Improving Photovoltaics with High Luminescence Efficiency Quantum Dot Layers

A solar cell relies on its ability to turn photons into current. Because short wavelength photons are typically absorbed near the top surface of a cell, the generated charge carriers recombine before being collected. But when a layer of quantum dots (nanoscale semiconductor particles) is placed on top of the cell, it absorbs short wavelength photons and emits them into the cell at longer wavelengths, which enables more efficient carrier collection. However, the resulting power conversion efficiency of the system depends critically on the quantum dot luminescence efficiency – the nature of this relationship was previously unknown. Our calculations suggest that a quantum dot layer must have high luminescence efficiency (at least 80%) to improve the current output of existing photovoltaic (PV) cells; otherwise, it may worsen the cell’s efficiency. Our quantum dot layer (using quantum dots with over 85% quantum yield) slightly reduced the efficiency of our PV cells. We observed a decrease in short circuit current of a commercial-grade cell from 0.1977 A to 0.1826 A, a 7.6% drop, suggesting that improved optical coupling from the quantum dot emission into the solar cell is needed. With better optical coupling, we predict current enhancements between ~6% and ~8% for a solar cell that already has an antireflection coating. Such improvements could have important commercial impacts if the coating could be deployed in a scalable fashion.

Catalyst: Architecture for Change and Social Justice

In major cities today, there are neighborhoods that have been continually underserved and as a result are in decay. Private investors and developers turn to these particular neighborhoods, propose large developments that gentrify these areas, displacing communities and with them their social, political, and economic issues. The purpose of this thesis is to analyze South West, Baltimore, a community composed of 8 neighborhoods on the verge of being gentrified, by incoming development. Through investigating the key issues present in this community for many years, this thesis will attempt to develop a catalytic environment, which will facilitate change within the community by providing a place for its members to help tackle these issues, improving their circumstances, and the circumstances of the neighborhoods they form part of.

Perceptions of New Principal Mentoring Programs in a Large Urban School District

The principalship has changed significantly over the past 20 years. Today’s principals must be effective instructional leaders, managers of large facilities, and experts at analyzing data to successfully meet the accountability demands of high-stakes testing, along with state, and federal mandates. The primary purpose of this quantitative study was to examine how 43 first- and second-year sitting school principals perceived their mentoring experiences and the degree to which a principal mentoring program—offered by their large urban school district—was effective in building their leadership capacity. A second purpose of this inquiry was to understand these principals’ perceptions of the most beneficial aspects of the mentoring program. The study used quantitative data gathered via an online questionnaire distributed during Fall 2015. The results indicated that respondents perceived that the components of the large urban school-mentoring program were generally effective in training principal mentees to become highly-effective school leaders. This study enriches the literature on mentoring by providing the voices of first and second year school leaders to add depth to the characteristics of successful mentoring programs.