Fabrication and characterization of fullerene-based solar cells containing phthalocyanine and naphthalocyanine dimers

doi:10.1016/j.synthmet.2013.06.011

Synthetic Metals

Volume 177, 1 August 2013, Pages 48-51

https://doi.org/10.1016/j.synthmet.2013.06.011 Get rights and content

Highlights

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Fullerene-based GaPc and GaNc dimer solar cells were fabricated.
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The solar cells with inverted structures have high stability in the air.
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The solar cells showed a wide optical absorption ranging from 320 nm to 800 nm.
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A carrier transport mechanism was discussed based on energy level diagram.

Abstract

Fullerene-based solar cells with normal and inverted structures containing phthalocyanine and naphthalocyanine dimers were fabricated by vacuum evaporation. Power conversion efficiencies were measured under simulated sunlight conditions. Fabricated devices exhibited high stability in air and a wide optical absorption from 320 to 800 nm. A carrier transport mechanism is proposed based on the energy level diagram.

Introduction

Organic thin film solar cells are a promising low cost renewable energy source. They can be fabricated on large area, light weight flexible substrates at low temperature, using coating and printing methods. Organic solar cells are attractive as ‘next generation’ solar cells. Metal phthalocyanines (MPc) exhibit photovoltaic activity, heat-resistance, solar and chemical stability, and high absorption across the visible spectrum. They are used as catalysts in oxidation, fuel cells and solar cells. An efficiency of ∼5% has been achieved for organic solar cells with a normal structure. That of ∼0.3% has been achieved for inverted structure solar cells, by employing molecules such as copper phthalocyanine and fullerenes [1], [2], [3]. High photocurrents have been reported when two adjacent phthalocyanines with amino and hydroxyl substituents were arranged with a hydrogen bridging substituent [4]. Few solar cell structures incorporating phthalocyanine dimers have been reported [5].

Although easily fabricated, organic solar cells are not stable, possibly because of photo-induced diffusion of O₂ into C₆₀, or the reaction of the Al electrode with oxygen and water. Solar cells incorporating non-corrosive Au electrodes have recently been developed to overcome this. Such solar cells have an inverted device structure compared with the normal structure, in which photo-generated electrons flow through an external circuit from the transparent working electrode to Au electrode [6], [7], [8].

In this study, phthalocyanine dimer solar cells with normal and inverted structures were fabricated and characterized. μ-Oxo-bridged gallium phthalocyanine (GaPc) dimer, aluminum phthalocyanine (AlPc) dimer, gallium-titanium phthalocyanine (Ga-TiPc) dimer and gallium naphthalocyanine (GaNc) dimer were used as the p-type semiconductors. Fullerene (C₆₀) and [6,6]-phenyl-C₆₁ butyric acid methyl ester (PCBM), a fullerene derivative, were used as the n-type semiconductors.

Section snippets

Experimental

Solar cells with normal structures were fabricated by spin-coating thin layers of polyethylenedioxythiophene doped with polystyrenesulfonic acid (PEDOT:PSS, Sigma–Aldrich Co.) on pre-cleaned indium tin oxide (ITO) glass plates (Geomatec Co., Ltd., ∼10 Ω/□) at 2000 rpm. PEDOT:PSS acts as an electron blocking layer for hole transport. After annealing at 100 °C for 20 min in a N₂ atmosphere, the GaPc, AlPc, Ga-TiPc or GaNc dimer (Orient Chemical Industries, Co. Ltd.) layer was vacuum evaporated on the

Results and discussion

J–V characteristics measured from the solar cells are summarized in Table 1. The device structures exhibited characteristic curves for the open-circuit voltage (V_oc) and short-circuit current density (J_sc). The GaPc dimer/C₆₀ device exhibited the best performance for a normal structure, with power conversion efficiency (η) of 0.035%, fill factor (FF) of 0.30, V_oc of 0.18 V and J_sc of 0.64 mA/cm². The PCBM/GaPc dimer device exhibited the best performance for an inverted structure, with η of

Conclusions

Phthalocyanine and naphthalocyanine dimer containing solar cells with normal and inverted structures were fabricated and characterized. The GaPc dimer/PCBM inverted device exhibited η of 0.14%, FF of 0.25, V_oc of 0.51 V and J_sc of 1.12 mA/cm². The solar cell retained its function following 2 months’ exposure in air. A carrier transport mechanism was proposed based on the energy level diagram.

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The synthesis of novel directly conjugated zinc(II) phthalocyanine via palladium-catalyzed Suzuki–Miyaura cross-coupling reaction and its quaternized water-soluble derivative: Investigation of photophysical and photochemical properties
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Fabrication and characterization of fullerene-based solar cells containing phthalocyanine and naphthalocyanine dimers

Highlights

Abstract

Introduction

Section snippets

Experimental

Results and discussion

Conclusions

Dyes and Pigments

Chemical Physics Letters

Solar Energy Materials and Solar Cells

Thin Solid Films

Journal of Physics and Chemistry of Solids

Acta Physico-Chimica Sinica

Journal of Applied Physics