• Title/Summary/Keyword: Electron-hole recombination

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THE EFFECT OF DOPANT OUTDIFFUSION ON THE NEUTRAL BASE RECOMBINATION CURRENT IN Si/SiGe/Si HETEROJUNCTION BIPOLAR TRANSISTORS

  • Ryum, Byung-R.;Kim, Sung-Ihl
    • ETRI Journal
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    • v.15 no.3
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    • pp.61-69
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    • 1994
  • A new analytical model for the base current of Si/SiGe/Si heterojunction bipolar transistors(HBTs) has been developed. This model includes the hole injection current from the base to the emitter, and the recombination components in the space charge region(SCR) and the neutral base. Distinctly different from other models, this model includes the following effects on each base current component by using the boundary condition of the excess minority carrier concentration at SCR boundaries: the first is the effect of the parasitic potential barrier which is formed at the Si/SiGe collector-base heterojunction due to the dopant outdiffusion from the SiGe base to the adjacent Si collector, and the second is the Ge composition grading effect. The effectiveness of this model is confirmed by comparing the calculated result with the measured plot of the base current vs. the collector-base bias voltage for the ungraded HBT. The decreasing base current with the increasing the collector-base reverse bias voltage is successfully explained by this model without assuming the short-lifetime region close to the SiGe/Si collector-base junction, where a complete absence of dislocations is confirmed by transmission electron microscopy (TEM)[1].The recombination component in the neutral base region is shown to dominate other components even for HBTs with a thin base, due to the increased carrier storage in the vicinity of the parasitic potential barrier at collector-base heterojunction.

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Research and Development Trend of Carrier Selective Energy Contact Solar Cells (전하선택형 태양전지의 연구개발 동향)

  • Cho, Eun-Chel;Cho, Young Hyun;Yi, Junsin
    • Current Photovoltaic Research
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    • v.6 no.2
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    • pp.43-48
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    • 2018
  • The traditional silicon heterojunction solar cells consist of intrinsic amorphous silicon to prevent recombination of the silicon surface and doped amorphous silicon to transport the photo-generated electrons and holes to the electrode. Back contact solar cells with silicon heterojunction exhibit very high open-circuit voltages, but the complexity of the process due to form the emitter and base at the backside must be addressed. In order to solve this problem, the structure, manufacturing method, and new materials enabling the carrier selective contact (CSC) solar cell capable of achieving high efficiency without using a complicated structure have recently been actively developed. CSC solar cells minimize carrier recombination on metal contacts and effectively transfer charge. The CSC structure allows very low levels of recombination current (eg, Jo < 9fA/cm2), thereby achieves high open-circuit voltage and high efficiency. This paper summarizes the core technology of CSC solar cell, which has been spotlighted as the next generation technology, and is aiming to speed up the research and development in this field.

Thermodynamic Control in Competitive Anchoring of N719 Sensitizer on Nanocrystalline $TiO_2$ for Improving Photoinduced Electrons

  • Lim, Jong-Chul;Kwon, Young-Soo;Song, In-Young;Park, Sung-Hae;Park, Tai-Ho
    • Proceedings of the Korean Vacuum Society Conference
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    • 2011.08a
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    • pp.68-69
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    • 2011
  • The process of charge transfer at the interface between two semiconductors or between a metal and a semiconductor plays an important role in many areas of technology. The optimization of such devices requires a good theoretical description of the interfaces involved. This, in turn, has motivated detailed mechanistic studies of interfacial charge-transfer reactions at metal/organic, organic/organic, and organic/inorganic semiconductor heterojunctions. Charge recombination of photo-induced electron with redox species such as oxidized dyes or triiodide or cationic HTM (hole transporting materials) at the heterogeneous interface of $TiO_2$ is one of main loss factors in liquid junction DSSCs or solid-state DSSCs, respectively. Among the attempts to prevent recombination reactions such as insulating thin layer and lithium ions-doped hole transport materials and introduction of co-adsorbents, although co-adsorbents retard the recombination reactions as hydrophobic energy barriers, little attention has been focused on the anchoring processes. Molecular engineering of heterogeneous interfaces by employing several co-adsorbents with different properties altered the surface properties of $TiO_2$ electrodes, resulting to the improved power conversion efficiency and long-term stability of the DSSCs. In this talk, advantages of the coadsorbent-assisted sensitization of N719 in preparation of DSSCs will be discussed.

