Position: Postdoctoral Researcher

Current Institution: University of California, Berkeley

Material and Device Innovations for Energy Applications

The energy landscape has significantly changed within the last few years with photovoltaics reaching grid parity and becoming competitive with traditional sources of energy in many parts of the world. However, further improvements in the overall economics remain key to continue and accelerate this transition towards a sustainable energy production. The most commonly used metric for energy cost is $/Watt. Consequently, either efficiency improvement or manufacturing/material cost reduction can lead to an overall cost drop. To achieve this, novel materials, new fabrication process schemes, and innovative device concepts and architectures are needed.

Thin film solar cells represent one route of cost reduction by using direct band gap materials, that absorb light efficiently within 1-3 um, reducing the thickness requirement to a hundredth of a Si cell. Additionally, such thin film materials can be deposited on flexible substrates opening a new market for flexible modules. I will present my work on new thin film solar cell devices based on a spectrum of different material systems, each presenting unique opportunities and challenges. Specifically, I worked on three material classes and device architectures: First, chalcopyrite based semiconductors for thin film solar cells using earth abundant elements. The focus here is on low cost solution processing as well as the influence of sodium on electrical performance and grain growth. Second, innovative growth processes that make better use of precursor elements can lead to a cost reduction. I will show a novel thin film vapor-liquid-solid (TF VLS) growth platform to process high quality III-V semiconductors for the application in electronic devices and solar cells. The TF VLS platform enables the growth of any desired shape onto non-epitaxial substrates as well as the simultaneous growth and doping of the material which makes it highly versatile for novel device applications. Third, another approach to lower the cost of solar electricity is to increase the solar conversion efficiency. The design of multijunction solar cells presents a promising route to exceed the theoretical Shockley Queisser limit of ~33% for single junction photovoltaic devices. The efficiency of the traditionally well-established Si technology can be significantly raised by stacking a wide gap top cell onto the smaller gap Si bottom cell, thus making better use of the solar spectrum enabling conversion efficiencies > 40%. In this context, the hybrid, organic-inorganic lead halide perovskites are very attractive due to their ease in processing with low-cost equipment and high conversion efficiencies. My contribution to this field is the investigation of the optoelectronic properties of tunable wide band gap lead halide perovskites demonstrating high material quality over the full band gap range from 1.6 – 2.3 eV. This makes the novel hybrid material a highly promising candidate for application in lasers, LEDs, transistors and solar cells.

Carolin M. Sutter-Fella received her Ph.D. from ETH Zürich, Switzerland, where she worked in Prof. Ayodhya N. Tiwari’s laboratory for Thin Films and Photovoltaics. Currently, she is a postdoctoral researcher in Prof. Ali Javey’s group in the Electrical Engineering and Computer Science Department, UC Berkeley. Carolin was awarded a Swiss National Science Foundation Fellowship (2015-2017). Her research is centered around synthesis, characterization and functionalization of inorganic and hybrid organic-inorganic semiconductor materials for energy applications. One of her main interests lies in new photovoltaic materials and devices, with the ultimate goal to make solar power the dominant source of energy. To tackle this challenge, she is working on two objectives – reducing the cost and increasing the conversion efficiency of solar cells. Carolin explores new concepts at the interface of materials engineering and device innovation to enable new applications.