites was significantly improved (>49%) compared to that of pure BiSbTe, and this was attributed to grain-boundary hardening and to a dispersion strengthening mechanism. The electrical conductivity decreased while the Seebeck coefficient significantly improved (45%) at room temperature for the NCs to which 2 wt% Y<SUB>2</SUB>O<SUB>3</SUB> was added. This was due to the scattering of carriers through the energy filtering effect. The electronic component of the thermal conductivity greatly contributed to the reduction of total thermal conductivity (22%) in BiSbTe NCs to which 6 wt% Y<SUB>2</SUB>O<SUB>3</SUB> was added. A peak ZT of 1.24 was achieved for BiSbTe/(2 wt%) Y<SUB>2</SUB>O<SUB>3</SUB> NCs due to reduction in their thermal conductivity and improved Seebeck coefficient values.</P> <P><B>Highlights</B></P> <P> <UL> <LI> P-type BiSbTe/Y<SUB>2</SUB>O<SUB>3</SUB> nanocomposites have been fabricated by ball milling and Spark plasma sintering. </LI> <LI> Seebeck coefficient is eminently improved (45%) due to scattering of carriers through the energy filtering effect. </LI> <LI> Thermal conductivity is reduced by 22% in nanocomposites due to carrier/phonon scattering. </LI> <LI> Hardness of nanocomposites was significantly improved (>49%) compared to pure BiSbTe. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Significant improvement in Seebeck coefficient via energy filtering effect, and strong reduction in thermal conductivity from carrier/phonon scattering contributed to the enhanced ZT at room temperature.</P> <P>[DISPLAY OMISSION]</P>

Effects of Microstructure on Thermoelectric Properties of $FeSi_2$

Park, Joon-Young,Song, Tae-Ho,Lee, Hong-Lim,Pai, Chul-Hoon The Korean Ceramic Society 1996 The Korean journal of ceramics Vol.2 No.1

The variation of electrical conductively and Seebeck coefficient of FeSi2 according to the density of the specimen has been observed over the temperature range 50 to $700^{\circ}C$. A conventional pressureless sintering method with various sintering time (0, 0.5, 1, 5h) at $1190^{\circ}C$ and/or various sintering temperatures(1160, 1175, 1190, $1200^{\circ}C$) for 2 h was carried out to prepare $FeSi_2$ specimens having various densities. The relationship between the electrical conductivity and Seebeck coefficient was investigated after two steps of annealing (at $865^{\circ}C$ and then $800^{\circ}C$ for total 160h) and thermoelectric measurement. The electrical conductivity for the specimens showed a typical tendency of semiconductor, the average activation energy of which in the intrinsic region (above $300^{\circ}C$) was observed approximately as 0.452 eV, and increased slightly with density. On the other hand, the specimen of the lower density showed the higher value of Seebeck coefficient in the intrinsic region. As the temperature fell into the non-degenerate region, the highly densified specimen which had relatively little residual metal phase showed the higher value of Seeback coefficient. The power factor of all specimens showed the optimum value at $200^{\circ}C$. However, the power factor of the specimen of the lower density increased again from $400^{\circ}C$ and that of the higher dense specimen increased from $500^{\circ}C$. The power factor was more affected by Seebeck coefficient than electrical conductivity over all temperature range.

Conductivity, carrier density, mobility, Seebeck coefficient, and power factor in V₂O₅

Kang, M.,Jung, J.,Lee, S.Y.,Ryu, J.W.,Kim, S.W. Elsevier 2014 Thermochimica acta Vol.576 No.-

The thermophysical properties of V<SUB>2</SUB>O<SUB>5</SUB> films as functions of temperature and crystallization are investigated and characterized by measuring the Hall and Seebeck coefficients. The carrier density and electrical conductivity of the amorphous and crystalline V<SUB>2</SUB>O<SUB>5</SUB> films increase with increasing temperature and show a strong dependence on the crystallization. However, the carrier mobility of the films is inversely proportional to temperature and crystallization due to increased carrier scattering in terms of the thermal phonon and boundaries by the crystallites. The Seebeck coefficients of the films are negative, indicating n-type conduction, and show a stronger dependence on crystallization than temperature. In particular, the crystalline V<SUB>2</SUB>O<SUB>5</SUB> film demonstrates considerably large Seebeck coefficients in the range of -385 to -436μVK<SUP>-1</SUP> from 300 to 410K. Both power factors of the films are calculated to be 5.76x10<SUP>-9</SUP> and 3.12x10<SUP>-7</SUP>Wm<SUP>-1</SUP>K<SUP>-2</SUP> at 410K, respectively.

