복합 산화/환원 전해질 및 전극과의 계면

Abstract

우수한 가격경쟁력을 지닌 염료감응 태양전지는, 그 효율은 이론치인 20%에 크게 미치지 못하는 수준이다. 그 문제점은, 1) 전하 전달간의 전압소실, 2) 흡광 및 광전변환 소실, 3) 저항으로 인한 전자 이동간의 소실이다. 상기 문제를 해결을 위해, 전해질과 전극을 주제로 학위 논문 연구를 진행하였다. 이에 대한 연구 결과는 챕터 2‒7에 소개된다. 일단, 첫 파트에서는 염료감응 태양전지 대한 소개를 다룬다. 두번째 파트에서는, 염료감응 태양전지에서의 복합 산화/환원 전해질에 대한 내용이다. 특히, 챕터 2에서는 새로운 I-/(SeCN)2 산화/환원 전해질에 개발을 포함한다. 챕터 3에서는, 고분자 전해질 에서의 주석산화 나노 입자의 화학적 영향에 대한 내용을 담고 있다. 챕터 4에서는, 염료감응 태양전지에서 고분자 전해질 연구 방향을 아우른다. 세번째 파트에서는, 염료감응 태양전지에서 광전극 개발 및 계면 분석에 대한 내용을 포함한다. 챕터 5‒6에서는 tetraethyl orthosilicate의 두가지 기능을 다루는데, 그 하나는 평형 반응 시프트 매개체, 다른 하나는 전극 보호막으로써의 역할이다. 챕터 7에서는, 전자 이동능이 우수한 3차원 그라핀 기반 광전극 개발에 대한 연구 결과를 포함한다. 마지막 파트에서는, 고효율 고분자 전해질 염료감응 태양전지 개발을 위해, 선행 연구된 전해질, 전극 혹은 전해질/전극간의 최적화를 위한 연구방향을 토의한다.|Since the pioneer work (~7% reported) in 1991 by O’Regan and Grätzel, dye-sensitized solar cells (DSCs) have shown promise as a cost competitive photovoltaics. Currently, record efficiency of 13% is reported in the DSCs, but still falling short of their theoretically achievable efficiency of ~20%. Obstructive factors for the maximum efficiency could be categorized according by such 1) loss-in-potential for charge transfer, 2) incomplete light harvest and conversion in a non-optimal wavelength range, and 3) resistive losses for charge transport. This dissertation comprises 9 Chapters. Chapter 1 is Introduction, where funadamental and basics for photovoltaics is briefly described. In addition, the concept on electrochemical impedance spectroscopy is also introduced. Chapters 2‒4 are on hybridized redox electrolyte and perspective on polymer electrolyte for DSCs. In Chapter 2, it is attempted to attenuate the potential-loss of ~ 0.3 eV for dye regeneration with the I-/I3- redox couple. In this regard, the (SeCN)2 species coupled with I- species are developed. In Chapter 3, chemical effects of metal oxide NPs (SnO2 NPs) in PEO polymer electrolyte are demonstrated. The acidic surface of SnO2 NPs may electrostatically interact with anionic charges like I-, I3- or oxygen in the PEO polymer electrolyte and outwardly with cationic (counter) charges like Li+ or K+ for electroneutrality, analogous to the formation of electrical double layer. This localization of ion species may lessen the concentration of both anion and cation in the TiO2 mesopore, resulting in the reduced electron recombination by less [I3-] and the less downward TiO2 conduction band edge shift by less [K+], with the increase in the diffusion coefficient of I3-. Meanwhile, hurdles left behind solid state DSCs employing polymer electrolytes are dealted in Chpater 5. Tremendous preliminary results imply that a major bottleneck to be tied-up at 8.9% device efficiency is closely associated with both the poor ion diffusion and the poor TiO2 pore filling by redox electrolyte. In order to avoid/relieve these negative cases, three device design routes are introduced and discussed. Discussion on development of photoelectrodes and their interfaces is proceeded in Chapters 5‒7. Chapters 5‒6 present the dual functionality of tetraethyl orthosilicate (TEOS) as a passivation layer and as an equilibrium shifting agent. In Chapter 5, the facile strategy to repair the pinhole defects is explored by passivating them with siloxanes coadsorbents. The formation of densely packed passivation layers leads to more than 5-fold longer electron life time and 11% improved energy conversion efficiency. In Chapter 6, TEOS is used as an equilibrium shifting agent, so as to bias the equilibrium reaction to enhance the ester bond formation. This concept suggests how we can enhance the stability as well as the performance of the organic solar device. In Chapter 7, unprecedented, three dimensional TiO2 network hybridized with continuous mono-layered graphene of exhibiting high quality and transparency is demonstrated for use in DSCs for the first time to our best knowledge. Charge collection efficiency is significiantly improved by the 3D continuous pathway for electrons due to the graphene’s energetically and kinetically