Hole Transport in Diketopyrrolopyrrole (DPP) Small Molecules: A Joint Theoretical and Experimental Study

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• 作者：Zi Li ; Xu Zhang ; Yuan Zhang ; Cristiano F. Woellner ; Martijn Kuik ; Jianhua Liu ; Thuc-Quyen Nguyen ; Gang Lu
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：April 4, 2013
• 年：2013
• 卷：117
• 期：13
• 页码：6730-6740
• 全文大小：508K
• 年卷期：v.117,no.13(April 4, 2013)
• ISSN：1932-7455

文摘

Charge transport in 3,6-bis[5-(benzofuran-2-yl)thiophen-2-yl]-2,5-bis(2-ethylhexyl)pyrrolo[3,4-c]pyrrole-1,4-dione [DPP(TBFu)₂] small molecules, a model donor material for organic photovoltaics, is studied by combined first-principles simulations and experiments. The dependence of the hole mobility on electric field, temperature, and molecular packing is examined in detail. Phonon-assisted hole transition rates and energetic disorder are identified as key intrinsic factors that control the hole mobility in DPP small molecules, with the latter playing a more important role than the former. In order to explain the substantial mobility differences between the as-cast and annealed films, we examine the effect of energetic traps on charge transport. For a trapping energy of 0.4 eV and a trap density of 1.5 脳 10¹⁷/cm³, we find that 98% of the carriers are trapped and the mobility drops by 2 orders of magnitude. With trap densities of 4.5 脳 10¹⁸/cm³ and 1.5 脳 10¹⁷/cm³ and trapping energy of 0.4 eV, we can reproduce the experimental mobilities for the as-cast and annealed films, respectively. Finally, we speculate on possible molecular defects that could act as traps for the holes.