Physical and Electrical Properties of Carbon Nanotubes and Their Application to Photovoltaic Device

Abstract

Carbon nanotubes (CNTs) have excellent electrical and chemical properties, so CNTs have been experimentally researched by many groups for application at various field such as sensor, solar cell and display. Encapsulation of organic/inorganic molecules inside CNTs can be adjusted energy level and advantage high electric field. The hybrid composite single-walled carbon nanotubes (SWNTs) have advantage of organic and inorganic material, it will be next generation material including graphene. In this thesis, hybrid composite SWNTs by encapsulation was made and their properties. In addition, SWNTs were incorporated various type of solar to electrical energy conversion devices (solar cell).

Chapter I introduces a brief history, properties of CNTs, application and purpose of the thesis

Chapter II reports application solar cell incorporating SWNTs or reduced graphene oxide (rGO). First, quantum dot-sensitized solar cells (QDSSCs) research incorporating with SWNTs were studied. QDSSCs were synthesized using CdS and CdSe quantum dots (QDs) incorporated onto one-dimensional ZnO nanorods by successive ionic layer adsorption. In order to get the highest performance of the synthesized cell, the concentration of precursor QDs solution and the number of deposition cycles in the QDs solution were varied together. The photovoltaic performance of each cell was compared with the ultraviolet/visible absorption spectra and incident photon to current efficiency graphs. QDSSCs incorporating SWNTs, sprayed onto the substrate before deposition of the next layer, exhibited enhanced or decreased photocell efficiency compared to that of the pristine cell. In particular, a maximum rate increase of 17% was obtained with the solar cell containing SWNTs in CdSe QDs. Second, hybrid-QDSSCs (h-QDSSCs) research incorporating with SWNTs were studied. Regioregular poly(3-hexylthiophene) (P3HT) is used as a material to substitute for the liquid electrolyte in the QDSSCs. In order to gain high performance of the cell, three different cells using P3HT, pristine P3HT, SWNT-mixed P3HT (mixing), and SWNT-blended P3HT (blended) are made and their photovoltaic cells measure J–V curve, incident photon to current efficiency, and electrochemical impedance spectroscopy. Those values obtained from experiments are compared with each other. Third, repots poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/Si with rGO. The optical and electrical properties of PEDOT:PSS organic layer play a very important role in determining the power conversion efficiency (PCE) of Si-organic hybrid solar cells. In this part, properties of PEDOT:PSS thin films with rGO and their impacts on the performances of the resultant Si-organic hybrid solar cells have been systematically investigated.

Chapter III describes properties of composite hybrid SWNTs. First, 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), tetrathiafulvalene (TTF), and dodecanethiol (DoSH) were encapsulated inside SWNTs, (TCNQ@SWNT, TTF@SWNT, and DoSH@SWNT). The fourier transform infra-red (FTIR) spectra and x-ray diffraction (XRD) patterns were measured to confirm the encapsulation of organic molecules. Slight shifts of the FTIR peaks and the disappearance of an XRD peak at ~6˚, corresponding to the SWNT (10) reflection, were observed. From the measurements of the current–voltage curves, it was revealed that the current of TTF@ SWNT and DoSH@SWNT decreased, and the current of TCNQ@SWNT increased compared with that of pristine SWNTs. Second, SWNTs have strong potential for molecular electronics due to their unique structural and electronic properties. There are many advantages to encapsulation of ring structure molecules inside SWNTs. For example, improved air-stability, the bandgap energy change and charge distribution of change in SWNT, and so on. Guest ring molecules, benzene (C6H6), thiophene (C4H4S), and bezenethiol (C6H5SH) were used by encapsulation. XRD method was used to confirm encapsulation. Such a behavior clearly provides the direct proof of the charge transfer between SWNT and guest ring molecules with benzene and benzenethiol. The molecular encapsulation of benzene, thiophene and benzenethiol has been analyzed via measuring the conductivity. Currents from measuring I-V curves of encapsulated SWNTs was lower than the pristine SWNTs.|탄소나노튜브는 화학적 안정성이 뛰어나고 전기적 특성이 뛰어나 다양한 분야에 서 연구가 이루어 지고 있다. 탄소나노튜브 내부에 유기물을 담지 하거나 외부에 무기물 혹은 나노물질을 코팅하여 하이브리드 구조의 탄소나노튜브를 형성하게 될 경우에는 에너지 레벨을 조절 할 수 있게 하고 높은 전계 생성에서 매우 큰 이점을 가지게 된다. 탄소나노튜브를 기초로 하는 유무기 나노 복합체는 가스 센서, 광 검출 소자, 태양전지, 양자점 발광체 및 전계방출 소자 등에 응용이 가능하며, 유무기 물질의 특성을 동시에 이용함으로써 소자의 성능 향상에 큰 도움을 줄 수 있다. 본 연구

