Origin of Photocarrier Losses in Iron Pyrite (FeS2) Nanocubes

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• 作者：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 Xiong
• 刊名：ACS Nano
• 出版年：2016
• 出版时间：April 26, 2016
• 年：2016
• 卷：10
• 期：4
• 页码：4431-4440
• 全文大小：565K
• 年卷期：0
• ISSN：1936-086X

文摘

Iron pyrite has received significant attention due to its high optical absorption. However, the loss of open circuit voltage (V_oc) prevents its further application in photovoltaics. Herein, we have studied the photophysics of pyrite by ultrafast laser spectroscopy to understand fundamental limitation of low V_oc 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 FeS_2−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.