Subgap Absorption in Organic Semiconductors

Organic semiconductors have found a broad range of application in areas such as light emission, photovoltaics, and optoelectronics. The active components in such devices are based on molecular and polymeric organic semiconductors, where the density of states is generally determined by the disordered nature of the molecular solid rather than energy bands. Inevitably, there exist states within the energy gap which may include tail states, deep traps caused by unavoidable impurities and defects, as well as intermolecular states due to (radiative) charge transfer states. In this Perspective, we first summarize methods to determine the absorption features due to the subgap states. We then explain how subgap states can be parametrized based upon the subgap spectral line shapes. We finally describe the role of subgap states in the performance metrics of organic semiconductor devices from a thermodynamic viewpoint.

Automated summary

Organic semiconductors have various applications in areas such as light emission, photovoltaics, and optoelectronics. The characteristics of these devices are determined by the disordered nature of the molecular solid rather than energy bands. However, there are subgap states within the energy gap that may affect the performance of organic semiconductor devices. This Perspective discusses methods to determine these subgap states and their impact on device performance.