Organic Photovoltaic Devices: Atmospheric Fabrication and Characterization

Abstract

Organic electronics show promise as a future alternative to crystalline inorganic semiconductors in a variety of applications, with advantages in flexibility, and fabrication cost. Organic photovoltaic devices are one such application with a growing demand for clean energy, solar energy has the possibility to fill a large portion of the demand. This thesis focuses on the fabrication and testing of organic photovoltaic devices in ambient conditions, from initial device fabrication to manipulation of device structure to invert the flow of electrons, ending with a small look at the change in device function while exposed to simulated solar illumination.

The theory of photovoltaic devices and properties of organic electronic materials are the basis of device design. Considering the competing factors of charge transport, recombination and absorption, devises can be designed to operate within a reasonable efficiency. To improve device function degradation and device limiting factors must be considered and rectified.

Device fabrication utilized two basic techniques spin coating for all organic materials and physical vapor deposition for inorganic materials. A single set of acceptor donor absorption pair were utilized, with three different buffer materials, and two different metals for contacts. These materials were combined in a simple planar bulk heterojunction architecture. Standard device testing methods were employed to ensure valid comparison with reported results.

Initial devices failed due to a variety of factors, from shorts in the devices caused by insufficient cleaning of substrates to destruction of devices due to testing apparatus. Rectifying these problems resulted in devices having power conversion efficiencies as high as 3.23\% using a material that is not expected to exceed 5\%. Manipulation of device structure by substitution of materials confirmed device design principles, including the inversion of device current flow by changing the buffer materials. Changes in device function due to exposure to solar illumination over a short period were investigated, yielding mixed results dependent on the initial state of the device.