Research On Impedance Characteristics In Perovskite Solar Cells

The issue of energy has always been the focus of attention in the 21st century,because energy is a huge driving force for the development of human civilization.With the development of the times,new energy has been developed and utilized.Especially in recent years,everyone has paid more attention to the exploration of clean energy that is beneficial to future development.Solar energy has become the focus of scientific researchers because of its inexhaustible and inexhaustible characteristics.Perovskite solar cells have emerged as the times require.The preparation process of perovskite solar cells is simple,and the required materials are easy to obtain,so in just ten years,its photoelectric conversion efficiency has exceeded 25%from 3.8%in 2009 to 2020,and the development is very rapid.Although the efficiency of perovskite solar cells continues to improve,research on the physical characteristics of photovoltaic devices is not enough,especially some special photoelectric behaviors;this is very unfavorable for the further development of perovskite solar cells.In this paper,some special photoelectric behaviors of perovskite solar cells including current hysteresis,light infiltration,and negative capacitance are mainly studied through electrochemical impedance spectroscopy.The specific research content is as follows:1.Under operating conditions,hysteresis effects and light soaking are observed in organometallic halide perovskite solar cells(PSCs),which hinders accurate assessment of battery power output.Our research suggests that the phenomenon of light soaking is related to the electron selective layer/perovskite interface in hysteresis-free PSCs.The introduction of [6,6]-phenyl C61-butyric acid methyl ester(PC₆₁BM)doped with CH₃NH₃I molecule as an interface layer can effectively release or eliminate this effect,while having the best stable output efficiency and high fill factor.The capacitance-voltage(C-V)and capacitance-frequency(C-f)curves obtained by electrochemical impedance spectroscopy indicate that the light soaking phenomenon in PSCs mainly originates from the charge accumulation at the PC₆₁BM/perovskite interface.The CH₃NH₃I doped in PC₆₁BM prevents ion movement between perovskites and at the same time enhances the charge transfer effect at the interface,thereby eliminating the phenomenon of light soaking.In addition,a model combining ion migration and charge accumulation process to explain the light soaking phenomenon and performance improvement in PSCs is also proposed.2.The phenomenon of negative capacitance often occurs during the measurement of the impedance characteristics of perovskite solar cells,but the cause of negative capacitance has been under debate.In this paper,we use different structures of inverted devices to measure their Nyquist diagrams under different bias voltages,and find that the negative capacitance phenomenon is particularly obvious when the bias voltage is close to the open circuit of the device and the device performance is poor.We believe that this phenomenon is closely related to the PC₆₁BM electron transport layer.When the bias voltage is applied to both ends of the device and the bias voltage is continuously increased,the built-in electric field of the device will be cancelled.When the built-in electric field is completely canceled,the ions will move in the opposite direction,resulting in an abnormal negative capacitance phenomenon.Because the device with good performance has relatively few free ions,and the PC₆₁BM/perovskite interface has a certain adsorption effect,there is no negative capacitance phenomenon.There are a large number of ions in the perovskite material in the device with poor performance.The PC₆₁BM/perovskite interface has a limited ability to adsorb ions.When the applied electric field is large enough to offset the built-in electric field,the ions will move in the opposite direction,thereby there is a phenomenon of negative capacitance.For this explanation,we need to do further exploration and assist the experiment to verify.