Percolative Charge Transport in Organic Semiconductor Devices with Host-Guest Layers.

Abstract

In organic semiconductor devices with a host-guest active layer, guest molecules can transport charges by forming conductive filamentary paths once their concentration exceeds a critical threshold. However, distinguishing this <i>percolative transport</i>─or percolation─from overall charge movements presents a formidable challenge. Here, we introduce an organic unipolar host-guest device wherein charge transport occurs <i>exclusively</i> through guest molecules, i.e., percolation, while the hosts remain electrically inactive. This device configuration allows for the independent identification and modeling of percolation as a function of guest concentration. Moreover, in standard unipolar devices where charges can move across all components (host-to-host, guest-to-guest, host-to-guest and guest-to-host), we found that charge transport predominantly occurs <i>through</i> guest-to-guest percolation. We define the critical concentration threshold for percolation and demonstrate its significant dependence on the trap depth of guest molecules. Our study establishes a foundational understanding of collective charge dynamics, particularly emphasizing the role of percolation in organic host-guest systems.