Single-layered photovoltaics based on cyano-substituted pyrazoloquinoline chromophores

Abstract

The efficiency of a single-layered photovoltaic (PV) cell was increased by up to 44% by using cyano-substituted pyrazoloquinoline chromophores. The role of the incorporated chromophore in changing the effective exciton radius formed by Coulombic chromophore–polymer interactions was analyzed using density functional theory (DFT) quantum chemical simulations. Both the ground-state dipole moments of chromophore, as well as their electrostatic interactions with the conjugated conducting polymer chains, are shown to play an important role. In particular, incorporation of the highly polarised cyano group leads to enhancement of the ground-state dipole moments and enables an open-circuit voltage up to 1.107 V, an enhancement of at least 40% compared to pyrazoloquinoline without cyano groups. At the same time, the exciton length determined by chromophore–matrix interactions and polaronic effects demonstrate a stronger correlation with the observed PV efficiencies.

Keywords:

• photovoltaic cell
• chromophore
• exciton radius
• cyano substitution
• dipole moment

Acknowledgement

This work was supported by grant 66/N/Singapore/2007/0.