Visualisation of charge-transfer excitations in donor–acceptor molecules using the particle–hole map: a case study

ABSTRACT

Charge-transfer (CT) excitations are essential for photovoltaic phenomena in organic solar cells. Owing to the complexity of molecular geometries and orbital coupling, a detailed analysis and spatial visualisation of CT processes can be challenging. In this paper, a new detail-oriented visualisation scheme, the particle–hole map (PHM), is applied and explained for the purpose of spatial analysis of excitations in organic molecules. The PHM can be obtained from the output of a time-dependent density-functional theory calculation with negligible additional computational cost, and provides a useful physical picture for understanding the origins and destinations of electrons and holes during an excitation process. As an example, we consider intramolecular CT excitations in Diketopyrrolopyrrole-based molecules, and relate our findings to experimental results.

GRAPHICAL ABSTRACT

Keywords:

• Charge-transfer excitations
• organic photovoltaics
• particle–hole map
• time-dependent density-functional theory

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Y. Li and C.A.U. were supported by the National Science Foundation [grant number DMR-1005651], [grant number DMR-1408904]. D.M. and S.G. acknowledge support from the University of Missouri Research Board.