Organic photosensitive devices comprising aryl squaraines and methods of making the same

Abstract

There is disclosed squaraine compounds of formula I:wherein each of Y1 and Y2 is independently chosen from an optionally substituted amino group and an optionally substituted aryl group. Also described are organic optoelectronic devices comprising a Donor-Acceptor heterojunction that is formed from one or more of the squaraine compounds. A method of making the disclosed device, which may include one or more sublimation step for depositing said squaraine compound, is also disclosed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to U.S. Provisional Application Nos. 61 / 441,153, filed on Feb. 9, 2011, and 61 / 479,231, filed on Apr. 26, 2011, both of which are incorporated herein by reference in their entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH[0002]The subject matter of this application was prepared with U.S. Government support under Contract No. DE-FG36-08GO18022 awarded by U.S. Department of Energy, Center for Energy Nanoscience, and Contract Nos. DE-SC0001013 and DE-SC0000957. The government has certain rights in the subject matter of this application.JOINT RESEARCH AGREEMENT[0003]The subject matter of this application was made by, on behalf of, and / or in connection with one or more of the following parties to a joint university-corporation research agreement: University of Michigan, University of Southern California, and Global Photonic Energy Corporation. The agreement was in effect on and before the date the claim...

AI Technical Summary

Benefits of technology

[0006]Photosensitive optoelectronic devices convert electromagnetic radiation into electricity. Solar cells, also called photovoltaic (PV) devices, are a type of photosensitive optoelectronic device that is specifically used to generate electrical power. PV devices, which may generate electrical energy from light sources other than sunlight, can be used to drive power consuming loads to provide, for example, lighting, heating, or to power electronic circuitry or devices such as calculators, radios, computers or remote monitoring or communications equipment. These power generation applications also often involve the charging of batteries or other energy storage devices so that operation may continue when direct illumination from the sun or other light sources is not available, or to balance the power output of the PV device with a specific application's requirements.

[0019]Electric fields or inhomogeneities at a contact may cause an exciton to quench rather than dissociate at the donor-acceptor interface, resulting in no net contribution to the current. Therefore, it is desirable to keep photogenerated excitons away from the contacts. This has the effect of limiting the diffusion of excitons to the region near the junction so that the associated electric field has an increased opportunity to separate charge carriers liberated by the dissociation of the excitons near the junction.

[0024]A significant property in organic semiconductors is carrier mobility. Mobility measures the ease with which a charge carrier can move through a conducting material in response to an electric field. In the context of organic photosensitive devices, a layer including a material that conducts preferentially by electrons due to a high electron mobility may be referred to as an electron transport layer, or ETL. A layer including a material that conducts preferentially by holes due to a high hole mobility may be referred to as a hole transport layer, or HTL. In one embodiment, an acceptor material is an ETL and a donor material is a HTL.

[0030]Through the use of an organometallic material in the photoactive region, the devices described herein may efficiently utilize triplet excitons. We have found that the singlet-triplet mixing may be so strong for some organometallic compounds, like squaraines, that the absorptions involve excitation from the singlet ground states directly to the triplet excited states, eliminating the losses associated with conversion from the singlet excited state to the triplet excited state. The longer lifetime and diffusion length of triplet excitons in comparison to singlet excitons may allow for the use of a thicker photoactive region, as the triplet excitons may diffuse a greater distance to reach the donor-acceptor heterojunction, without sacrificing device efficiency. Accordingly, there remains a need to further develop photosensitive devices comprising certain squaraines, including symmetric and asymmetric arylsquaraines.SUMMARY OF INVENTION

Problems solved by technology

A photodetector or photoconductor provides a signal or current to control detection circuitry, or the output of information from the detection circuitry but does not provide power to the circuitry, device or equipment.

However, efficient crystalline-based devices, especially of large surface area, are difficult and expensive to produce due to the problems inherent in producing large crystals without significant efficiency-degrading defects.

On the other hand, high efficiency amorphous silicon devices still suffer from problems with stability.

The maximum total power generated by a PV device is inherently incapable of exceeding the product, ISC×VOC.

Either of these outcomes is undesirable in a photosensitive optoelectronic device.

Such a process can be induced by the built-in electric field, but the efficiency at the electric fields typically found in organic devices (F˜106 V / cm) is low.

However, organic PV devices typically have relatively low external quantum efficiency (electromagnetic radiation to electricity conversion efficiency), being on the order of 1% or less.

In this process energy is lost which will result in a lower efficiency for the device.

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