favorable properties. In conclusion, fusion is emphasized for highly efficient soild polymer DSC because DSC is an output of interdisciplinary fields dealing with both organic and inorganic compounds. The maximum theoretical efficiency of ~30% could be realized by optimizing the energetic and kinetic properties of each component, developed so far, in the near future.; Since the pioneer work (~7% reported) in 1991 by O’Regan and Grätzel, dye-sensitized solar cells (DSCs) have shown promise as a cost competitive photovoltaics. Currently, record efficiency of 13% is reported in the DSCs, but still falling short of their theoretically achievable efficiency of ~20%. Obstructive factors for the maximum efficiency could be categorized according by such 1) loss-in-potential for charge transfer, 2) incomplete light harvest and conversion in a non-optimal wavelength range, and 3) resistive losses for charge transport. This dissertation comprises 9 Chapters. Chapter 1 is Introduction, where funadamental and basics for photovoltaics is briefly described. In addition, the concept on electrochemical impedance spectroscopy is also introduced. Chapters 2‒4 are on hybridized redox electrolyte and perspective on polymer electrolyte for DSCs. In Chapter 2, it is attempted to attenuate the potential-loss of ~ 0.3 eV for dye regeneration with the I-/I3- redox couple. In this regard, the (SeCN)2 species coupled with I- species are developed. In Chapter 3, chemical effects of metal oxide NPs (SnO2 NPs) in PEO polymer electrolyte are demonstrated. The acidic surface of SnO2 NPs may electrostatically interact with anionic charges like I-, I3- or oxygen in the PEO polymer electrolyte and outwardly with cationic (counter) charges like Li+ or K+ for electroneutrality, analogous to the formation of electrical double layer. This localization of ion species may lessen the concentration of both anion and cation in the TiO2 mesopore, resulting in the reduced electron recombination by less [I3-] and the less downward TiO2 conduction band edge shift by less [K+], with the increase in the diffusion coefficient of I3-. Meanwhile, hurdles left behind solid state DSCs employing polymer electrolytes are dealted in Chpater 5. Tremendous preliminary results imply that a major bottleneck to be tied-up at 8.9% device efficiency is closely associated with both the poor ion diffusion and the poor TiO2 pore filling by redox electrolyte. In order to avoid/relieve these negative cases, three device design routes are introduced and discussed. Discussion on development of photoelectrodes and their interfaces is proceeded in Chapters 5‒7. Chapters 5‒6 present the dual functionality of tetraethyl orthosilicate (TEOS) as a passivation layer and as an equilibrium shifting agent. In Chapter 5, the facile strategy to repair the pinhole defects is explored by passivating them with siloxanes coadsorbents. The formation of densely packed passivation layers leads to more than 5-fold longer electron life time and 11% improved energy conversion efficiency. In Chapter 6, TEOS is used as an equilibrium shifting agent, so as to bias the equilibrium reaction to enhance the ester bond formation. This concept suggests how we can enhance the stability as well as the performance of the organic solar device. In Chapter 7, unprecedented, three dimensional TiO2 network hybridized with continuous mono-layered graphene of exhibiting high quality and transparency is demonstrated for use in DSCs for the first time to our best knowledge. Charge collection efficiency is significiantly improved by the 3D continuous pathway for electrons due to the graphene’s energetically and kinetically favorable properties. In conclusion, fusion is emphasized for highly efficient soild polymer DSC because DSC is an output of interdisciplinary fields dealing with both organic and inorganic compounds. The maximum theoretical efficiency of ~30% could be realized by optimizing the energetic and kinetic properties of each component, developed so far, in the near future.