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Improvement of Solar Cell Efficiency according to AC Voltage Variation of Electron Relay Enhancer in High Efficient Solar Cell System using Electron Relay Enhancer (전자전달증대기를 이용한 고효율 태양전지 시스템에서 전자전달증대기 입력 교류 전압 변화에 따른 태양전지 효율 향상에 대한 연구)

  • Kim, Hak Soo;Ryu, Young Kee;Lee, Hyuk;Yun, So Young
    • Journal of the Korean Vacuum Society
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    • v.22 no.3
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    • pp.168-173
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    • 2013
  • In this paper, we would like to introduce Electron Relay Enhancer (ERE), a supplementary device, which improves commercial solar cell efficiency minimizing electron-hole recombination of solar cell. The ERE in this study is mainly composed of two capacitors which are connected to AC power source and bridge diode system which controls electron flow direction. Two capacitors repeat collecting electrons from solar cell and pumping the collected electrons to load resistance or inverter through the bridge diode system. While one positively charged capacitor collect electrons, the other negatively charged one pumps electrons. A positively charged capacitor pulls the more exited electrons from the solar cell, before the exited electrons recombine the holes in solar cell. That is why the ERE system enhances solar cell efficiency. As a result, the measured power increase of the solar cell with the ERE is varied from 5.9 W to 25.6 W in each experimental condition. Maximal increase rate of the solar cell power with ERE is 30.8% of solar cell power without ERE.

Local surface potential and current-voltage behaviors of $Cu(In,Ga)Se_2$ thin-films with different Ga/(In+Ga) content (Ga/(In+Ga) 함량비에 따른 $Cu(In,Ga)Se_2$ 박막의 국소적 영역에서의 표면 퍼텐셜과 전류-전압 특성 연구)

  • Kim, G.Y.;Jeong, A.R.;Jo, W.;Jo, H.J.;Kim, D.H.;Sung, S.J.;Hwang, D.K.;Kang, J.K.;Lee, D.H.
    • 한국태양에너지학회:학술대회논문집
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    • 2012.03a
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    • pp.149-152
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    • 2012
  • $Cu(In,Ga)Se_2$ (CIGS) is one of the most promising photovoltaic materials because of large conversion efficiency which has been achieved with an optimum Ga/(In+Ga) composition in $CuIn_{1-x}Ga_xSe_2$ (X~0.3). The Ga/(In+Ga) content is important to determine band gap, solar cell performances and carrier behaviors at grain boundary (GB). Effects of Ga/(In+Ga) content on physical properties of the CIGS layers have been extensively studied. In previous research, it is reported that GB is not recombination center of CIGS thin-film solar cells. However, GB recombination and electron-hole pair behavior studies are still lacking, especially influence of with different X on CIGS thin-films. We obtained the GB surface potential, local current and I-V characteristic of different X (00.7 while X~0.3 showed higher potential than 100 mV on GBs. Higher potential on GBs appears positive band bending. It can decrease recombination loss because of carrier separation. Therefore, we suggest recombination and electron-hole behaviors at GBs depending on composition of X.

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Interlayer Engineering with Different Host Material Properties in Blue Phosphorescent Organic Light-Emitting Diodes

  • Lee, Jong-Hee;Lee, Jeong-Ik;Lee, Joo-Won;Chu, Hye-Yong
    • ETRI Journal
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    • v.33 no.1
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    • pp.32-38
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    • 2011
  • We investigated the light-emitting performances of blue phosphorescent organic light-emitting diodes, known as PHOLEDs, by incorporating an N,N'-dicarbazolyl-3,5-benzen interlayer between the hole transporting layer and emitting layer (EML). We found that the effects of the introduced interlayer for triplet exciton confinement and hole/electron balance in the EML were exceptionally dependent on the host materials: 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole, 9-(4-tert-butylphenyl)-3,6-ditrityl-9H-carbazole, and 4,4'-bis-triphenylsilanyl-biphenyl. When an appropriate interlayer and host material were combined, the peak external quantum efficiency was greatly enhanced by over 21 times from 0.79% to 17.1%. Studies on the recombination zone using a series of host materials were also conducted.

