Role of the Charge-Transfer State in Reduced Langevin Recombination in Organic Solar Cells: A Theoretical Study

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• 作者：Yiming Liu ; Karin Zojer ; Benny Lassen ; Jakob Kjelstrup-Hansen ; Horst-G眉nter Rubahn ; Morten Madsen
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：November 25, 2015
• 年：2015
• 卷：119
• 期：47
• 页码：26588-26597
• 全文大小：506K
• ISSN：1932-7455

文摘

Reduced Langevin recombination has been observed in organic solar cells (OSCs) for many years, but its origin is still unclear. A recent work by Burke et al. ( Adv. Energy Mater. 2015, 5, 1500123-1) was inspired by this reduced Langevin recombination, and they proposed an equilibrium model of charge-transfer (CT) states that correlates the open-circuit voltage of OSCs with experimentally available device parameters. In this work, we extend Burke et al.鈥檚 CT model further and for the first time directly correlate the reduced Langevin recombination with the energetic and dynamic behavior of the CT state. Recombination through CT states leads in a straightforward manner to a decrease in the Langevin reduction factor with increasing temperature, without explicit consideration of the temperature dependence of the mobility. To verify the correlation between the CT states and reduced Langevin recombination, we incorporated this CT model and the reduced Langevin model into drift-diffusion simulations of a bilayer OSC. The simulations not only successfully reproduced realistic current鈥搗oltage (J鈥?i>V) characteristics of the bilayer OSC, but also demonstrate that the two models consistently lead to same value of the apparent Langevin reduction factor.