Discontinuous pn-heterojunction for organic thin film transistors

Utilization of discontinuous pn-oragnic heterojunction is introduced as a versatile method to improve charge transport in organic thin film transistors (OTFTs). The method is demonstrated by depositing n-type dioctyl perylene tetracarboxylic diimide (PTCDI-C₈) discontinuously onto base p-type pentacene OTFTs. A more pronounced impact of the discontinuous upper layer is obtained on the transistor performances when thinner base layers are employed; a >100-fold enhancement in hole mobility and a >20 V shift in threshold voltage are achieved after applying PTCDI-C₈ discontinuously onto 2 nm thick pentacene thin films. Local surface potential measurements (Kelvin-probe force microscopy) and temperature-dependent transport measurements (77-300 K) reveal that the interfacial dipole formed at the pn-heterostructures effectively dopes the base pentacene films p-type and leads to a reduction in transport activation energy.