Interface Optimization Of The Perovskite Solar Cells

Perovskite materials have become star materials in the fields of photovoltaics and electroluminescence due to their unique properties such as direct band gap,high absorption coefficient,narrow band gap and high defect tolerance.The power conversion efficiency of perovskite solar cells increased rapidly from 3.8%to over 24%in past decade,mainly based on component engineering,perovskite film growth control and perovskite/transport layer interface engineering.It could be said that the interface plays a decisive role on the efficiency and stability of the device,because the formation and dissociation of exciton pairs,carrier injection and recombination,energy level position matching and ion migration are directly related to the interface or grain boundary.Optimization of the interface of perovskite solar cells and improvement of film crystallinity are essential methods to improve the comprehensive performance of perovskite solar cells.Based on the inverted structure of the devices,we developed a pulsed water vapor post-treatment process based on the atomic layer deposition equipment.The MAPbI₃/PbI₂ bilayer structure was constructed via in situ decomposition of the perovskite film surface.The position of PbI₂ is precisely controlled and its role in different device structures is analyzed in detail.The study found that in the normal devices,the improvement of device performance is mainly due to the passivation of PbI₂to surface defects,and the device efficiency increased from 19.47%to 20.38%.More significantly,in addition to passivating surface defects,the role of the lead iodide layer plays the dominated role of energy level matching in the inverted structured devices,promoting electron injection and preventing carriers reverse recombination.Thus the Voc of the inverted device increased from 1.05 V to 1.13 V,which is the highest value of the MAPbI₃/PCBM based inverted perovskite solar cells.In the normal device structure,we have carried out detailed research on the traditional SnO₂ electron transport layer and found that the film formation of the SnO₂electron transport layer can be effectively improved by a suitable solification process.The Chlorine element can be introduced on the surface of SnO₂ through different annealing temperatures.In this way,the ion exchange at the interface can spontaneously passivate some defects of the interface between the perovskite and SnO₂ ETL,improve the bonding between the electron transport layer and the perovskite layer in the planar device structure.On the other hand,the chlorine element which was exchanged into the perovskite films also promotes the longitudinal crystal growth of the crystal grains during the subsequent diffusion sublimation process.Therefore,we increased the voltage of the formal device to 1.19 V through the synergy effects of in-situ ion exchange and MACl promoting film crystallization,which is one of the highest voltages based on the MAPbI₃ system,and the device efficiency reached 20.32%.