에서는 유무기 복합체를 이용한 탄소나노튜브를 이용하여 광/전 소자의 성능 개선에관한 연구를 기술하였다.

제 1장에서는 탄소나노튜브의 역사와 구조, 화학적/물리적/전기적 특성과 응용 분야, 그리고 본 연구의 목적에 관하여 기술 하였다.

제 2장에서는 탄소나노튜브를 이용한 태양전지에 대한 연구를 진행 하였다. 첫째로 ZnO 나노기둥에 CdS/CdSe 양자점을 합성시켜 태양전지를 제작하였습니다. CdS/CdSe 양자점 위에 탄소나노튜브를 적용하여 효율이 오른다는 것을 확인할 수 있었다. 그리고 효율 증가의 원인으로 빛 흡수율의 증가, 전자의 Life time 증가, 저항감소가 원인임을 밝혀냈다. 두 번째, 기존에 만들었던 CdS/CdSe 양자점을 이용한 태양전지에 P3HT라는 고분자를 이용한 하이브리드 태양전지를 제작하였다. P3HT에 탄소나노튜브를 단순히 섞는것과, 소니케이션과 스터링을 해준 샘플을 비교하였고, P3HT와 탄소나노튜브를 소니케이션과 스터링 해준 샘플의 효율이 더 좋은 것을 확인하였다. 세 째로, N-타입 실리콘 웨이퍼/PEDOT:PSS를 이용한 유/무기 태양전지에 대한 연구를 진행하였다. PEDOT:PSS에 Reduced Graphene oxide (rGO)를 섞어주면 효율이 증가한다는 것을 확인하였다. 효율 증가의 원인으로 빛의 흡수율 증가와 저항의 감소가 원인이라는 것을 밝혀냈다.

제 3장에서는 유/무기물질의 담지를 통한 탄소나노튜브의 특성을 파악하였다. 첫번째로, 담지를 통한 탄소나노튜브의 특성 변화에 대한 연구 결과를 기술 하였다. 첫째로 Tetrathiafulvalene (TTF), 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), Dodecanetiol (DoSH)를 탄소나노튜브에 담지 하였다. Fourier transform infra-red (FT-IR) spectra, X-ray diffraction (XRD) 측정을 통해 담지가 되었는지 여부를 확인하였으며, 전기전도도 측정을 통해 담지 된 내부분자가 전기전도도에 미치는 영향을 확인할 수 있었다. 두번째, 탄소나노튜브에 링분자 (benzene, thiophene, bezenethiol) 담지를 통한 탄소나노튜브의 전기적 특성 변화에 대한 연구 결과를 기술 하였다. 라만과 XRD의 측정을 통해 담지가 되어있음을 확인하였고, 전기 전도도 측정을 통해 담지된 분자가 어떠한 전기적 특성 변화가 나타나는지 확인하였다.

