title: Origin of Photocarrier Losses in Iron Pyrite (FeS2) Nanocubes.
abstract: Iron 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.
authors.forename: Sudhanshu
authors.initials: S
authors.lastname: Shukla
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , Singapore 637371, Singapore.
authors.forename: Guichuan
authors.initials: G
authors.lastname: Xing
authors.forename: Hu
authors.initials: H
authors.lastname: Ge
authors.affiliation: Energy Research Institute, Nanyang Technological University , Singapore 637371, Singapore.
authors.forename: Rajiv Ramanujam
authors.initials: RR
authors.lastname: Prabhakar
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore , Singapore 117576, Singapore.|NUSNNI-NanoCore, National University of Singapore , Singapore 117576, Singapore.
authors.forename: Sinu
authors.initials: S
authors.lastname: Mathew
authors.affiliation: Energy Research Institute, Nanyang Technological University , Singapore 637371, Singapore.
authors.forename: Zhenghua
authors.initials: Z
authors.lastname: Su
authors.affiliation: Centre for Disruptive Photonic Technologies (CDPT), Nanyang Technological University , Singapore 639798, Singapore.
authors.forename: Venkatram
authors.initials: V
authors.lastname: Nalla
authors.affiliation: Department of Electrical and Computer Engineering, National University of Singapore , Singapore 117576, Singapore.|NUSNNI-NanoCore, National University of Singapore , Singapore 117576, Singapore.
authors.forename: Thirumalai
authors.initials: T
authors.lastname: Venkatesan
authors.forename: Nripan
authors.initials: N
authors.lastname: Mathews
authors.forename: Thirumany
authors.initials: T
authors.lastname: Sritharan
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , Singapore 637371, Singapore.
authors.forename: Tze Chien
authors.initials: TC
authors.lastname: Sum
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University , Singapore 637371, Singapore.|NOVITAS, Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University , Singapore 637371, Singapore.
authors.forename: Qihua
authors.initials: Q
authors.lastname: Xiong
keywords: carrier dynamics; iron pyrite; magnetization; nanocubes; photovoltaics; transient absorption; variable range hopping