On the origin of photocarrier losses in Iron Pyrite nanocubes: Charge carrier dynamics and electrical transport study

Iron Pyrite has received a lot attention of the researchers to develop low cost and non-toxic solar energy conversion system. Despite of having a band gap of 0.95 eV and extraordinarily high optical absorption, the efficiency is hampered by photovoltage loss. Maximum photovoltage achieved so far could not exceed more than 200 mV. We addressed this problem by identifying photocarrier loss pathways within the high quality, faceted iron pyrite nanocubes prepared by hot-injection method. In this work, we probed charge carrier dynamics by ultrafast laser spectroscopy and analyze the carrier relaxation/recombination lifetimes. We have also analyzed the impact of defects on transport properties of pyrite. To further examine the nature intrinsic defects in iron pyrite, we did low temperature magnetic measurements and found the evidence of phase impurities that relate to sulfur vacancies. On the basis of comprehensive characterization and analysis of the system, we presented a model that explains the origin of low photovoltages in iron pyrite. Fast carrier localization to shallow states followed by deep level relaxation is found to be the main cause. The elimination of the problem lies in preparing samples with clean band gap and passivating intrinsic defects.