Limits on the Fill Factor in Organic Photovoltaics: Distinguishing Nongeminate and Geminate Recombination Mechanisms

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• 作者：George F. A. Dibb ; Fiona C. Jamieson ; Andrea Maurano ; Jenny Nelson ; James R. Durrant
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2013
• 出版时间：March 7, 2013
• 年：2013
• 卷：4
• 期：5
• 页码：803-808
• 全文大小：300K
• 年卷期：v.4,no.5(March 7, 2013)
• ISSN：1948-7185

文摘

In this Letter, we present transient optoelectronic experimental studies of the recombination processes limiting the fill factor (FF) in three conjugated polymer:fullerene systems, poly(3-hexylthiophene) (P3HT) and two lower-band-gap polymers that exhibit lower FFs poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b鈥瞉dithiophene)-alt-4,7-(2,1,3-benzothiadiazole) (PCPDTBT) and poly(2,7-(9,9-dioctylfluorene)-alt-5,5-(4鈥?7鈥?di-2-thienyl-2鈥?1鈥?3鈥?benzothiadiazole)) (APFO-3). Using transient absorption spectroscopy, charge extraction, and transient photovoltage experiments, we show that the lower FF observed for the PCPDTBT-based device results from enhanced nongeminate recombination even at short circuit, In contrast, we show that for APFO-3 devices, the FF is primarily limited by a voltage-dependent free charge generation, which we assign to a geminate recombination process.

Keywords:

organic solar cells; recombination; fill factor; bulk heterojunction; nongeminate