염료감응형 태양전지 소자의 내구성과 효율 최적화를 위한 유무기 기능성 소재의 적용. Application of organic/inorgainc functional materials to optimize durability and efficiency of dye-sensitized solar cells.원문보기
김동우
(영남대학교 대학원
화학공학과 염료감응형 태양전지(Dye Sensitized Solar Cell)
국내석사)
화석연료의 무분별한 사용으로 인해 지구온난화의 문제가 심각해지고 있으며, 신재생 에너지에 대한 관심이 높아지고 있습니다. 그중 태양광을 이용해 전력을 생산하는 태양전지의 경우 가장 이상적이며 합리적인 신 재생에너지로 여겨지고 있습니다. 하지만 기존에 상용화된 실리콘 태양전...
화석연료의 무분별한 사용으로 인해 지구온난화의 문제가 심각해지고 있으며, 신재생 에너지에 대한 관심이 높아지고 있습니다. 그중 태양광을 이용해 전력을 생산하는 태양전지의 경우 가장 이상적이며 합리적인 신 재생에너지로 여겨지고 있습니다. 하지만 기존에 상용화된 실리콘 태양전지의 경우 넓은 부지와 태양광의 입사각의 제한 때문에 70%가 산간으로 이루어진 우리나라의 국토 조건에 맞지 않으며, 도심 건물에 적용이 가능한 차세대 태양전지의 필요성이 높아졌습니다. 그중 가장 적합한 태양전지는 입사각에 영향을 적게 받으며, 여러 가지 색을 구현할 수 있는 염료감응형 태양전지입니다. 본 실험에서는 염료감응형 태양전지의 상용화를 위해 효율과 내구성을 최적화하는 실험을 진행했습니다. 효율의 경우 FRET 형태의 에너지 전달 과정을 이용했으며, 내구성의 경우 전공 운송해 층의 형성 시 열 중합 방법을 이용한 실험을 진행했습니다.
화석연료의 무분별한 사용으로 인해 지구온난화의 문제가 심각해지고 있으며, 신재생 에너지에 대한 관심이 높아지고 있습니다. 그중 태양광을 이용해 전력을 생산하는 태양전지의 경우 가장 이상적이며 합리적인 신 재생에너지로 여겨지고 있습니다. 하지만 기존에 상용화된 실리콘 태양전지의 경우 넓은 부지와 태양광의 입사각의 제한 때문에 70%가 산간으로 이루어진 우리나라의 국토 조건에 맞지 않으며, 도심 건물에 적용이 가능한 차세대 태양전지의 필요성이 높아졌습니다. 그중 가장 적합한 태양전지는 입사각에 영향을 적게 받으며, 여러 가지 색을 구현할 수 있는 염료감응형 태양전지입니다. 본 실험에서는 염료감응형 태양전지의 상용화를 위해 효율과 내구성을 최적화하는 실험을 진행했습니다. 효율의 경우 FRET 형태의 에너지 전달 과정을 이용했으며, 내구성의 경우 전공 운송해 층의 형성 시 열 중합 방법을 이용한 실험을 진행했습니다.
-1- Direct sunlight harvesting technologies using photovoltaics have received great attention as indispensable components of future global energy production. Among photovoltaic technologies, dye-sensitized solar cells (DSSCs) described by O’ä progressive solar energy conversion technology becaus...
