Research On Mixed-ion-type Perovskite Solar Cells Prepared By Vapor Assisted Solution Process And Its Performance

The organic-inorganic halide perovskite material is a novel material with advantages of high extinction coefficient,excellent carrier transport and long carrier diffusion length.The perovskite light absorbing layer is the core part of the whole device and plays a decisive role in the photovoltaic performance of the device.The quality of the perovskite absorbing layer plays a decisive role in the photovoltaic performance,therefore it is one of the important ways to promote the development of PSCs to adopt a suitable preparation process,study the perovskite growth process and explain the key factor affecting the perovskite crystal.Generally,the preparation methods include solution process,dual-source vapour deposition process and vapor assisted solution process(VASP).Compared with solution process,vapor reaction can effectively avoid solvation and hydrolysis and reduce the resulting compound structure.The reaction rate can be control by adjusting the reaction conditions of vapor reaction and obtain uniform thin films.Moreover,vapor reaction is different from the solution process in the film growth kinetics and thin film growth mechanism,so it is necessary to study the preparation of PSCs by vapor reactions.In this paper,the key factors affecting perovskite structure are systematically studied.Then clarified the growth perovskite mechanism and realized its structure controllable.Through the research on the photoelectric performance of solar cells,the relationship between PSCs performance and perovskite films is revealed,so that the influence mechanism of carrier transport inside the PSCs is mastered,which lays a foundation for obtaining highly efficient and stable perovskite solar cells.The stable a-FAPbI3 prepared by VASP,and the MA+has been introduced into FAPbI3 crystal lattice to form the mixed cation perovskite FAxMA1-xPbI3 effectively mixing FAI and MAI in vapor deposition.The influence of MA+on film quality and device performance has been investigated systematically.The morphology of FAxMA1-xPbI3 films was smooth and compact,and the carrier lifetime improved greatly.The optimal power conversion efficiency(PCE)16.48%has been obtained based on FAxMA1-xPbI3 devices with 40 wt%MAI mixed with a FF of 73.56%,a JSC of 22.51mA/cm2 and a VOC of 1.00 V.At the same time,using VASP,the inorganic Cs+ has been successfully introduced into FAPbI3 to form FAxCs1-xPbI3.To improve the devices performance,the ion exchange process and pre-deposited seed layer process has been developed respectively.Firstly,FACl was introduced to optimize the growth and crystallization of perovskite by controlling the nucleation and crystallization rate.And the high quality perovskite film FA0.9Cs0.1PbI3 possessed low radiation recombination,long carrier lifetime and low defect density was obtained.The improvement of perovskite film resulted in a significant increase in VOC as well as FF.The optimal device PCE reached 16.39%(VOC=0.99 V,JSC=22.87 mA/cm2,FF=74.82%)and the hysteresis effect and stability of corresponding devices has also been improved significantly.Besides,the device performance of FA0.9Cs0.1PbI3;has been improved by a pre-deposited seed layer before vapor deposition.The perovskite films with enlarged grain sizes,prolonged carrier lifetime and low defect density were obtained.And the corresponding device performance with a PCE of 16.17%,a VOC of 0.99 V,a JSC of 22.55 mA/cm2,a FF of 71.84%Introducing halogen and pseudo-halogen has been one of the effective strategies to improve the photovoltaic performance of PSCs.In this thesis,planar heterojunction PSCs based on PbI2,PbBr2 and Pb(SCN)2 were fabricated through VASP.The effect of the Br-and SCN-on the evolution of the crystal structure,film growth kinetics,electron lifetime,defect density and photoelectric performance were systematic studied.Although the ultima product in the three films was CH3NH3Pbi3,the crystal growth kinetics was absolutely different.The intermediate perovskite phase CH3NH3PbIxBry was formed during the preparation of CH3NH3PbI3 by PbBr2,and the earlier nucleation regulated the perovskite growth rate effectively.However,the formation of CH3NH3PbI3 began until Pb(SCN)2 was completely converted to PbI2.These differences indeed strongly affected the films morphologies,defect density,electronic lifetime and photovoltaic performance of the devices.All the results indicated that the quality of perovskite film based on Pb(SCN)2 was inferior and the corresponding devices showed obvious deterioration in photovoltaic performance compared to that of PbI2 and PbBr2.Some physical mechanisms have been explained by studying the photoelectric feature of the devices.