Deciphering the microscopic phenomenon behind contact resistances in interlayer functionalized electrodes and organic semiconductors

Interlayers are known to enhance the performance of organic devices by reducing contact resistance, however, the details of the mechanism are uncertain. Models have correlated properties of interlayers to their extent of reduction of contact resistance, but a universal parameter correlating the microscopic phenomenon to device characteristics is yet to be established. Here, we demonstrate that the energy-level modulation at the interface of interlayer functionalized electrode and organic semiconductor, combined with the charge transfer integral between them, determines the extent of the reduction of contact resistance. Moreover, the rate of charge transfer calculated from these quantities is demonstrated to be a universal parameter predicting the characteristics of devices with functionalized electrodes, regardless of the nature of the semiconductor (p- or n-type). These observations explain the mechanism of interlayers and provide a computational model capable of selecting interlayers leading to high-performing devices.