No Access Submitted: 08 December 2014 Accepted: 20 January 2015 Published Online: 03 February 2015
Journal of Applied Physics 117, 055501 (2015); https://doi.org/10.1063/1.4907213
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Bulk Heterojunction (BHJ) organic photovoltaic devices performances depend on the relative organization and physical properties of the electron-donor and -acceptor materials. In this paper, BHJs of poly(3-hexyl-thiophene) (P3HT) associated with an electron acceptor material, 1-(3-methoxycarbonyl)-propyl-1-phenyl[6,6]C6 (PCBM) or [Ni(4dodpedt)2], are studied in terms of morphology, ordering, and electrical properties. First, comparison between the two BHJs performed by Atomic Force Microscopy (AFM) and Raman characterizations shows that P3HT structuration is improved by blending with [Ni(4dodpedt)2]. Then, the relationship between charges trapping, electrical properties, and film morphology is investigated using conductive AFM and Kelvin Force Microscopy. Measurements in dark condition and under solar cell simulator provide complementary information on electrical phenomena in these organic nanostructures. Finally, time dependent measurement highlights the influence of charges stacking on conduction. Specifically, we demonstrate that charge accumulation initiated by illumination remains valid after switching off the light, and induces the modification in current versus voltage characteristic of P3HT: PCBM blend. Finally, we observe a current increasing which can be attributed to the energy barrier decreasing due to charges trapping in PCBM.
This work was partly supported by the French RENATECH network and by the INSIS Institute of CNRS. The financial support by the Mexican Consejo Nacional de Ciencia y Tecnológica (CONACYT) was acknowledged.
From technical point of view, the authors thank Bruker for the access to ICON customized for AFM measurement under illumination, and Corinne Routaboul for her technical help during Raman spectroscopy measurements.

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