Potential Barrier and Excess Energy for Electron鈥揌ole Separation from the Charge-Transfer Exciton at Donor鈥揂cceptor Heterojunctions of Organic Solar Cells

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• 作者：Hiroyuki Tamura ; Irene Burghardt
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：July 25, 2013
• 年：2013
• 卷：117
• 期：29
• 页码：15020-15025
• 全文大小：339K
• 年卷期：v.117,no.29(July 25, 2013)
• ISSN：1932-7455

文摘

The mechanism of electron鈥揾ole separation overcoming Coulomb attraction is one of the important open questions related to the efficiency of organic solar cells. In this work, we have theoretically predicted the potential curves for electron鈥揾ole separation from the bound charge-transfer (CT) state at donor鈥揳cceptor heterojunctions. The electron鈥揾ole potential was calculated considering an oligothiophene鈥揻ullerene donor鈥揳cceptor complex using the long-range-corrected density functional theory. The screening effect of the medium was taken into account by scaling with the dielectric constants of fullerene and polythiophene. The potential barrier was found to decrease as the 蟺-conjugation length of the donor increased. We propose a simple analytical formula for the Coulomb potential between an electron localized at a fullerene molecule and a hole distributed along a 蟺-conjugated chain. We also discuss the possible role of the excess energy due to the preceding exciton dissociation in facilitating the charge separation.