The Carrier Diffusion Modeling of CSP-DH Semiconductor Laser Structures (CSP-DH 구조 반도체 레이저의 캐리어 확산 방정식을 위한 모델링)

  • Lee, S.T.;Jeon, H.S.;Lee, C.Y.;Um, K.Y.;Yoon, J.W.;Yoon, S.B.;Oh, H.S.
    • Proceedings of the KIEE Conference
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    • 1988.07a
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    • pp.469-471
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    • 1988
  • The basic modeling is analyzed on the optoelectronic properties of CSP-DH laser structure using self-consistent calculation of optical field and the electron-hole distribution in the active region. Laser properties is modelled include gain profile, threshold, near field and far field pattern. This new characterization is allowed for consideration such as carrier spatial hole burning due to strong optical fields which stimulate recombination.

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Cathodoluminescence Enhancement of CaTiO3:Pr3+ by Ga Addition

  • Kang, Seung-Youl;Byun, Jung-Woo;Kim, Jin-Young;Suh, Kyung-Soo;Kang, Seong-Gu
    • Bulletin of the Korean Chemical Society
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    • v.24 no.5
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    • pp.566-568
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    • 2003
  • The phosphor $CaTiO_3:Pr^{3+}$ attracts much attention as a low-voltage red phosphor because of its good chromaticity and intrinsic conductivity. The addition of Ga into this CaTiO₃:Pr led the luminance intensity to greatly enhance without the change of the wavelength for the electronic transition and the peak shape of it. The increase of the recombination rate of electron-hole pairs through the Ga ion doping, which was expected to play a role of a hole-trap center, is proposed to be one of the reasons for the enhancement of the cathodoluminescence intensity.

Relaxation of Photogenerated Carriers under He, $H_2, Co_2 and\; O_2$ on ZnO

  • 한종수;김혜정;진준
    • Bulletin of the Korean Chemical Society
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    • v.19 no.6
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    • pp.676-680
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    • 1998
  • The relaxation process of photogenerated carriers was investigated using conductivity measurement on ZnO under He, $H_2,\; CO_2\; and\; O_2$. The process was well explained with the rate constant of reaction or recombination of hole and electron, $k_h \;and\; k_e ( k_h > k_e)$, respectively. Generally, $k_h$ increased with the pressure of the gases. The slope of $k_h$ with respect to the pressure increased in the order of $H_2{\le}He, while $k_h$ of $O_2$ was sensitive to the history of the sample. The relaxation process on ZnO which was exposed to oxygen at 298 K and 573 K was observed during the illumination at 298 K and it was found that the rate constant of hole decreased with illumination time. From the result, it was suggested that the rate constant of photogenerated excess carriers was affected by the surface barrier of the semiconductor.

The Characteristices of the 4,4',4'-trifluoro-triazine as a hole Blocking Material in Electroluminescent Devices (전계발광 소자에서 정공 차단 물질로서의 4,4',4'-trifluoro-triazine의 특성)

  • Shin, Ji-Won;Shin, Dong-Muyng;Sohn, Byoung-Chung
    • Journal of the Korean Applied Science and Technology
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    • v.17 no.2
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    • pp.120-125
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    • 2000
  • The tfTZ(4,4',4''-trifluoro-triazine) was used as a hole blocking material for the electroluminescent devices(ELDs) in this study. In general, the holes are outnumbered the electrons in hole transport and emitting layers because the hole transport is more efficient in most organic ELDs. The hole blocking layer are expected to control the excess holes to increase the recombination of holes and electrons and to decrease current density. The former study using the 2,4,6-triphenyl-1,3,5-triazine(TTA) as hole blocking layer showed that the TTA did not form stable films with vapor deposition technique. The tfTZ can generate stable evaporated films, moreover the fluorine group can lower the highest occupied molecular orbital(HOMO) level, which produces the energy barrier for the holes. The tfTZ has high electron affinities according to the data by the Cyclic-Voltammety(CV) method, which is developed for the measurement of HOMO and lowest occupied molecular orbital(LUMO) level of organic thin films. The lowered HOMO level is made the tfTZ to be applied for a hole blocking layer in ELDs. We fabricated multilayer ELDs with a structure of ITO/hole blocking layer(HBL)/hole transporting layer(HTL)/emitting layer/electrode. The hole blocking properties of this devices is confirmed from the lowered current density values compared with that without hole blocking layer.