In Situ Regeneration Of Perovskite Solar Cells And Mechanism For The Accociated Hysteresis Phenomena

Perovskite solar cells?PSCs?have drawn considerable attentions due to their low cost,high efficiency,and easy fabrication.Power conversion efficiency of perovskite solar cell?PSC?with organic-inorganic lead halide serving as light absorbing layer has reached to 23.7%.Most of the high-efficiency records are achieved by lead-based perovskite solar cells.Due to the toxicity of heavy metal Pb to human body,it is necessary to recycle lead?Pb?in perovskite solar cells during the lifecycle of PSCs.Moreover,perovskite film is sensitive to humidity,temperature,and ultraviolet light,and easy to be degraded by water,light,and heat.It is thus urgent for researchers to explore new ways to regenerate perovskite devices.In this thesis,we work on recovering degraded perovskite devices via in-situ regeneration processing.Upon this method,the recycling of perovskite devices is realized,and the loss of heavy metal lead is reduced.We firstly fabricate a fully degraded perovskite model device by immersing an anti-solvent processed perovskite film into deionized water to decompose perovskite crystals.XRD and SEM results confirm that the resultant lead iodide crystals are stacked on mesoporous TiO₂ film.Lead iodide film is subsequently pretreated with DMF/DMSO/isopropanol mixed precursor solution by spin-coating.Then a mixing halogen solution is spin-coated on the surface of pretreated lead iodide to regenerate perovskite film.This method is shown to transform lead iodide into perovskite crystals completely.The surface film is relatively smooth and compact.XRD results show that the crystals on the regenerated perovskite film are identical to those on the original device.Photovoltaic response measurement shows that the pretreatment of the degraded film with mixing precursor plays a key role in improving power conversion efficiency of the regenerated cells.Moreover,the measurement of open circuit voltage decay shows that the usage of the mixing precursor solution improves electron lifetime of the regenerated perovskite cells and hence reduces the rate of interfacial recombination.A higher open circuit voltage is achieved accordingly.By optimizing the concentration of precursor solution,a power conversion efficiency of 14.5%is achieved for the regenerated devices.The regenerated perovskite cells obtained by in-situ regeneration processing are found to show photocurrent hysteresis,compared with the prestine devices.It indicates that the contact between perovskite layer and mesoporous titanium dioxide layer is also vital to the photovoltaic preformance of the devices.We herein combine the drift-diffusion equations with the Bulter-Volmer?BV?model for simulating dynamics of charge separation of the perovskite solar cell suffering from limited interface charge transfer.The simulation results show that rapid interfacial charge transfer gives rise negligible hysteresis.The occurance of hysteresis phenomenon is mainly attributed to the accumulation of charge carriers and movable ions at perovskite/CSL contact.Besides of the effects of ion motion,we also demonstrate that j-V hysteresis is directly related to the limitation on charge extraction inside perovskite layer.Moreover,the limitation on charge transfer is not the key reason for the loss in open circuit voltage.The photovoltage loss is originated from the recombination at the interface between perovskite layer and CSL,which highlights the key role of retarding recombination on improving photovoltage.