-1- Direct sunlight harvesting technologies using photovoltaics have received great attention as indispensable components of future global energy production. Among photovoltaic technologies, dye-sensitized solar cells (DSSCs) described by O’ä progressive solar energy conversion technology because of their low cost, simple fabrication, and eco-friendliness. Intraditional DSSCs, ruthenium-based complexes (for example, N719 and Z907) are used as the sensitizing dyes (SDs). These ruthenium-based dyes have wide absorption spectra (Δλ≈ 20,000 M−1cm−1). With relatively low molar extinction coefficients, thick layers of mesoporous TiO2 are required to increase dye-loading to achieve good light-harvesting. Therefore, the cost of the DSSCs increases and the flexibility decreases. In contrast, organic dyes have high molar extinction coefficients (50,000-200,000 M−1cm−1), but very narrow absorption spectra (Δλ≈ To enhance light harvesting and conversion efficiency, absorption across the wide solar spectrum is required. To enhance light absorption and broaden the spectral response for organic DSSCs, several approaches have been introduced such as cosensitization by dyes with complementary absorption spectra dyes, quantum-dots, cascade cells, and tandem cells. However, co-sensitization by dyes limits the number of available sites on the surface of the semiconductor nanoparticles. Tandem cells require an elaborate production process, and numerous limitations. Alternatively, an extensively used molecular engineering method to increase dye efficiency by increasing the amount of absorbed light by loading dyes, which collect photons and redirect the captured energy via long-range energy transfer is known as Förster resonance energy transfer(FRET). Recently, FRET has been widely studied as a promising method for enhancing broad spectral responses of various chromophores. FRET is a nonradioactive energy transfer process, and is based on dipole-dipole coupling between different chromophores. Donor chromophores are initially excited by incident light, which is followed by an energy transfer to an acceptor chromophore; the efficiency of an energy transfer is affected by the distance between each molecule. Generally, FRET using quantum dots (QDs) results in high molar extinction coefficients and broad absorption spectra. However, QD FRET exhibits low power conversion efficiencies and is limited by the dye selection. On the other hand, FRET using organic fluorescent materials (FM) has many advantages including low cost, diversity of absorption and emission regions, and easy synthesis. DSSCs using liquid electrolytes containing I−/I−3 redox couple are a relatively low-cost and high-efficiency photovoltaic technology. Unfortunately, pristine liquid electrolytes based on iodide in DSSCs present several technological problems, such as volatility, permeability, dye desorption, and corrosion. These issues can be prevented by replacing the liquid electrolyte with a solid or quasi-solid state hole transport material. For this reason, solid DSSCs have attracted increasing attention as next generation solar cells owing to their high stability, simple structure, low-cost manufacturing process, and promising energy conversion efficiency. In the present study, quasi-solid state DSSCs were fabricated based on FRET process. The photovoltaic performance of the DSSC (schematically shown in Figure 1.1) was investigated using well matched energy donor and energy acceptor. An organic FM, 2,2':5',2" terthiophene, is added to the quasi-solid electrolyte. To investigate the effect of amount of FM, quasi-solid electrolyte is blended with different amounts of FM donor. As a photosensitizing acceptor, a YD-2 porphyrin dye is employed. This dye shows strong absorption and emission in the visible region as well as tunable redox potentials. The YD-2 porphyrin sensitizer can absorb photons in the range of 400-500 nm. It is expected that the fluorescence emitted by FM, which is excited by the irradiation in the 300 and 400 nm range, can generate additional electrons for the YD-2 porphyrin sensitizer. Thus, highly efficient, FRET-enhanced, quasi-solid state DSSCs can be obtained from the combination of FM and YD-2 porphyrin sensitizer as the energy donor and acceptor, respectively. -2- Dye-sensitized solar cells (DSSCs) unlocked a new perspective in the world of solar energy since the first report by O’Regan and Gratzel. The maximum energy conversion efficiency of DSSCs up to 13% has been achieved by using ruthenium dye as the sensitizer and liquid electrolyte with redox couple. The great success of DSSCs unlocks the space for its scaling up and marketable applications. Nevertheless, numerous practical problems are related to the stability of DSSCs, evaporation, and leakage of liquid. Therefore, numerous effects have made to reduce these technical limitations by replacing conventional liquid electrolytes with inorganic p-type semiconductors or organic hole transporting materials (HTMs) in the all solid-state DSSCs(ssDSSCs). The organic p-type conducting polymers have been