• Dastoor, Paul
• Feron, Krishna
• Zhou, Xiaojing
• Belcher, Warwick
• Al-Mudhaffer, Mohammed
• Thameel, Mahir

Abstract

Electronic energy level engineering, with the aim to improve the power conversion efficiency in ternary organic solar cells, is a complex problem since multiple charge transfer steps and exciton dissociation driving forces must be considered. Here we examine exciton dissociation in the ternary system poly(3-hexylthiophene): [6,6]-phenyl-C61-butyric acid methyl ester:2,4-bis[4-(N,N-diisobutylamino)-2,6- dihydroxyphenyl] squaraine (P3HT:PCBM:DIBSq). Even though the energy level diagram suggests that exciton dissocation at the P3HT:DIBSq interface should be efficient, electron paramagnetic resonance and external quantum efficiency measurements of planar devices show that this interface is not capable of dissociating excitons. Efficient exciton dissociation is still realised via energy transfer, which transports excitons from the P3HT:DIBSq interface to the DIBSq:PCBM interface, where the excitons can dissociate efficiently. This work demonstrates that energy level diagrams alone cannot be relied upon to predict the exciton dissociation capability of an organic semiconductor interface and that energy transfer relaxes the energy level constraints for optimised multi-component organic solar cells.

Topics

• impedance spectroscopy
• semiconductor
• ester
• power conversion efficiency