Study Of The Electron And Ion Charge Dynamics In The Perovskite Solar Cells

Photovoltaic technology is an important approach to solve the increasingly serious energy and environmental problems.It is beneficial for achieving a more perfect energy consumption structure and a sustainable development.It is always a research topic to develop lower-cost and higher-efficiency solar cells for application.For this ultimate purpose,three generations of solar cells have been developed,such as the crystalline silicon and GaAs,thin film heterojunction and the emerging solar cells.Perovskite solar cell is one of the emerging solar cells that has appeared in recent years and has experienced rapid improvement in its performance.Solution deposited perovskite polycrystalline thin film?e.g.CH₃NH₃PbI₃,CH?NH₂?₂PbI₃ and their alloy compounds?has high light absorption coefficient?¹05 cm-1?,low defect density?¹016 cm-3?and relative long carrier diffusion length.Based on these outstanding semiconductor properties,high-quality film deposition and design of device structure and interface,the efficiency of the small-area cell has been improved to 22.1%,comparable to the commercialized ones.However,challenges in stability and large-area industrial production still exist.On the other hand,debates about the intrinsic nature of the perovskite material and device?e.g.excitonic VS.nonexcitonic and sensitized VS.heterojunction?and anomalous photoelectric behaviors also exist during the efficiency enhancement process.Therefore,we paid efforts on clarifying the fundamental and critical physics properties of this cell from the perspective of electron and ion charge dynamics.Meanwhile,higher device performance has been achieved by controlling the charge dynamics.The typical research achievements are summarized as following:?1?By the dissolving-recrystallization process,a dense and smooth PbI₂ film and high-quality perovskite thin film have been prepared.Based on this film,the efficiency of the hole transport material-free perovskite solar cell has been promoted to exceeding 10% for the first time.Further by control the perovskite film deposition,another world-highest efficiency of 11.4% was achieved at that time.?2?By the DC current-voltage,AC impedance and capacitance analysis,the junction nature of the cell has been investigated.It is found that the cell is a typical heterojunction solar cell with outstanding junction properties.?3?By theoretical calculations,the back surface recombination is found to be a critical process to limit the efficiency of this cell.To suppress this recombination and to control the charge transport in the cell,a metal-insulator-semiconductor?MIS?back contact structure has been designed and experimentally realized by atomic layer deposition method.Finally,the average efficiency of the cell is enhanced from 8.6% to 10.1%.?4?An ‘electrical pump-photoelectric probe' method has been developed to investigate the microscopic charge transport and recombination properties behind the hysteresis in the cell.It is found that the electric field inside the cell would experience evolutions in direction and strength during the time-dependent photocurrent and photovoltage behaviors.Both the interfacial doping and defect induced by the redistribution of ion charge is the intrinsic physics origins for these hysteresis phenomena.?5?By designs of system structure and electric circuit,a modulated transient photocurrent and photovoltage system has been developed to probe the charge dynamics of the solar cells when they work in different electrical and optical conditions.Moreover,based on fundamental semiconductor physics,physics models and analysis methods have been proposed to adequately derive critical information about the cell from the transient signals.