rigorously investigated because of their low cost, good thermal stability, great conductivity, good solubility as well as simple fabrication procedure. But, have a disadvantage like low energy conversion efficiencies because of weak penetration of conductive polymers into the nanopores of TiO2 layers. In the present work, high efficient and enhanced inter facial properties by solid state polymerization of a con- ducting polymer. Here, a conductive polymer was synthesized by a brominated 3,4-ethylenedioxythiophene (EDOT) because of its effective polymerization, low cost of preparation, simple synthesis process, easily polymerizable by heating, and good solubility. There, the Dibromo-EDOT was synthesized by the common bromination method, and it transpires only in the crystal state because of the short Br ions among monomers . This crystalline Dibromo- EDOT is sufficient to penetrate through to the nanopores of nanocrystalline TiO2 layers short of any additives. The conductivity of the polymerized EDOT without using any additives at room temperature reached larger value, which is greater than chemically polymerized EDOT. This larger conductivity of polymerized EDOT perhaps contributed due to the doping of Br3− during polymerization. Consequently, polymerized EDOT with larger conductivity possibly the best candidate as an HTM. This work also studies different molar ratios of polymerized EDOT as an HTM to the corresponding cell efficiencies of the ssDSSCs are examined. -3- The demand for renewable energy becomes more significant from the last few decades. In the race of renewable energies, the dye-sensitized solar cells (DSSCs) were introduced in 1991 by Gratzel group have been electrifying solar cell research area, because of their counterparts in terms of flexibility, ease of fabrication, light weight, and low-cost [1]. In traditional DSSCs, TiO2 as a semiconductor, ruthenium-based complexes as a dye, and liquid electrolytes associated with the redox couple have been reported to exhibit high efficiency 13% [2]; and Triarylamine dye-based DSSC have exceeded to 14% [3]. Indeed, technical fabrication inadequacies in DSSCs like sealing of cell, lack of long-term durability, and inflexibility due to liquid electrolyte. So, the best alternative to overcome its drawbacks is the replacement of the liquid redox electrolyte with solid counterpart’s like ionically conductive gels, p-type inorganic materials, molecular or macromolecular organic hole conductors [4-9]. Therefore, this research area has been interest, and highly attractive to industrial production and partial application as a new third generation solid- state dye-sensitized solar cells (ssDSSCs). In this regard, the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is widely used as a hole transporting material (HTM) because it has many advantages like high transparency, smooth morphology, good hole conductivity, and high work function. However, PEDOT: PSS has several disadvantages like, less penetration depth into TiO2 layer, degradation under UV light, highly acidic, an inefficient electron-blocking layer, hygroscopic nature, and high series resistance [10-12]. Substituting PEDOT:PSS by the most stable HTM is therefore a feasible choice for good ssDSSCs. The HTM should be easily synthetically accessible, good solubility, excellent electron blocking and hole transporting properties. Therefore, in this work, a brominated 3,4-ethylenedioxythopene (Dibromo-EDOT) is
selected as the conductive polymer because of its low cost of synthesis, easy preparation, excellent polymerization, high conductivity, easy penetration through nano-pores of TiO2, and easy polymerization by heating without additives [13]. To further increase the performance of ssDSSC device and also blocking electron efficiently in HTM by using the inorganic transition metal oxides such as MoO3 [14, 15], NiO [16], V2O5 [17], and WO3 [18]. These materials are successfully studied as inorganic HTM for DSSCs, perovskite solar cells, and also for organic light-emitting diodes. Among, these materials, MoO3 is one of best promising material due to the presence of wide band gaps in its electronic states that can be efficiently blocks electron, nontoxic nature, and it is also improves the performance of the cells [19, 20]. Considering the benefits of both these polymer and inorganic HTM materials, in this present work, we investigate the photovoltaic properties of ssDSSCs with a hybrid HTM (polymer /inorganic) material. However, the inorganic-organic interface has rapt helpfulness to increase device efficiency by diminishing charge injection/extraction barriers. The hybrid HTMs were chosen as 1 wt% conducting polymerized Dibromo-EDOT and different wt% of nanocrystalline MoO3. As per our knowledge, the hybrid HTM was prepared first time with the combination of nanocrystalline MoO3 and conducting polymerized Dibromo-EDOT for fabrication of ssDSSCs. In this work, we thoroughly investigated the ssDSSCs by hybrid HTM with increasing wt% of nanocrystalline MoO3 from 0.2 to 0.6, and their corresponding device perform is compared.
