Author ORCID Identifier
Year of Publication
Doctor of Philosophy (PhD)
Arts and Sciences
Dr. Kenneth R. Graham
In recent years, organic-inorganic metal halide perovskites (HP) have garnered tremendous attention in photovoltaic research. This attention is attributed to their low cost and excellent optoelectronic properties, including large absorption coefficients, tunable bandgaps, long charge-carrier diffusion lengths, and low densities of deep trap states. Inverted p-i-n architecture perovskite solar cells (PSCs) are of intense interest and are generally regarded as more amenable to low-temperature solution processing. Nevertheless, the development of inverted PSCs is lagging the conventional architecture devices. Imperfect energy level alignments and charge carrier recombination, especially at the interface between perovskite and electron transport layers (ETLs), are two main factors suppressing the power conversion in inverted PSCs. More and more efforts are focused on manipulating the interface to improve PV devices. Organic semiconductors (OSCs), including π-conjugated polymers and small molecules, display distinct advantages in terms of low-cost, lightweight, diverse structures, easy solution-processed manufacturing, as well as excellent mechanical flexibility. However, the performance of OSCs-based devices is lagging behind their inorganic counterparts, in part due to lower mobility and electrical conductivity. Molecular doping provides a route to significantly enhance electronic properties, and as a result, is progressively attracting more attention. My Ph.D. research interest is focused on the applications of photoelectron spectroscopies to the study of perovskite solar cells and organic semiconductor-based electronics. The first work carried out is how surface ligands impact interfacial energetics and charge carrier dynamics at methylammonium lead iodide (MAPbI3)/C60 interfaces. The frontier electronic energy levels at perovskite/C60 interfaces are directly probed by ultraviolet photoelectron spectroscopy (UPS) and low energy inverse photoelectron spectroscopy (IPES), providing evidence of interfacial energetic reconstruction caused by surface ligands with differing dipoles. Ultrafast absorption/reflectance spectroscopies and transient photovoltage/photocurrent are utilized in comprehensively picturing the charge dynamics in films and devices. The following work reports the doping mechanism in the photoactivated p-doping of hole-transporting material (HTM) to enhance hole extraction for perovskite/textured silicon tandem solar cells, making the device performance less sensitive to the variation of hole transport layer thickness. Lastly, several collaborative works on doping of organic semiconductors are discussed, with applications in organic solar cells and thermoelectrics.
Digital Object Identifier (DOI)
Liu, Tuo, "THE APPLICATION OF PHOTOELECTRON SPECTROSCOPIES IN ANALYZING THE IMPACT OF INTERFACIAL ENERGETICS ON PEROVSKITE SOLAR CELLS" (2023). Theses and Dissertations--Chemistry. 174.
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