Co 첨가 Fe-Si n형 반도체의 전기적 특성

배철훈 ( Chul Hoon Pai ),김정곤 ( Jeung Gon Kim ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.12

The effect of Co additive on the electrical properties of Fe-Si alloys prepared by a RF inductive furnace was investigated. The electrical conductivity and Seebeck coefficient were measured as a function of the temperature under an Ar atmosphere to evaluate their applicability to thermoelectric energy conversion. The electrical conductivity of the specimens increased as the temperature increased, showing typical semiconducting behavior. The electrical conductivity of Co-doped specimens was higher than that of undoped specimens and increased slightly as the amount of Co additive increased. This is most likely due to the difference in the carrier concentration and the amount of residual metallic phase ε-FeSi (The ε-FeSi was detected in spite of an annealing treatment of 100 h at 830℃). Additionally, metallic conduction increased slightly as the amount of Co additive increased. On the other hand, Co-doped specimens showed a lower Seebeck coefficient due to the metallic phase. The power factor of Co-doped specimens was higher than that of undoped specimens. This would be affected more by the electrical conductivity compared to the Seebeck coefficient.

N형 SiC 반도체의 열전 물성에 미치는 적층 결함의 영향

배철훈(Chul-Hoon Pai) 한국산학기술학회 2021 한국산학기술학회논문지 Vol.22 No.3

n형 SiC 반도체에서 적층 결함이 열전 물성에 미치는 영향에 대해 연구하였다. β-SiC 분말 성형체를 질소 분위기에서 1600∼2100 ℃, 20∼120분간 열처리해서 30∼42 %의 기공률을 갖는 다공질 SiC 반도체를 제작하였다. X선회절 분석으로 적층 결함량, 격자 스트레인 및 격자 상수를 산출하였고, 미세 구조 분석을 위해서 기공률 및 비표면적 측정과 함께, 주사 전자현미경 (SEM), 투과 전자현미경 (TEM) 및 고분해능 전자현미경 (HREM) 등을 관찰하였다. Ar 분위기 550∼900 ℃에서 도전율과 Seebeck 계수를 측정 및 산출하였다. 열처리 온도가 높을수록, 처리 시간이 길어질수록 캐리어 농도 증가 및 입자와 입자간의 연결성 향상에 의해 도전율이 향상되었다. 도너로 작용하는 질소의 고용으로 Seebeck 계수는 음(-)의 값을 나타내었고, 도전율과 마찬가지로 열처리 온도 및 시간이 상승함에 따라 Seebeck 계수의 절대 값이 증가하였다. 이는 적층 결함의 감소, 즉 입자 및 결정 성장과 함께 적층 결함 밀도의 감소에 의해 포논의 평균자유 행정이 증가해서 결과적으로 포논-드랙 효과에 의한 Seebeck 계수의 향상으로 나타난 것으로 판단된다. This study examined the effects of stacking faults on the thermoelectric properties for n-type SiC semiconductors. Porous SiC semiconductors with 30∼42 % porosity were fabricated by the heat treatment of pressed β-SiC powder compacts at 1600∼2100 ℃ for 20∼120 min in an N2 atmosphere. XRD was performed to examine the stacking faults, lattice strain, and precise lattice parameters of the specimens. The porosity and surface area were analyzed, and SEM, TEM, and HRTEM were carried out to examine the microstructure. The electrical conductivity and the Seebeck coefficient were measured at 550∼900 °C in an Ar atmosphere. The electrical conductivity increased with increasing heat treatment temperature and time, which might be due to an increase in carrier concentration and improvement in grain-to-grain connectivity. The Seebeck coefficients were negative due to nitrogen behaving as a donor, and their absolute values also increased with increasing heat treatment temperature and time. This might be due to a decrease in stacking fault density, i.e., a decrease in stacking fault density accompanied by grain growth and crystallite growth must have increased the phonon mean free path, enhancing the phonon-drag effect, leading to a larger Seebeck coefficient.

