| Description |
Semiconductors are an integral part of modern technology and are found in almost every aspect of our daily lives. The widespread application of semiconductor technology is based on the use of materials that exhibit properties tailored to specific purposes. Semiconductors that are strong absorbers of visible light are often used in photovoltaic and photodetector devices while narrow bandgap materials have found utility in thermoelectric applications. Determination of suitable applications for semiconductors is guided by intrinsic properties such as electronic structure, thermal conductivity, and electrical conductivity. Within the realm of electrical conductivity, carrier type is an important feature that must be considered in semiconductors. Most materials possess either holes or electrons as their majority carrier type and are described as p- or n-type, respectively. In this work, we report on the development of new n-type semiconductor materials using chalcogenide substitution. Substitution of selenium in bismuth sulfide (Bi2S3) by formation of solid solutions is shown to improve the electrical conductivity. Introduction of selenium into the Bi2S3 lattice results in a decrease in optical bandgap while carrier concentration and electrical conductivity are enhanced. In perylene diimide (PDI) molecules, the carbonyl moiety is substituted for a thiocarbonyl group that allows the control of optoelectronic properties. Through systematic thionation of the PDI molecule, we elucidated the effects that thionation have on their optoelectronic properties while simultaneously determining the physical iv implications of dimerizing these molecules. From ultraviolet spectroscopy measurements, we determined that the narrowing of the optical bandgap stems from lowering the lowest unoccupied molecular orbital as the degree of thionation is increased. Additionally, the dimerized PDIs overcome issues associated with intermolecular aggregation. The designed molecules demonstrate potential for use in bulk heterojunction devices based on proper orbital energy alignment and morphological interaction between donor and acceptor species. Finally, the synthesis and characterization of a novel inorganic-organic p-n heterojunction is reported. Sonochemical grafting of PDI onto hydrothermally prepared tin (II) sulfide (SnS) nanowires affords a heterojunction with controllable donor-acceptor ratios. Effective charge transfer from SnS to PDI is demonstrated where we observe an enhanced efficiency with which electrons are transferred from p-type SnS to n-type PDI. |