-1- Direct sunlight harvesting technologies using photovoltaics have received great attention as indispensable components of future global energy production. Among photovoltaic technologies, dye-sensitized solar cells (DSSCs) described by O’ä progressive solar energy conversion technology because of their low cost, simple fabrication, and eco-friendliness. Intraditional DSSCs, ruthenium-based complexes (for example, N719 and Z907) are used as the sensitizing dyes (SDs). These ruthenium-based dyes have wide absorption spectra (Δλ≈ 20,000 M−1cm−1). With relatively low molar extinction coefficients, thick layers of mesoporous TiO2 are required to increase dye-loading to achieve good light-harvesting. Therefore, the cost of the DSSCs increases and the flexibility decreases. In contrast, organic dyes have high molar extinction coefficients (50,000-200,000 M−1cm−1), but very narrow absorption spectra (Δλ≈ To enhance light harvesting and conversion efficiency, absorption across the wide solar spectrum is required. To enhance light absorption and broaden the spectral response for organic DSSCs, several approaches have been introduced such as cosensitization by dyes with complementary absorption spectra dyes, quantum-dots, cascade cells, and tandem cells. However, co-sensitization by dyes limits the number of available sites on the surface of the semiconductor nanoparticles. Tandem cells require an elaborate production process, and numerous limitations. Alternatively, an extensively used molecular engineering method to increase dye efficiency by increasing the amount of absorbed light by loading dyes, which collect photons and redirect the captured energy via long-range energy transfer is known as Förster resonance energy transfer(FRET). Recently, FRET has been widely studied as a promising method for enhancing broad spectral responses of various chromophores. FRET is a nonradioactive energy transfer process, and is based on dipole-dipole coupling between different chromophores. Donor chromophores are initially excited by incident light, which is followed by an energy transfer to an acceptor chromophore; the efficiency of an energy transfer is affected by the distance between each molecule. Generally, FRET using quantum dots (QDs) results in high molar extinction coefficients and broad absorption spectra. However, QD FRET exhibits low power conversion efficiencies and is limited by the dye selection. On the other hand, FRET using organic fluorescent materials (FM) has many advantages including low cost, diversity of absorption and emission regions, and easy synthesis. DSSCs using liquid electrolytes containing I−/I−3 redox couple are a relatively low-cost and high-efficiency photovoltaic technology. Unfortunately, pristine liquid electrolytes based on iodide in DSSCs present several technological problems, such as volatility, permeability, dye desorption, and corrosion. These issues can be prevented by replacing the liquid electrolyte with a solid or quasi-solid state hole transport material. For this reason, solid DSSCs have attracted increasing attention as next generation solar cells owing to their high stability, simple structure, low-cost manufacturing process, and promising energy conversion efficiency. In the present study, quasi-solid state DSSCs were fabricated based on FRET process. The photovoltaic performance of the DSSC (schematically shown in Figure 1.1) was investigated using well matched energy donor and energy acceptor. An organic FM, 2,2':5',2" terthiophene, is added to the quasi-solid electrolyte. To investigate the effect of amount of FM, quasi-solid electrolyte is blended with different amounts of FM donor. As a photosensitizing acceptor, a YD-2 porphyrin dye is employed. This dye shows strong absorption and emission in the visible region as well as tunable redox potentials. The YD-2 porphyrin sensitizer can absorb photons in the range of 400-500 nm. It is expected that the fluorescence emitted by FM, which is excited by the irradiation in the 300 and 400 nm range, can generate additional electrons for the YD-2 porphyrin sensitizer. Thus, highly efficient, FRET-enhanced, quasi-solid state DSSCs can be obtained from the combination of FM and YD-2 porphyrin sensitizer as the energy donor and acceptor, respectively. -2- Dye-sensitized solar cells (DSSCs) unlocked a new perspective in the world of solar energy since the first report by O’Regan and Gratzel. The maximum energy conversion efficiency of DSSCs up to 13% has been achieved by using ruthenium dye as the sensitizer and liquid electrolyte with redox couple. The great success of DSSCs unlocks the space for its scaling up and marketable applications. Nevertheless, numerous practical problems are related to the stability of DSSCs, evaporation, and leakage of liquid. Therefore, numerous effects have made to reduce these technical limitations by replacing conventional liquid electrolytes with inorganic p-type semiconductors or organic hole transporting materials (HTMs) in the all solid-state DSSCs(ssDSSCs). The organic p-type conducting polymers have been rigorously investigated because of their low cost, good thermal stability, great conductivity, good solubility as well as simple fabrication procedure. But, have