Browse Prior Art Database

New Class of Organic Photoconducting and Photovoltaic Materials

IP.com Disclosure Number: IPCOM000087811D
Original Publication Date: 1977-Mar-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 3 page(s) / 28K

Publishing Venue

IBM

Related People

Braccini, RB: AUTHOR [+4]

Abstract

This article describes a new class of materials for photovoltaic devices. Their high photoconductivities also make them applicable to high speed electrophotographic systems, such as copying machines.

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New Class of Organic Photoconducting and Photovoltaic Materials

This article describes a new class of materials for photovoltaic devices. Their high photoconductivities also make them applicable to high speed electrophotographic systems, such as copying machines.

Organic Schottky barrier solar cells based on the organic dye squarylium modified by methyl- and hydroxy-substitution have been developed previously. More recently, power conversion efficiencies of up to 0.05% in hydroxy squarylium thin film Schottky barrier devices have been attained. Treating such films with electron acceptors such as bromine (or other halogens) has led to transient power conversion efficiencies of up to 0.16%. However, such cells are unstable and, with time, decay to efficiencies typical of undoped films. Probably, the halogen is strongly absorbed into the surface layers of these films, where they oxidize some of the dye molecules, creating a mixed valency dye system having higher dark conductivity and photoconductivity than the unreacted film. However, the reaction with halogen slowly reverses as it comes to equilibrium, causing the cell resistance to return to its previous (undoped) value. An attempt is now being made to stabilize this process by studying the reaction with halogen and other acceptors.

A most important property of squarylium dyes for photovoltaic applications is their very high absorption coefficients in the visible spectrum. However, like most organic insulators, once excited, these systems return rapidly to their ground states or produce excitons with long enough lifetime to propagate through the crystal before being quenched by impurities, defects, or by the surface. Thus, the free carrier photogeneration efficiencies tend to be very low and, even where moderately high, the low hole and electron mobilities, presence of traps, defects, etc., make these compounds poor photoconducting and photo-voltaic materials despite their low preparation and processing costs.

If high optical absorption could be combined with high carrier photogeneration efficiency in organic systems, much more efficient organic photovoltaic Schottky barrier devices could be produced. It is proposed that salts of the type (Dye./+/)(TCNQ/-/) and (Dye/+/)(TCNQ/-/) (TCNQ/degree/) combine these two important features, provided there exists strong coupling between the dye molecular arrays a...