제 4장에서는 본 연구는 비교적 간단한 방법을 통해 탄소나노튜브의 특성을 변화시키고, 탄소나노튜브 복합체를 형성할수 있으며, 탄소나노튜브 복합체의 특성 변화를 확인 하였다. 또한 탄소나노튜브를 다양한 분야에 응용함으로써 소자의 특성을 개선 할 수 있으며, 다양한 소자에 응용 가능성을 제공해 주었다.; Carbon nanotubes (CNTs) have excellent electrical and chemical properties, so CNTs have been experimentally researched by many groups for application at various field such as sensor, solar cell and display. Encapsulation of organic/inorganic molecules inside CNTs can be adjusted energy level and advantage high electric field. The hybrid composite single-walled carbon nanotubes (SWNTs) have advantage of organic and inorganic material, it will be next generation material including graphene. In this thesis, hybrid composite SWNTs by encapsulation was made and their properties. In addition, SWNTs were incorporated various type of solar to electrical energy conversion devices (solar cell).

Chapter I introduces a brief history, properties of CNTs, application and purpose of the thesis

Chapter II reports application solar cell incorporating SWNTs or reduced graphene oxide (rGO). First, quantum dot-sensitized solar cells (QDSSCs) research incorporating with SWNTs were studied. QDSSCs were synthesized using CdS and CdSe quantum dots (QDs) incorporated onto one-dimensional ZnO nanorods by successive ionic layer adsorption. In order to get the highest performance of the synthesized cell, the concentration of precursor QDs solution and the number of deposition cycles in the QDs solution were varied together. The photovoltaic performance of each cell was compared with the ultraviolet/visible absorption spectra and incident photon to current efficiency graphs. QDSSCs incorporating SWNTs, sprayed onto the substrate before deposition of the next layer, exhibited enhanced or decreased photocell efficiency compared to that of the pristine cell. In particular, a maximum rate increase of 17% was obtained with the solar cell containing SWNTs in CdSe QDs. Second, hybrid-QDSSCs (h-QDSSCs) research incorporating with SWNTs were studied. Regioregular poly(3-hexylthiophene) (P3HT) is used as a material to substitute for the liquid electrolyte in the QDSSCs. In order to gain high performance of the cell, three different cells using P3HT, pristine P3HT, SWNT-mixed P3HT (mixing), and SWNT-blended P3HT (blended) are made and their photovoltaic cells measure J–V curve, incident photon to current efficiency, and electrochemical impedance spectroscopy. Those values obtained from experiments are compared with each other. Third, repots poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/Si with rGO. The optical and electrical properties of PEDOT:PSS organic layer play a very important role in determining the power conversion efficiency (PCE) of Si-organic hybrid solar cells. In this part, properties of PEDOT:PSS thin films with rGO and their impacts on the performances of the resultant Si-organic hybrid solar cells have been systematically investigated.

Chapter III describes properties of composite hybrid SWNTs. First, 7,7,8,8-tetracyano-p-quinodimethane (TCNQ), tetrathiafulvalene (TTF), and dodecanethiol (DoSH) were encapsulated inside SWNTs, (TCNQ@SWNT, TTF@SWNT, and DoSH@SWNT). The fourier transform infra-red (FTIR) spectra and x-ray diffraction (XRD) patterns were measured to confirm the encapsulation of organic molecules. Slight shifts of the FTIR peaks and the disappearance of an XRD peak at ~6˚, corresponding to the SWNT (10) reflection, were observed. From the measurements of the current–voltage curves, it was revealed that the current of TTF@ SWNT and DoSH@SWNT decreased, and the current of TCNQ@SWNT increased compared with that of pristine SWNTs. Second, SWNTs have strong potential for molecular electronics due to their unique structural and electronic properties. There are many advantages to encapsulation of ring structure molecules inside SWNTs. For example, improved air-stability, the bandgap energy change and charge distribution of change in SWNT, and so on. Guest ring molecules, benzene (C6H6), thiophene (C4H4S), and bezenethiol (C6H5SH) were used by encapsulation. XRD method was used to confirm encapsulation. Such a behavior clearly provides the direct proof of the charge transfer between SWNT and guest ring molecules with benzene and benzenethiol. The molecular encapsulation of benzene, thiophene and benzenethiol has been analyzed via measuring the conductivity. Currents from measuring I-V curves of encapsulated SWNTs was lower than the pristine SWNTs.