An Investigation into Electric Field-Modulated Photoluminescence of Perovskite solar cells
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An Investigation into Electric Field-Modulated Photoluminescence of Perovskite solar cells Zhihua Xu1 Department of Chemical Engineering, University of Minnesota Duluth, Duluth, MN 55812, U.S.A.
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ABSTRACT Electric field-modulated photoluminescence (PL) of perovskite solar cells is investigated to gain deeper insight about the role of the mobile ions in organometal halide perovskites. The PL intensity of perovskite solar cells show significant dependence on the polarity of the external electric field and the voltage scanning direction. This phenomenon is discussed in the framework of an ion migration mechanism, which has been widely accounted for the current density-voltage (J-V) hysteresis in perovskite solar cells. The result suggests that the mobile ions not only change the internal electric field of perovskite solar cells, but also have an effect on the recombination of photogenerated charge carriers. INTRODUCTION Perovskite solar cells (PSCs), which utilize organometal halide perovskites (OHPs) as the light-harvesting materials, have gained increasing interest as a cost-effective alternative to silicon solar cells [1-5]. One interesting yet puzzling finding with PSCs is the presence of current density-voltage (J-V) hysteresis, i.e., the J-V characteristics and power conversion efficiency (PCE) of a specific perovskite solar cell varies with the voltage sweeping direction [6]. Although the origin of the J-V hysteresis in PSCs have been explained by different mechanisms such as ferroelectric polarization, capacitive effects and charge trapping, more and more recent researches have suggested that the migration of mobile ions in OHPs plays a dominant role for the J-V hysteresis in PSCs [7-10]. However, the exact nature and the roles of the mobile ions in PSCs remain unclear. Some recent researches have suggested that the mobile ionic species might be related to charge trapping and nonradiative recombination processes [11, 12]. Photoluminescence (PL) spectroscopies have been utilized to investigate ion migration in OHPs thin films sandwiched by noninjecting or symmetric contacts, and the results suggest certain links between PL intensity and ion migration in OHPs under an external electric field [13-16]. To further clarify the roles of ion migration, we conducted electric field-modulated PL characterizations for perovskite solar cells with a typical mesoscopic architecture, where the intrinsic built-in electric field resulted from asymmetric contact could potentially modify the ion distribution and their migration dynamics under external electric field. EXPERIMENTAL METHOD The fabrication of mesoscopic perovskite solar cells starts with spin-coating of 2M TiCl4 solution on pre-cleaned Fluorine-doped SnO2 (FTO) glass substrate followed by heating at 500oC for 20 min to yield a compact TiO2 layer with thickness of 50nm. Then a mesoporous TiO2 film is deposited on top of the compact-TiO2 layer by spin-coating a Dyesol NR18T TiO2 paste (diluted with terpineol and ethanol) followed by annealing at 500 oC for 40 min in
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