a disadvantage like low energy conversion efficiencies because of weak penetration of conductive polymers into the nanopores of TiO2 layers. In the present work, high efficient and enhanced inter facial properties by solid state polymerization of a con- ducting polymer. Here, a conductive polymer was synthesized by a brominated 3,4-ethylenedioxythiophene (EDOT) because of its effective polymerization, low cost of preparation, simple synthesis process, easily polymerizable by heating, and good solubility. There, the Dibromo-EDOT was synthesized by the common bromination method, and it transpires only in the crystal state because of the short Br ions among monomers . This crystalline Dibromo- EDOT is sufficient to penetrate through to the nanopores of nanocrystalline TiO2 layers short of any additives. The conductivity of the polymerized EDOT without using any additives at room temperature reached larger value, which is greater than chemically polymerized EDOT. This larger conductivity of polymerized EDOT perhaps contributed due to the doping of Br3− during polymerization. Consequently, polymerized EDOT with larger conductivity possibly the best candidate as an HTM. This work also studies different molar ratios of polymerized EDOT as an HTM to the corresponding cell efficiencies of the ssDSSCs are examined. -3- The demand for renewable energy becomes more significant from the last few decades. In the race of renewable energies, the dye-sensitized solar cells (DSSCs) were introduced in 1991 by Gratzel group have been electrifying solar cell research area, because of their counterparts in terms of flexibility, ease of fabrication, light weight, and low-cost [1]. In traditional DSSCs, TiO2 as a semiconductor, ruthenium-based complexes as a dye, and liquid electrolytes associated with the redox couple have been reported to exhibit high efficiency 13% [2]; and Triarylamine dye-based DSSC have exceeded to 14% [3]. Indeed, technical fabrication inadequacies in DSSCs like sealing of cell, lack of long-term durability, and inflexibility due to liquid electrolyte. So, the best alternative to overcome its drawbacks is the replacement of the liquid redox electrolyte with solid counterpart’s like ionically conductive gels, p-type inorganic materials, molecular or macromolecular organic hole conductors [4-9]. Therefore, this research area has been interest, and highly attractive to industrial production and partial application as a new third generation solid- state dye-sensitized solar cells (ssDSSCs). In this regard, the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is widely used as a hole transporting material (HTM) because it has many advantages like high transparency, smooth morphology, good hole conductivity, and high work function. However, PEDOT: PSS has several disadvantages like, less penetration depth into TiO2 layer, degradation under UV light, highly acidic, an inefficient electron-blocking layer, hygroscopic nature, and high series resistance [10-12]. Substituting PEDOT:PSS by the most stable HTM is therefore a feasible choice for good ssDSSCs. The HTM should be easily synthetically accessible, good solubility, excellent electron blocking and hole transporting properties. Therefore, in this work, a brominated 3,4-ethylenedioxythopene (Dibromo-EDOT) is
selected as the conductive polymer because of its low cost of synthesis, easy preparation, excellent polymerization, high conductivity, easy penetration through nano-pores of TiO2, and easy polymerization by heating without additives [13]. To further increase the performance of ssDSSC device and also blocking electron efficiently in HTM by using the inorganic transition metal oxides such as MoO3 [14, 15], NiO [16], V2O5 [17], and WO3 [18]. These materials are successfully studied as inorganic HTM for DSSCs, perovskite solar cells, and also for organic light-emitting diodes. Among, these materials, MoO3 is one of best promising material due to the presence of wide band gaps in its electronic states that can be efficiently blocks electron, nontoxic nature, and it is also improves the performance of the cells [19, 20]. Considering the benefits of both these polymer and inorganic HTM materials, in this present work, we investigate the photovoltaic properties of ssDSSCs with a hybrid HTM (polymer /inorganic) material. However, the inorganic-organic interface has rapt helpfulness to increase device efficiency by diminishing charge injection/extraction barriers. The hybrid HTMs were chosen as 1 wt% conducting polymerized Dibromo-EDOT and different wt% of nanocrystalline MoO3. As per our knowledge, the hybrid HTM was prepared first time with the combination of nanocrystalline MoO3 and conducting polymerized Dibromo-EDOT for fabrication of ssDSSCs. In this work, we thoroughly investigated the ssDSSCs by hybrid HTM with increasing wt% of nanocrystalline MoO3 from 0.2 to 0.6, and their corresponding device perform is compared.
주제어
#functional materials dye-sensitized solar cells DSSCs MoO3 FRET
학위논문 정보
저자
김동우
학위수여기관
영남대학교 대학원
학위구분
국내석사
학과
화학공학과 염료감응형 태양전지(Dye Sensitized Solar Cell)
지도교수
김재홍
발행연도
2019
총페이지
61
키워드
functional materials dye-sensitized solar cells DSSCs MoO3 FRET
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