Cyrstallization Control And Interface Modification For High Performance Inverted Perovskite Solar Cells

Inverted planar perovskite solar cells possess huge commercial application promising for low cost,simple preparation process,and matching with large-scale preparation technologies such as screen printing and roll-to-roll.Stability is the biggest obstacle for its application and meanwhile,the power conversion efficiency lags behind that of conventional upright perovskite solar cells.Therefore,improving the efficiency and stability of inverted devices is of great significance for the application and development of perovskite solar cells.This article aims at the current challenges of inverted planar perovskite solar cells,and conducts research from perovskite crystal control,interface layer control,and defect passivation.The main contents are as follows:(1)By modifing the two-step perovskite film preparation process,high-quality perovskite films and high-performance devices have been obtained.By adjusting the stoichiometric ratio of Pb I2 and MAI in the two-step method,the perovskite crystallization behavior was regulated,and a large grain size and high crystallinity perovskite thin film were prepared.The experiment proved that 1.2: 0.3 is the best stoichiometric ratio.The efficiency of the inverted perovskite solar cell prepared based on the optimal ratio is as high as 18.38 %.In addition,the optimal device can maintain 73.85 % and 95.63 % of the initial efficiency when stored in air with 30-50 % humidity and nitrogen for more than 200 hours.(2)The feasibility and unique advantages of non-fullerene acceptor materials(ITIT,ITIC-Th,IT-M)and fullerene acceptor materials(PCBM)as an electron transport layer in inverted planar devices was confirmed by comparing the corresponding energy levels and absorptions.Three non-fullerene acceptor materials were introduced into inverted perovskite solar cells separately,and high-performance device was prepared.Experiment results show that non-fullerenes have excellent film-forming properties on the perovskite surface.The introduction of non-fullerenes optimizes the interface contact between perovskite and electron transport,improves the charge extraction efficiency,therefore,suppresses device hysteresis.In addition,the higher lowest molecule unoccupied orbital energy(LUMO)level of non-fullerenes reduces the charge reorganization loss of device,thus the open circuit voltage and device efficiency were improved.Among the non-fullerene based devices,ITIC-ETL-based undoped device achieved an open-circuit voltage of 1.07 V and a high device efficiency of 14.29 %.(3)The ultra-thin poly(ethylene oxide)(PEO)film was introduced into the inverted planar perovskite device to modify the interfaces of PTAA / MAPbI3 and MAPbI3 / PCBM.It is found through experiments that the introduction of PEO at the interface of PTAA /MAPbI3 helps to enhance the crystallinity of the perovskite and passivate the perovskite defects,thereby reducing the interface charge recombination loss and increasing the open circuit voltage of the devices.The Simultaneous introduction of PEO film at the two interfaces of PTAA / MAPbI3 and MAPbI3 / PCBM ffectively improves the PCBM film-forming property,optimizes the interface contact of MAPbI3 / PCBM,promotes charge transfer,and further passivates the perovskite defects.Finally,the inverted planar perovskite solar cell based on the simultaneous modification of the dual interfaces achieved a high efficiency of 21.46 % and excellent air stability(T80 ≥ 500 h).