Development of innovative solar cells based on bulk photovoltaic effect of ferroelectric pi-conjugated liquid crystals

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01904
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 32020:Functional solid state chemistry-related
• Research Institution: Kagawa University
• Principal Investigator: Funahashi Masahiro 香川大学, 創造工学部, 教授 (90262287)
• Co-Investigator(Kenkyū-buntansha): 上村 忍 香川大学, 創造工学部, 教授 (60423498)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: バルク光起電力効果 / 有機半導体 / 強誘電性液晶 / キラリティー / 液晶製半導体 / オリゴチオフェン / 乳酸エステル

Outline of Final Research Achievements

We studied a bulk photovoltaic effect in ferroelectric liquid crystals based on extended pi-conjugated units. We synthesized ferroelectric liquid crystals bearing a quinquethiophene unit. The quinquethiophene derivative bearing a lateral methyl group at 4-position exhibited an ordered ferroelectric smectic phase in which a polarization can be immobilized by DC bias application. Photovoltaic effect was observed for white light illumination in the liquid crystal doped with PCBM in 11 mol%. Th open-circuit voltage was 0.72 V while fill factor exceeded 0.7 and power conversion efficiency was 0.7 %. The absorption edge was shifted to 580 nm and visible light energy could be utilized more efficiently than the ferroelectric liquid crystals comprising shorter pi-conjugated units.

Free Research Field

有機機能化学

Academic Significance and Societal Importance of the Research Achievements

従来の接合型太陽電池のエネルギー変換効率の理論限界は32％程度と言われている。この値を超えるためには従来の接合型太陽電池とは異なった原理の光起電力素子の開発が必要となる。強誘電体の自発分極を駆動力とするバルク光起電力効果が注目されているが、有機物の例は非常に限られており、室温でμA/cm2以上の電流密度と1 V以上の開放電圧を実現した例はない。本研究課題では、強誘電性液晶を用いたバルク光起電力効果を検討し、最大で数百μA/cm2の電流密度、1.2 Vの開放電圧を実現した。拡張π電子共役系を組み込んだ強誘電性液晶の光起電力材料としての有効性を立証することができた。