How visual representations affect undergraduate students’ use and understanding of engineering concepts during problem solving

[摘要] In this two-part thesis, I address gaps in the surface science of semiconductor materials for photovoltaics and discipline-based education research literature.Surface Science of Semiconductor Materials for PhotovoltaicsWith the rise of global energy consumption, it is important to find low-cost, renewable sources of energy. Photovoltaic devices (i.e., solar cells) are one such source of energy, converting solar energy into electricity. However, their levelized cost of electricity (i.e., $/MW*h) is currently too high to compete with traditional electricity sources. One way to lower this cost is to increase the solar cell’s power conversion efficiency, which is often limited by defects throughout the device. While defect behavior is well-studied in the community, the techniques used are not chemically sensitive, so experiments must be combined with computation to identify defects. Understanding the chemical identity of defects is particularly important for improving the efficiency of solar cells that use CuInSe2 (CIS) and Cu(In,Ga)Se2 (CIGS) as the absorber layer, which are inexpensive but limited due to a variety of defects. Understanding which elements are involved in charge capture and recombination would contribute to the literature by providing a fundamental understanding of defects in materials important to the photovoltaic industry. In this study, I studied charge capture on defects within the CIS side of the CdS/CIS interface using photo-modulated x-ray photoelectron spectroscopy (XPS) to observe changes in surface charging under illumination. My work provides some of the first experimentally verified evidence of electron capture on Cd donor atoms within CIS thin films. Others in the field can use my work to investigate the effect of Ga- or grain boundary-based defects in CIGS thin films or on other materials such as perovskites or CuZnSnS4 whose defect behavior under illumination is also relatively unexplored using chemically-sensitive techniques.Discipline-Based Education ResearchWhether sketching an idea on the back of a napkin, drawing schematics on a whiteboard, or using computational tools to understand unobservable phenomena, engineers need to be able to solve problems and communicate their knowledge with a variety of visual representations. Research into how students use visual representations has so far focused on questions such as “will a picture or a graph improve students’ problem-solving ability” rather than “what about the graphical representation causes differences in students’ problem-solving ability?” To address this gap, I conducted a sequential exploratory mixed methods study to characterize and test the interplay between students’ level of conceptual knowledge, how concepts are encoded within representations, and how students use concepts during problem solving both within and across two engineering disciplines. The results of my work are 1) three types of features in visual representations that affect student’ problem solving and 2) a classroom intervention based on the findings from the think-aloud interviews to test the generalizability of my first finding. My work contributes to the community by applying a well-known theoretical framework that describes how people process visual information to novel contexts and developing deeper insights into the novice-expert transition. Additionally, my work provides the community with a data-driven theory to analyze how specific types of visual representations might be inhibiting engineering students’ ability to learn concepts and use them effectively when solving problems.

[关键词] engineering education