nn6b00065_si_001.pdf (998.9 kB)
Origin of Photocarrier Losses in Iron Pyrite (FeS2) Nanocubes
journal contribution
posted on 2016-03-10, 00:00 authored by Sudhanshu Shukla, Guichuan Xing, Hu Ge, Rajiv
Ramanujam Prabhakar, Sinu Mathew, Zhenghua Su, Venkatram Nalla, Thirumalai Venkatesan, Nripan Mathews, Thirumany Sritharan, Tze Chien Sum, Qihua XiongIron pyrite has received significant
attention due to its high
optical absorption. However, the loss of open circuit voltage (Voc) prevents its further application in photovoltaics.
Herein, we have studied the photophysics of pyrite by ultrafast laser
spectroscopy to understand fundamental limitation of low Voc by quantifying photocarrier losses in high quality,
stoichiometric, and phase pure {100} faceted pyrite nanocubes. We
found that fast carrier localization of photoexcited carriers to indirect
band edge and shallow trap states is responsible for major carrier
loss. Slow relaxation component reflects high density of defects within
the band gap which is consistent with the observed Mott-variable range
hopping (VRH) conduction from transport measurements. Magnetic measurements
strikingly show the magnetic ordering associated with phase inhomogeneity,
such as FeS2−δ (0 ≤ δ ≤
1). This implies that improvement of iron pyrite solar cell performance
lies in mitigating the intrinsic defects (such as sulfur vacancies)
by blocking the fast carrier localization process. Photocarrier generation
and relaxation model is presented by comprehensive analysis. Our results
provide insight into possible defects that induce midgap states and
facilitate rapid carrier relaxation before collection.