A 260？nm layer of organic bulk heterojunction blend of the polymer poly(3-hexylthiophene) (P3HT) and the fullerene [6,6]-phenyl C61-butyric (PCBM) was spin-coated in between aluminum and gold electrodes, respectively, on top of a laser inscribed azo polymer surface-relief diffraction grating. Angle-dependent surface plasmons (SPs) with a large band gap were observed in the normalized photocurrent by the P3HT-PCBM layer as a function of wavelength. The SP-induced photocurrents were also investigated as a function of the grating depth and spacing. 1. Introduction In the recent years, research on photovoltaic cells has spread beyond inorganic materials, especially in the advent of thin-film solar cells. Despite their low efficiency, organic solar cells have generated much research interest, mainly because of their ease of fabrication and processability [1–3]. The bulk heterojunction blend of the polymer poly(3-hexylthiophene) and the fullerene [6,6]-phenyl C61-butyric (P3HT-PCBM) is one of the most promising organic solar cell materials [4]. The P3HT is a conducting polymer that produces the photovoltaic effect via the excitation of the -orbit electrons, while the PCBM possesses a high hole mobility and acts as an acceptor. The P3HT is the hole conductor while the PCBM is the electron conductor [5]. Many papers have reported on how the photovoltaic properties of the P3HT-PCBM blend can be enhanced depending on the sample preparation conditions, such as thermal annealing [6, 7] and its concentration in solvent [8]. Other papers have also reported on how to further increase the efficiency and the challenges present with these bulk heterojunction cells [9–11]. Since thin-film solar cells have a thickness in the order of a micron or less, wavelength-sized structures can be used to trap light inside the photovoltaic film. The integration of diffraction gratings either in the substrate or in the solar cell material itself has been successfully studied in thin-film silicon cells [12, 13] and in organic solar cells [14, 15]. Surface plasmons (SPs), which are electromagnetic waves that propagate at the interface between a metal and a dielectric, have also proved to increase light entrapment and absorption in both silicon [16–18] and organic thin-film solar cells [19–22]. Surface plasmons can be excited by matching the momentum and energy of the incident light beam to that of the plasmon along the direction of propagation. This can be done using a corrugated relief grating as well as metallic nanoparticles. In the absence of a band gap, the surface plasmon wave
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