Grain Boundary Modification And Stability Of Printable Mesoscopic Perovskite Solar Cells

Owing to their excellent optoelectronic properties and superior device performance,perovskite materials have received extensive research attention,which has become the most powerful competitor in the next generation of photovoltaic devices.In just a few years,the photoelectric conversion efficiency（PCE）of perovskite solar cells（PSCs）has leapt from the initial 3.8%to the certificated 25.5%,which has exceed the highest PCE of polycrystalline silicon solar cells.However,PSCs with the highest PCE requires a complicated preparation process,harsh working environment and expensive materials,which to some extent hinders the industrialization and commercialization of high-efficiency PSCs.The search for a device structure with simple structure,mild preparation conditions and large area preparation has become a problem that needs to be solved urgently.To reduce costs and optimize the device structure,the hole-conductor-free,printable mesoscopic perovskite solar cells（MPSCs）came into being.The entire device is prepared in ambient air by using simple screen printing technology.It is expected to realize industrialization and commercialization with the potential for large-scale production.Although the device structure and manufacturing process exhibit great potential for commercial applications,it is still challenging to realize free infiltration of the perovskite precursor into a three-micron mesoporous structure by one-step drop casting method,which may cause incomplete filling and other deficiencies in the active layer.The incomplete filling of the perovskite precursor hinders the extraction of charges and significantly improves the recombination of carriers,thereby greatly reducing the PCE and stability of the device.In response to the above problems,a lot of research have done to improve the PCE and device stability of the MPSCs.The specific work includes the following parts:（1）The fabrication of MPSCs is still a major challenge because it is difficult to realize the free diffusion of precursors throughout the micrometer-scale porous structure.Here,a facile and efficient additive manufacturing technique is proposed with melamine hydroiodide（MLAI）as an additional material.We systematically investigated the impact of MLAI on the crystallization,morphology,and defects of the perovskite film and the performance of the MPSCs.The results revealed that the MLAI effectively optimized the morphology of perovskite and improved the pore-filling as well as passivated the defects of the perovskite film,thus hysteresis was reduced and the performance of the devices was enhanced.Based on the addition of MLAI,the PCE was obtained as 13.86%,which was 18.5%higher than that of the additive-free device.（2）For MPSCs,the wettability of the perovskite precursor is one of the most crucial factors that determine the performance of MPSCs.However,it is difficult to achieve free and efficient diffusion of perovskite precursors in micron-scale porous structures.Here,D-sorbitol hexaacetate（DSHA）was introduced as an additive into perovskite precursor to improve the wettability of the perovskite precursor in the mesopores layers.As a consequence,a PCE of 14.33%was finally obtained,and the stability of the device was significantly improved.The results show that the introduction of DSHA improves the wettability of the perovskite precursor in the mesoporous layer and improves the pore filling.In addition,the presence of carbonyl groups passivates the defects of the perovskite,which significantly improves the performance of the device.It is worth noting that,the unencapsulated device can still maintain 93%of its initial efficiency after 45 days in air with a humidity of 50±5%,while the control device can only maintain 80%of its initial efficiency after only 15days.（3）Methylamine（MA）and methylamine hydrochloride（MACl）are widely used to prepare highly efficient and stable PSCs.However,MA,as a gas,is difficult to handle and inevitably leads to a large amount of escape,and it is difficult to quantitatively calculate.Here,selecting a mixture solvent of methylamine ethanol solution（MA-EtOH sol）and acetonitrile（ACN）as a solvent,a new strategy for preparing MPSCs at room temperature was first proposed.With the introduction of20 mol%MACl as additives,the MPSCs are fabricated without any post-treatment at room temperature via one-step drop-coating method.As a consequence,the average power conversion efficiency（PCE）of 14.73±0.3%（0.1 cm²）with almost no hysteresis is achieved.Most importantly,the device also exhibits excellent long-term stability when it is unencapsulated.Specifically,the unencapsulated device still retain nearly 100%of their original PCE after 64 days and retain 88%after 81 days of storage in the dark with a humidity of 50±5%in an atmospheric environment.It provides a new idea for constructing MPSCs at room temperature in the future.（4）MPSCs with the Cs_0.1Rb_0.05FA_0.85Pb I₃ as light absorbing layer has made breakthrough progress,but its follow-up research is scarce.It is a feasible strategy to realize the passivation of the defects of the perovskite crystal through the carbonyl group and the cross-linking method to improve the stability of the device.Based on this,we propose a strategy by using pentaerythritol tetra（3-mercaptopropionate）（PETM）and pentaerythritol tetraacrylate（PTTA）as additives to carry out click chemistry crosslinking at the perovskite grain boundary,so that the PCE and stability of the device can be significantly increased.The results show that the introduction of PETM and PTTA increased the crystallinity of the perovskite,improved the absorbance of the perovskite film,and improved the wettability of the perovskite precursor.PETM and PTTA can not only be used as crosslinking agents to improve device stability,but also can effectively passivate perovskite defects,reduce the probability of recombination,and significantly improve device efficiency.