Study on carrier excitation and accumulation effects in organic dual planar–bulk heterojunctions and their application in OFETs

Abstract

In this study, we propose an Organic Dual Planar–Bulk Heterojunctions (DP–BHJ) structure based on the conventional planar–bulk heterojunction. The key innovation lies in the introduction of a P:N blend layer (Pentacene:F16CuPc) between the organic p-type semiconductor (Pentacene) and n-type semiconductor (F16CuPc). This blend layer forms two planar heterojunctions with the adjacent semiconductors on both sides, while simultaneously constituting a bulk heterojunction itself. Such a configuration generates two vertically aligned built-in electric fields with the same orientation that superimpose, thereby enabling the heterojunction to exhibit enhanced carrier excitation and accumulation. As a result, the device demonstrates significantly increased on-state current and charge-carrier mobility. Conversely, under gate-off conditions, the high density of defect states inherent to the bulk heterojunction acts as a strong barrier to carrier transport, effectively suppressing the off-state current. This dual optimization of on-/off-state currents enhances overall device performance. When applied in organic field-effect transistors (OFETs), the DP–BHJ structure delivers a 2.4-fold improvement in mobility, a 2.9-fold increase in on-state current, and a 50% reduction in threshold voltage compared with conventional planar heterojunction OFETs. Furthermore, by inserting an ultrathin blend layer for interface engineering, the off-state current is greatly reduced, resulting in a markedly improved current on/off ratio.