成果報告書詳細
管理番号20120000000371
タイトル*平成23年度中間年報 太陽エネルギー技術研究開発 太陽光発電システム次世代高性能技術の開発 三層協調界面構築による高効率・低コスト・量産型色素増感太陽電池の研究開発(高効率化技術及びメカニズム解析に関する研究開発)
公開日2012/12/4
報告書年度2011-2011
委託先名国立大学法人信州大学
プロジェクト番号P07015
部署名新エネルギー部
和文要約和文要約等以下本編抜粋
高効率色素増感太陽電池を実現するための要素として、前年度に引き続き反応エネルギー制御色素の開発を行った。Black Dyeの高効率化を目的とし、ターピリジン配位子の非対称化および機能性団の導入を系統的に行ったところBlack Dyeよりも高い電流値が得られ、かつ高電圧化への指針が得られた。高効率セルの作製においては反応エネルギーを低減できるコバルト錯体レドックス対と新規有機色素を用い、酸化チタン電極の構造を最適化することで8.3%の変換効率が得られた。また反応エネルギーを下げる目的で、酸化チタンの結晶面やサイズを制御した粒子から電極を作製し、再結合速度とトラップ密度を測定し、かつ活性化エネルギーを見積もったところ特徴があることが分かった。
英文要約Abstract for FY2011
A new series of ruthenium(II) sensitizers for dye-sensitized solar cells (DSSCs) derived from asymmetric terpyridyl complexes possessing different substituents on each pyridine in terpyridine ligand have been developed. A new asymmetric terpyridine ligand 1, in which two carboxylic acids are attached with two pyridines and the other pyridine has one bromide as a connection point to introduce functional units through palladium-catalyzed cross-coupling reactions, was developed as a molecular platform for systematic design of panchromatic ruthenium(II) sensitizers. The introduction of substituents into terpyridine ligand would enhance the efficiency in the dye-sensitized solar cells due to the expansion of light-absorb region and the control of light-induced electron transfer process at the interface of TiO2-dye-redox electrolyte. From this ligand, we synthesized a new series of panchromatic ruthenium complexes MJ-4, MJ-6, MJ-7, MJ-8, and MJ-9 possessing different functional units. The attachment of functional units into the dicarboxy terpyridine ligand affected the characteristic MLCT transition of ruthenium complexes. The performances of dye-sensitized solar cells using these ruthenium complexes depended on the structure of functional units. The MJ-6 cell showed almost the same performance of N749 cell fabricated under similar conditions due to higher short-circuit current. On the other hand, open circuit voltage was lower than that with N749 cell. In order to obtain high Voc, we designed several dyes by attaching alkyl chains to MJ-6, and synthesis and evaluation is in progress.
In order to increase the energy conversion efficiency, energies needed for electron transfer are minimized. For the case of charge injection, 0.2 eV difference between the conduction band edge potential and LUMO level of sensitizers is generally needed. The difference could be due to the inhomogeneity of crystal facet of the nano-particles. Therefore, we prepared solar cells from nano-particles having mostly only one facet. From injection kinetic measurements, there seems to be difference depending on the crystal surface while it was hardly seen in the solar cells performance. Thus we are studying now with dyes having smaller energy difference between the conduction band and LUMO of senstizers.
Another interface requiring large energy for charge transfer is between dye and electrolyte. To reduce the difference, we study the combination of various dyes and cobalt redox couples. With bulky organic dyes, such as MK2, MK24, and MK34, and a cobalt redox couple, we have achieved 8.3% efficiency. For further development, pore size of TiO2 electrode and reduction kinetics should be optimized.
To reduce dye cation after electron injection to TiO2, required energy between the HOMO level of dyes and redox potential of redox couple is generally 0.5 to 0.6 eV. This energy difference also depends on the structure of dyes. To obtain design guide for sensitizers, we studied reduction kinetics for various dyes. So far we found that the structure of donor and length of linker bridge influences on the reduction kinetics. We will study further to obtain complete view for the kinetics and will design dyes based on the findings.
The construction of sub-nano second transient absorption measurement system combined with transient photovoltaic measurement was started. The optical system was optimized to obtain sufficient signal to noise ratio.
The 10 newly developed dyes from the members of the consortium have been analyzed with photovoltaic and spectroscopic measurements. The resultant lower open circuit voltage than commercial dyes was attributed to the higher recombination rate or lower amount of adsorbed dye. We feedback such findings to the members to develop dyes further.
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