Hybrid Organic/Inorganic Optoelectronics.

Abstract

Traditional inorganic semiconductors are the foundation of modern electronics. These materials are widely used in computing and optical devices (such as lasers, LEDs, cameras, etc.), but they are limited in functionality by their particular set of material properties. In particular, traditional crystalline inorganic semiconductors are not well suited for large area or flexible electronics applications. This limitation has driven the development of a new generation of thin-film semiconductor materials. Thin-film semiconductor materials are ideal for solar energy conversion because they have the potential for cost effective large area fabrication. Promising next generation photovoltaic devices have been demonstrated using organic photovoltaics (OPVs) and dye-sensitized solar cells (DSSCs). OPVs are a promising technology because they are inexpensive, strong absorbers. However, it is challenging to produce efficient OPVs due to the excitonic nature and poor charge transport characteristic of these materials. DSSCs are hybrid devices that combine the strong absorption of organic semiconductors with the good charge transport of inorganic metal-oxide semiconductors. Devices based on thin-film, low mobility, excitonic materials are governed by fundamentally different physical processes than traditional inorganic devices. In this thesis, we develop physical models to analyze the performance of devices based on organic/organic and hybrid organic/inorganic heterojunctions (HJs). These models are based on interface dynamics at the HJ and are used to identify the physical processes that limit device performance. Specifically, we extend the interface model to understand: 1) reciprocal carrier collection in OPVs, 2) photoconductivity in OPVs, 3) the adaptation of traditional depletion models to thin-film devices, and 4) space-charge effects in hybrid devices. To model hybrid devices, we introduce a theory that bridges the gap between traditional semiconductor theory and models developed to explain thin-film excitonic systems. Once the important physical processes are understood, we can proceed to design optimized devices. In the last section we consider the application of organic and hybrid devices for flexible or non-planar devices. Here, we develop technologies to enable the fabrication of high-performance devices and high-density circuits on flexible and non-planar substrates. We then demonstrate an integrated passive pixel photodetector array and discuss the extension to a high-performance hybrid sensor array.