Highly Efficient Hybrid Solar Cells Based on an Octithiophene–GaAs Heterojunction

Authors

  • J. Ackermann,

    1. Laboratoire des Matériaux Moléculaires et des Biomatériaux, GCOM2 CNRS UMR 6114, Faculté des Sciences de Luminy, Case 901, 163 avenue de Luminy, F-13288 Marseille Cedex 09, France
    2. Present address: Centre de Recherche de la Matière Condensée et des Nanosciences (CRMC-N), UPR 7251, Université de la Méditerranée (Aix-Marseille II), Campus de Luminy, 163 Av. de Luminy Case 913, F-13288 Marseille Cedex 09, France.
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  • C. Videlot,

    1. Laboratoire des Matériaux Moléculaires et des Biomatériaux, GCOM2 CNRS UMR 6114, Faculté des Sciences de Luminy, Case 901, 163 avenue de Luminy, F-13288 Marseille Cedex 09, France
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  • A. El Kassmi,

    1. Laboratoire des Matériaux Moléculaires et des Biomatériaux, GCOM2 CNRS UMR 6114, Faculté des Sciences de Luminy, Case 901, 163 avenue de Luminy, F-13288 Marseille Cedex 09, France
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  • R. Guglielmetti,

    1. Laboratoire de Chimie et Matériaux Organiques-Modélisation, GCOM2 CNRS UMR 6114, Faculté des Sciences de Luminy, Case 901, 163 avenue de Luminy, F-13288 Marseille Cedex 09, France
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  • F. Fages

    1. Laboratoire des Matériaux Moléculaires et des Biomatériaux, GCOM2 CNRS UMR 6114, Faculté des Sciences de Luminy, Case 901, 163 avenue de Luminy, F-13288 Marseille Cedex 09, France
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  • We are grateful to P. Raynal for helpful technical assistance with the synthesis of 8T, Dr. H. Oughaddou for his support in J–V and EQE measurements, and CRMC-N laboratory at the Faculté des Sciences de Luminy in Marseille, France, for stimulating discussions and access to their AFM instruments.

Abstract

We report a new type of hybrid heterojunction solar cell based on rod-like octithiophene (8T) as the organic p-type semiconductor and GaAs(111) as the inorganic n-type semiconductor. By using a semitransparent gold layer as the front contact deposited onto the 8T films, solar-energy conversion efficiencies of up to 4.2 % could be obtained. The reduction in the contact resistance at the Au/8T interface induced by iodine doping is found to be a very crucial factor for the high efficiency. Furthermore, we demonstrate that hybrid solar cells can be successfully used to investigate the photovoltaic properties of organic semiconductors in detail. By means of external quantum efficiency (EQE) measurements, the influence of film morphology on the photocurrent collection length in 8T films is studied. The results show that, in hybrid solar cells using highly ordered microcrystalline 8T films, an active contribution of the organic-layer semiconductor to the total photocurrent exists. A very large photocurrent collection length of up to 100 nm has been estimated from EQE measurements, indicating that exciton diffusion is very efficient in microcrystalline 8T. On the other hand, the use of nanocrystalline 8T leads to high photocurrent losses in the organic part of the hybrid solar cell. The strong influence of the film morphology on the photocurrent collection in 8T is attributed to a reduction in the exciton diffusion length due to a high trap density in nanocrystalline 8T films. Thus, our results reveal the importance of high crystalline order for obtaining efficient photocurrent collection in 8T films.

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