| Organic materials are synthetically numerous, mechanically flexible, light weight, processable at low temperature, and chromatically diverse. For those organic materials with favorable electronic structure and classified as semiconductors, these unique characteristics can be readily leveraged for functional electronic and optoelectronic applications. This thesis examines the wide scope of realizable device structures that are enabled by the processability and adaptability of these materials, focusing on photodiode devices designed for both the detection and the harvesting of optical energy.;In the first part, two device structures are explored for their ability to output a photocurrent gain. Photocurrent gain, in which one incident photon gives rise to a multiple number of secondary photo-electrons cycled through an external circuit, is an important device property for applications that require the detection of low light signals and also those that require a more simplified electronic circuit. The field-effect transistor device structure is first studied, and it is found that although this structure can give rise to a small photocurrent gain up to G = 2, there are a number of trade-offs that may limit functionality. Next, a new multilayer organic photodiode structure is designed and studied that uses a carrier-selective confinement material to produce an extraordinarily efficient photoconductive gain mechanism, achieving G = 100--200 across the entire visible spectrum under a low applied bias (V = -3 V). The nature of the gain mechanism leads to relatively high bandwidth (f3dB = 1 kHz), and optimized devices are found to produce record gain-bandwidth product, up to GBP = 105, among organic photodetectors operating above imaging-compatible bandwidth (> 60 Hz).;In the second part, the focus is shifted to organic photovoltaic devices. First, a new device structure is proposed that utilizes a photoluminescent external absorption antenna in order to down-convert part of the incident solar spectrum into an emission spectrum that is more efficiently absorbed by the solar cell. The application of a down-conversion structure to a few typical organic solar cells is computationally studied and it is found that the concept can enhance organic solar cell performance. Depending on the material and device structure, the enhancement to total solar cell absorption efficiency can reach 27%.;Finally, as the ultimate advantage of organic solar cells may lie in their processability and commercial scalability, the final topic studied focuses on the processing of these cells by spray deposition. Spray deposition may enable low cost manufacture, however it inherently produces rough and non-ideal film morphology. Here it is proposed and confirmed that the addition of alkane diluents to a solution of polymer semiconductor and solvent can improve the uniformity of spray droplet deposition patterns. Furthermore, it is shown that the improvement in uniformity can significantly enhance solar cell power conversion efficiency (PCE) by up to 40%, reaching performance similar to that achieved by the highly uniform spin coating method. |
