Correlating Non-Geminate Recombination with Film Structure: A Comparison of Polythiophene: Fullerene Bilayer and Blend Films.
The morphology of the active layer in polymer:fullerene solar cells is a key parameter in determining their performance. In this study we monitor the charge carrier dynamics in bilayers of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) (fabricated by sequential spin coating and vacuum deposition) before and after thermal annealing, and compare these against conventional solution processed bulk heterojunction (BHJ) blend films. Transmission electron microscopy images, supported by field effect mobility data show that while not-annealed P3HT/PC61BM bilayers possess a sharp interface, intermixing proceeds upon annealing. Transient absorption studies indicate that the not-annealed bilayer yields fewer, but longer lived, charge carriers compared to the BHJ. Monte Carlo (MC) simulations further suggest that the difference in non-geminate recombination dynamics observed for the BHJ and bilayer films could be related to the confinement of charge carriers to the interface, with the lower dimensionality for the flat interface bilayer films relative to the intercalated donor-acceptor network BHJ films leading to lower recombination.
†Centre for Plastic Electronics, Department of Chemistry, Imperial College London, London SW7 2AZ, United Kingdom.
Safa
S
Shoaee
‡School of Chemistry and Biochemistry and Centre for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States.
Shafigh
S
Mehraeen
§Centre for Plastic Electronics, Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom.
John G
JG
Labram
‡School of Chemistry and Biochemistry and Centre for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States.
Jean-Luc
JL
Brédas
§Centre for Plastic Electronics, Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom.
Donal D C
DD
Bradley
‡School of Chemistry and Biochemistry and Centre for Organic Photonics and Electronics, Georgia Institute of Technology, Atlanta, Georgia 30332-0400, United States.
Veaceslav
V
Coropceanu
§Centre for Plastic Electronics, Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom.
Thomas D
TD
Anthopoulos
†Centre for Plastic Electronics, Department of Chemistry, Imperial College London, London SW7 2AZ, United Kingdom.
James R
JR
Durrant
charge generation; diffusion; nanomorphology; non-geminate recombination