Thin Film Photovoltaics from Earth Abundant Materials: The Good, The Bad and The Promise
IBM TJ Watson Research Center, Yorktown Hts., NY
Numerous requirements are imposed on photovoltaic (PV) materials subject to their specific applications but, above all, efficiency is of paramount importance. Beyond that, a multitude of issues loom, including availability and toxicity of the constituent elements, overall cost and industrially efficient fabrication methods. While arguably no one particular PV technology provides a complete solution to these myriad issues, earth abundant multielement thin film absorbers such as CZTS,Se- Cu2ZnSn(SxSe1-x)4 and its variants are a group of materials that hold great promise but present significant challenges. The hope is that these absorbers can be utilized to reach terawatt level, solar based renewable energy generation. But, as we have discovered, the high density of intrinsic bulk defects limits achievable open circuit voltage (Voc) and efficiency. In this talk I will review the status of our knowledge of performance limiting defects and describe several approaches we have taken to solve these problems. These include elemental substitution to reduce intrinsic defects and re-engineering of the back contact to drive higher voltages. I will describe the use of femtosecond UPS/photovoltage spectroscopy to extract band alignments at both the front and back surfaces, critical to high performance. I will also describe Auger nanoprobe studies of grain boundaries and the opportunity to utilize the imaging capabilities at STROBE to gain greater insight into these critical interfaces. Finally, I will describe our most recent work to increase Voc of individual devices and our development of a monolithic, series-connected array to achieve > 5.5V for powering autonomous devices for the “Internet-of-Things”.
The talk will be from 2-3pm MT.
Refreshments, Question & Answer session from 3-4pm MT.