Study On Crystallization Process Regulation And Device Encapsulation Of Printed Mesoscopic Perovskite Solar Cells

Metal halide perovskite solar cells（PSCs）represent one of the most outstanding high-efficiency thin-film solar cell technologies to date,with great potential for low-cost photovoltaic device fabrication via facile solution-processing strategies.Printed mesoscopic PSCs prepared by scalable screen-printing technology are considered to be one of the current perovskite photovoltaic technologies closest to commercial application and have broad market application prospects due to their excellent stability,significant cost advantages and easy large-area preparation.Printed mesoscopic PSCs utilize low-cost and scalable printing technology,while eliminating expensive hole transport materials and noble metal electrode materials,which not only brings significant cost advantages to printed mesoscopic PSCs,but also makes such PSCs exhibit relatively low power conversion efficiency（PCE）compared to PSCs with traditional structures.Around 2018,the average PCE of printed mesoscopic PSCs prepared based on MAPb I₃ perovskite and N,N-dimethylformamide（DMF）/Dimethyl sulfoxide（DMSO）mixed solvent system was only about 12%.The morphology and structure of perovskite films fundamentally affects the performance of corresponding PSCs.Due to the complexity of the unique three-layer mesoporous thick film device structure of printed mesoscopic PSCs and its stacking thickness of more than 10μm,it brings severe challenges to the uniform filling and crystal growth of perovskite precursor solution.The most widely used perovskite precursor solution is a strongly polar mixed solvent system based on DMF/DMSO.This solvent system also has a high boiling point and usually requires an annealing temperature of≥100℃.The rapid volatilization of the mixed solvent during high temperature annealing can easily lead to the poor crystallization quality of perovskite films in the three-layer mesoporous thick film structure,which restricts the improvement of device performance.Therefore,the key scientific and technical problem to improve the performance of printed mesoscopic PSCs is how to regulate the crystallization process of perovskite in the three-layer mesoporous thick film structure by effective means to obtain high-quality perovskite films.In this paper,the crystallization process of perovskite is regulated by additive engineering to fabricate high-quality perovskite films to improve the device performance of printed mesoscopic PSCs.Then,reliable device encapsulation technology was explored to improve the outdoor operation stability of printed mesoscopic PSCs.The main research contents are divided into the following four parts:（1）Lewis base biuret with both carbonyl（C=O）and amino（-NH₂）bifunctional groups was introduced into MAPb I₃ perovskite as an additive.Printed mesoscopic PSCs modified by bifunctional Lewis base biuret were prepared by one-step drop coating method.The PCE was successfully increased from 10.66%to 13.42%.The results show that there is a strong coordination between biuret and perovskite.The addition of biuret can not only regulate the crystallization process of MAPb I₃ perovskite in three-layer mesoporous thick film structure,but also crosslink with non-coordinated ions in adjacent perovskite after annealing to passivate defects.This synergy promotes the growth of high-quality MAPb I₃ perovskite films in the mesoporous structure,effectively inhibits the carrier recombination in the device,and finally improves the device performance of printed mesoscopic PSCs.（2）The green methylamine acetate（MAAc）ionic liquid was introduced into MAPb I₃perovskite as an additive,and printed mesoscopic PSCs based on MAAc ionic liquid were prepared by one-step drop coating method,and the PCE was successfully increased from the original 10.90%to 13.54%.The study shows that the synergistic effect of MA⁺and Ac^-of MAAc affects the chemical environment of perovskite precursor solution.Ac^-preferentially combines with Pb I₂ during the film annealing process to form a MAPb I_3-x（Ac）_x perovskite-like intermediate,which effectively regulates the crystallization process of MAPb I₃perovskite in the three-layer mesoporous thick film structure,and perovskite films with high crystallinity,low defect density,and dense mesopore filling was prepared,which finally improved the PCE and stability of printed mesoscopic PSCs.（3）Using Cs_0.1Rb_0.05FA_0.85Pb I₃ mixed cation perovskite as a more efficient photoactive layer,and introducing acetamide as an additive,through the synergistic strategy of component engineering and additive modification,the PCE was successfully increased from the original 14.66%to 16.22%.The study shows that the broad spectral absorption capacity of Cs_0.1Rb_0.05FA_0.85Pb I₃ perovskite and the enhancement effect of Cs and Rb on the stability of FA-based perovskite make the printed mesoscopic PSCs based on Cs/Rb/FA perovskite have higher performance potential.In addition,the amide group in acetamide can effectively regulate the crystallization process of Cs_0.1Rb_0.05FA_0.85Pb I₃ perovskite in the three-layer mesoporous thick film structure,and acetamide can effectively passivate the uncoordinated ion defects in perovskite films after annealing.Under the synergistic effect of component engineering and additive modification,Cs/Rb/FA perovskite films with broad spectral absorption range,high crystal quality,and few film defects were prepared in the three-layer mesoporous thick film structure,which finally greatly improved the device performance of printed mesoscopic PSCs.（4）The printed mesoscopic PSCs based on Cs_0.1Rb_0.05FA_0.85Pb I₃ perovskite exhibited excellent device performance,then the device encapsulation research was carried out using ultraviolet（Ultraviolet rays,UV）curing adhesive.Studies have shown that the"blanket-seal"encapsulation structure will have a serious negative impact on the performance of perovskite films and devices.Therefore,the"side-seal"encapsulation structure is preferred for UV-curing encapsulation of printed mesoscopic PSCs.The adoption of UV-curing“side-seal”encapsulation technology significantly improves the water stability of the printed mesoscopic PSCs,thereby improving their outdoor operational stability.