Evaluation of Alternate Materials for Organic/Inorganic Tunneling Diodes for Efficient, Water-Free and Flexible Organic Tandem Solar Cells
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Date
2015-12
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The Ohio State University
Abstract
Multi-junction Solar Cells are fabricated with multiple PN junctions in order to absorb light more efficiently than traditional solar cells. However, by stacking each of the multiple PN junctions in the solar cells to absorb different portions of the sun’s spectrum, parasitic resistances are formed between each stacked PN junction due to polarity mismatches that reduces collection efficiencies. The problem that this research addresses is the need to develop flexible and robust tunneling junctions, which are a critical element in fabricating these flexible solar cells. The purpose of the current research is to evaluate staggered junction candidates for the metal oxide and organic semiconductor in the fabrication of polymer tunneling diodes. This research study was prompted by prior research by Prof. Berger’s group at Ohio State that demonstrated the feasibility to fabricate polymer based tunnel diodes using a thin metal oxide (TiO2) and a conjugated polymer, Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) that exhibited negative differential resistance (NDR) function at room temperature. Although these seminal plastic NDR diodes are targeted for low power digital electronics, it is envisioned that modifications by materials replacements have the potential to form flexible tunneling junctions for multi-junction solar cells and offer higher flexibility and lower costs than their inorganic alternatives, such as silicon. The focus of this current research work is to target this new application for highly transparent and low-resistance organic-based flexible tunneling diodes as a replacement for existing alternatives, which have lifetime issues related to metallic shorts and the inclusion of water-based materials. This work will streamline the
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fabrication process of the tunneling diodes convolved with solar cell fabrication above and below it. Preliminary results for this research show that diodes substituting TiO2 with MoO3 and MEH-PPV with Copper Phthalocyanine (CuPc), do not indicate Zener tunneling behavior. This means that these materials, while excellent candidates, require further study to be utilized for this application. The potential benefits of this work are more efficient tunnel junctions for flexible, organic multi-junction solar cells that offer higher flexibility, manufacturability, lower costs, water-free, low-resistance with greater portability than their inorganic alternatives. At a deposition height of 43mm, which is measured from the top of the chamber.
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Keywords
Tunneling Diode, Tandem, Solar, Organic