Organic Solar Cells

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Organic Solar Cells Based on a Solution Phase Near-IR Absorbing Soluble Phthalocyanines Tech ID: UA11-105 Invention: This invention is a solution-processed planar heterojunction (PHJ) organic photovoltaic (OPV) device based on a soluble titanyl phthalocyanine (TiOPc) derivative as the donor with photo activity extended up to 1 micron in the near-IR region of the solar spectrum, without significantly affecting the open-circuit photopotential (Voc). TiOPc is a metallated phthalocyanine bearing a Ti=O bond orthogonal to the molecular plane. The presence of the dipole in the axial direction leads to a face-to-face arrangement of the molecules which maximizes the p-orbital overlap. Depending on the degree of p -orbital overlap in the condensed phase, TiOPc can exist in polymorphs such as Phase-I (or b-phase) and Phase-II (a-phase) that are active in the near-IR. A direct consequence of such an arrangement is high photoconductivity, third order non-linear susceptibility, and near-IR absorptivity that makes this material and invention a promising candidate for advanced technologies such as OPV and optical limiting devices. Background: The solar cells in this invention convert sunlight in the near-IR region of the solar spectrum to electricity, and they are constructed from soluble small molecule, rather than polymer, donor materials. The efficiency of organic solar cells is limited by the number of photons absorbed within the active layer thickness, which is confined to the visible region for most chromophores while 50% of the AM1.5G solar irradiance is incident in the near-IR region. If thin-film absorptivities can be extended to the near-IR with no significant loss in the Voc, a significant improvement in power conversion efficiencies (h) can be anticipated. Solution-processed small-molecules as donors have been a subject of several recent investigations due to their facile synthesis, purification, tunability, and inherent monodispersity. Unlike vacuum deposition, which is still the predominant mode of film-deposition, solution-processable chromophores can deposit thin-films over large areas using techniques such as reel-to-reel wet coating, ink-jet printing, and spin-coating. Status: The best devices constructed so far from organic materials are those based on poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM) systems, which are transparent in the near-IR region. More recently, low band gap polymers in combination with PC70BM have exceeded 8% power conversion efficiencies, which still do not have appreciable absorbance above 750-800 nm.