Chris Leighton, University of Minnesota
Potential Resolution to the “Doping Puzzle” in Pyrite FeS2: Carrier Type Determination by Hall Effect and Thermopower
Written by Ahmad R. Kirmani
As the race toward a cost-effective solar energy conversion technology heats up, the need to better understand the fundamental questions at the heart of these promising technologies takes center-stage. One such interesting technology is based on pyrite iron sulfide (FeS2) as the absorber. The interest and potential in this not-much-pursued photovoltaics lies in its earth-abundance, non-toxicity, low-cost, and optimal bandgap. However, since the metric of power-conversion efficiency (PCE) rules the photovoltaics sector, interest in FeS2 has declined owing to sub-standard PCEs, making it a failed photovoltaic technology. Low voltages are a scourge to these solar cells and an inability to effectively dope them has led to the downfall.
Chris Leighton and his team at the University of Minnesota hope to revert this trend. Leighton feels that an efficient control over doping requires a deeper understanding of the doping mechanism in this material that the community has so far lacked. Harkening back to the widely-held misunderstandings on doping of FeS2 single crystals and thin films, the team took a fresh look employing a suite of characterization techniques. The findings suggest a rethink on the widely-accepted notion that these thin films are predominantly p-type. Furthermore, the team suggests that sulfur vacancies might, in fact, be responsible for doping in this photovoltaic material.
These key findings from the Leighton group are potentially game-changing and provide crucial design rules for a cost-effective and non-toxic pyrite FeS2-based photovoltaic technology.