This slide highlights our work on one particular earth-abundant absorber, iron pyrite. Pyrite solar cells can produce large photocurrent but suffer from very low photovoltage, the origin of which had long remained a mystery. We used systematic transport studies of pyrite single crystals and thin-films made by gas-phase and molecular ink approaches to demonstrate that this material possesses a conductive, hole-rich surface layer (an inversion layer on n-type crystals) that limits the photovoltage to small values by enabling electrons to tunnel through most of the surface potential barrier instead of going over it. Our work suggests that passivation of this conductive surface layer is key to attaining reasonable photovoltage and power conversion efficiency from pyrite photovoltaics. Controlled bulk doping of pyrite is another major challenge, especially for p-type material. Our combination of comparative studies of high-quality single crystals and thin-films with emphasis on detailed transport measurements, modeling, surface modification and doping is powerful and can be extended to understand other promising but underperforming absorber materials.
An inversion layer at the surface of n-type iron pyrite.
Limpinsel, M., Farhi, N., Berry, N., Lindemuth, J., Perkins, C. L., Lin, Q., Law, M. Energy & Environmental Science, 7, 1974-1989 (2014) PDF Online Article
Atmospheric-pressure chemical vapor deposition of iron pyrite thin films.
Berry, N., Cheng, M., Perkins, C. L., Limpinsel, M., Hemminger, J. C., Law, M. Advanced Energy Materials, 2, 1124-1135 (2012) PDF Online Article
Colloidal iron pyrite (FeS2) nanocrystal inks for thin film photovoltaics.
Puthussery, J., Seefeld, S., Berry, N., Gibbs, M., Law, M. Journal of the American Chemical Society, 133, 716-719 (2011) PDF Online Article
Atomistic modeling of sulfur vacancy diffusion near iron pyrite surfaces.
Zhang, Y. N., Law, M., Wu, R. Q. Journal of Physical Chemistry C, 119, 24859-24864 (2015) PDF Online Article
The effect of surface stoichiometry on the band gap of the pyrite FeS2(100) surface.
Zhang, Y. N., Hu, J., Law, M., Wu, R. Q. Physical Review B, 85, 085314 (2012) PDF Online Article
Iron pyrite thin films synthesized from an Fe(acac)3 ink.
Seefeld, S., Limpinsel, M., Liu, Y., Farhi, N., Zhang, Y. N., Berry, N., Kwon, Y. J., Perkins, C. L., Hemminger, J. C., Wu, R. Q., Law, M. Journal of the American Chemical Society, 135, 4412-4424 (2013) PDF Online Article