Carrier concentration increase in OFETs with interface barrier and Fermi level difference

Abstract

It was found that interface barrier is beneficial to form accumulation heterojunction in organic semiconductor. A new theoretical model has been established with combined effect of interface barrier and EF level difference between p-type and n-type materials. The organic pn-heterojunction has been put forward in OFETs for further research, 2 nm perylene diimide (PDI) and its derivatives (PDI-1)/(PDI-2) are used as discontinuous films to modify pentacene OFETs. The accumulative effect will be further enhanced under the joint effect of interface barrier and greater EF level difference. With the downgrading of LUMO level for n-type materials, the hole concentration in pentacene was increased by 12.3 times, 36.9 times and 107.4 times respectively, and VT shifted from −6.90 V to −2.67 V, 0.64 V and 6.82 V, the OFETs performance have been optimized efficiently, and the devices can be converted from enhancement-mode to depletion-mode. The LUMO level of PDI-2 was pinned to the EF level of pentacene has been verified by employing the organic-organic interface energy level alignment (OOI ELA) theory. The dramatic increase of carrier concentration is theoretically revealed at both sides of pn-heterojunction.