P형 FeSi₂의 열전물성에 미치는 입자크기 및 첨가물 영향

배철훈(Pai, Chul-Hoon) 한국산학기술학회 2013 한국산학기술학회논문지 Vol.14 No.4

Fe-Si계 합금은 우주탐사용으로 응용되고 있는 Si-Ge합금보다는 낮은 성능지수를 나타내지만 원료가 풍부하여 저가이고, 제조가 간단하며, 800℃까지 사용가능한 중고온용 열전발전재료이다. 본 연구에서는 고주파 진공유도로를 이용 해서 제조한 p형 FeSi₂의 열전물성에 미치는 입자크기 및 첨가물 영향에 대해 조사하였다. 조성입자크기가 작을수록 소결 밀도 증가와 함께 입자와 입자간의 연결성 향상에 의해 도전율이 증가하였다. Seebeck 계수는 600∼800K에서 최고값을 나타내었고, 잔존하는 ε-FeSi 금속전도상에 의해 약간 감소하였다. Fe2O₃ 및 Fe3O₄를 첨가한 경우, 잔존 금속전도상 및 Si 결핍양 증가에 의해 도전율은 증가하였고 Seebeck 계수는 감소하였다. 반면에 SiO₂를 첨가한 경우에는 도전율과 Seebeck 계수 모두 상승하였다. Although Fe-Si based alloy has lower figure of merit than Si-Ge alloy applied for space probe, its low cost related to abundant raw material, rather simple processing, high temperature resistance and reliability up to 800℃ made it one of the most promising middle temperature thermoelectric generation materials. The effect of particle size and additive on the thermoelectric properties of p-FeSi₂ prepared by a RF inductive furnace was investigated. The electrical conductivity increased slightly with decreasing particle size and hence better grain-to-grain connectivity due to the increase of density. The Seebeck coefficient exhibited the maximum value at about 600∼800K and decreased slightly with increasing particle size. This must be due to the amount of residual metallic phase ε-FeSi. Fe2O₃ and/or Fe3O₄-doped specimens showed the higher electrical conductivity and the lower Seebeck coefficient due to increase of the metallic phase and Si-vacancy. On the other hand, SiO₂-doped specimen showed the higher electrical conductivity and the higher Seebeck coefficients.

Thermoelectric Properties of the Kondo Semiconductor CeRu4As12 Prepared under High Pressure

Chihiro Sekine,Tomokazu Kawata,Yukihiro Kawamura,Takehiko Yagi 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.63 No.3

The thermoelectric properties of the Kondo semiconductor CeRu4As12 with a filled skutteruditetypestructure have been studied. The compound CeRu4As12 exhibits a hybridization gap insulatingstate with a small activation energy of 50 K. We report further results for CeRu4As12 synthesized athigh temperatures and high pressures. Seebeck-coefficient and thermal-conductivity measurementshave been performed on this material. The temperature dependence of the Seebeck coefficient forCeRu4As12 shows two peaks (around 90 K and 280 K). The phenomena could be related to theKondo behavior at high temperatures and a hybridization gap-formation process at low temperatures.

벌크 다결정 SnS / PEDOT:PSS 박막 이중층에서의 변조 도핑을 통한 열전 역률 강화

이동욱 대한금속·재료학회 2022 대한금속·재료학회지 Vol.60 No.7

Modulation doping occurs in a heterojunction where a charge carrier-rich material transfers charge to a carrier-deficient material. The modulation-doped material is intentionally selected to have higher charge carrier mobility than the modulation dopant material, so that the overall electrical conductivity can be boosted. Although this modulation doping strategy has proven effective in enhancing power factor in thermoelectrics, selection criteria for such semiconductor couples have not been explicitly clarified, resulting in only a few discovered semiconductor couples available for modulation doping-driven thermoelectric systems [1-4]. Here, we (i) report an electronic band structure-based guideline to actualize modulation doping, (ii) reveal that hole-rich PEDOT:PSS can modulation dope otherwise undoped tin monosulfide (SnS) in their bilayered structure, (iii) prove that modulation doping is responsible for thermoelectric power factor enhancement by comparing computational and experimental Seebeck coefficient and electrical conductivity values. The optimized PEDOT:PSS thin film / SnS pellet bilayered structure had a 134.7 fold improvement in electrical conductivity and a 93.6 fold power factor enhancement over those of undoped SnS, with only a ~ 20 % decrease in Seebeck coefficient. The modulation doping effect can result in further power factor improvement when SnS becomes a nanoscale thin film or nanoparticles in the future.

Effect of multiwalled carbon nanotubes on the thermoelectric properties of a bismuth telluride matrix

Bark, H.,Kim, J.S.,Kim, H.,Yim, J.H.,Lee, H. Elsevier 2013 Current Applied Physics Vol.13 No.suppl2

Carbon nanotubes (CNTs) have been not attractive for thermal energy conversion applications because of their high thermal conductivities and low Seebeck coefficient. In other words, traditional thermoelectric materials are basically low bandgap semiconductors such as bismuth telluride and antimony telluride, which have shown outstanding performance. In this report, we studied the effect of a network consisting of CNTs as an impurity in a matrix of bismuth telluride (Bi<SUB>2</SUB>Te<SUB>3</SUB>) particles. We dispersed Bi<SUB>2</SUB>Te<SUB>3</SUB> particles and CNTs together in a solvent and fabricated composite samples under vacuum filtration. Seven different CNTs concentration, 0, 10, 20, 50, 70, 90, 100 vol% were used to compare the influence of CNTs on electrical conductivity and thermopower of the composites. At the low contents (10 and 20 vol%) of CNTs, the electrical conductivity and the thermopower were a little increased, which can be attributed to p-typed doping effect of CNTs on Bi<SUB>2</SUB>Te<SUB>3</SUB> particles. At the high contents (50, 70 and 90 vol%) of CNTs, the electrical conductivity and the thermopower were decreased, which can be attributed to hindered carrier mobility.