Abstract

Tandem solar cells can achieve higher efficiencies than single junction cells because they can absorb different spectral ranges of sunlight more efficiently using multiple semiconductor bandgaps. I will discuss promising approaches to advance tandem photovoltaics (PV) and the potential for photoelectrochemical applications of these devices. For PV, I will outline the different possible material combinations and electrical/optical interconnections for sub-cells in a tandem device. Each approach has trade-offs in efficiency, cost, manufacturability, and energy yield. While most of the research on tandem PV has focused on 2-terminal (2T) devices, interest in four-terminal (4T) and three-terminal (3T) tandems is growing. 3T and 4T designs offer advantages over 2T, such as avoiding cell polarity restrictions, current-matching, and improving energy yields, but they complicate module circuitry. I will discuss NREL ’s experimental and modeling approaches to understand the most promising tandem options. Multi-terminal devices also enable new applications outside of traditional electricity generation. The direct use of semiconductors to drive photoelectrochemical reactions is a promising approach create liquid/hydrocarbon products that can be used as fuels or chemical feedstocks without relying on traditional petrochemical processes. I will show how 3T photoelectrodes can improve device stability under day/night cycling, and how tandem devices based on III -V semiconductors can be used to drive cascade chemical reactions by creating multiple catalytic microenvironments in a single photoelectrochemical device.

Bio: Emily Warren is a research group manager and senior scientist at the National Renewable Energy Laboratory, in Colorado, USA where she leads the Performance and Tandems group, that focuses on the fabrication and measurement of high efficiency photovoltaic devices. Her research interests include optoelectronic modeling of tandem solar cells, heteroepitaxy of III -Vs on Si, and the photoelectrochemical production of solar fuels. Her work helps to push the boundaries of what is possible for converting solar energy into usable energy. She received her PhD from the California Institute of Technology, an MPhil from the University of Cambridge in Engineering for Sustainable Development, and a bachelor’s degree in chemical engineering from Cornell University