Bulk-heterojunction based on blending of red and blue luminescent silicon nanocrystals and P3HT polymer.
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Bulk-heterojunction based on blending of red and blue luminescent silicon nanocrystals and P3HT polymer. Vladimir Švrček, Michio Kondo Novel Si Material Team, Research Center for Photovoltaics, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, Umezono 1-1-1, Tsukuba, 305-8568, JAPAN Corresponding e-mail: [email protected] ABSTRACT Blending of red and blue photoluminescent silicon nanocrystals (Si-ncs) with poly(3hexylthiophene (P3HT) conjugated polymer is demonstrated. The room temperature luminescent and ambient conditions stable Si-ncs prepared by electrochemical etching and laser ablation in water are used for the blend fabrication. Furthermore photo-electric properties in parallel configuration on platinum interdugitated contact are shown. Both types of Si-ncs results the bulk-heterojunction formation and photoconductivity is observed when the blends are irradiated AM1.5. The increase in photoconductivity is rather the same and ratio between photo- and darkconductivity is about 1.7. The nanocrystal oxidation during laser ablation fabrication process in water hinders the transport properties of the blend. INTRODUCTION Nowadays technologies and materials for solar cells are near their potential peak for converting photons to electricity. Therefore, new energy material development is timely and higly needed. Different innovative approaches are reported in literature for both cell and material design [1-4]. For instance, recent mean involving quantum dots have been propossed to control and increase the absorption as a function of the dot size [1]. Quantum dots and polymer based blends might provide low cost, and perspective solution for fabrication of low-cost hybrid solar cells [1, 3]. In particular silicon nanocrystals (Si-ncs) due to the quantum confinement effects, carrier multiplication, low-toxicity and photovoltaic technologies compatibility emerged to be very promising photovoltaic material [4-6]. Formation of bulk-heterojunction by blending of freestanding Si-ncs with conjugated polymers can be achieved [6], which results photosensitive blend fabrication. The blending of Si-ncs with different energy band gap, in principle, could allow so called a “tandem cell” fabrication. The multiple cells can be used with diferent gap controled by Si-ncs size, then each one converting a range of photons energies close to its bandgap. It has been shown that the electrochemical etching and laser ablation allow preparing the colloidal dispersible Si-ncs with well distinguished band gaps [7, 8]. On the other hand, it is expected that also new solar cell design might considerably improve the solar cell performance. It has been reported that the placing both negative and positive contact on the backside of the active layer has multiple advantages over the conventional sandwich structures [9]. An elimination of the front contact provides a potential to improve short circuit current and could lead to
interconnection in an easier and simpler way with a higher packing densi
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