Research On Design And Preparation Of Flexible Grain Boundaries And New Type Encapsulation Material For Perovskite Solar Cells

Wearable devices play an important role in medical monitoring,intelligent life,etc.and have attracted extensive research attention for their advantages like lightweight,portability and adaption to curved surfaces.Dependable flexible energy supply equipment is the guarantee for the stable operation of these kind of electronic devices.Perovskite solar cells（PSCs）are considered to be a promising new generation photovoltaic technology for their characteristics of high efficiency,solution-processbility and low cost.Meanwhile,the crystallinity of perovskite in PSCs is also considered to be suitable for the fabrication of flexbile perovskite solar cells（FPSCs）.FPSCs can be mass produced by the existing process like doctor blading and roll to roll technology and they are an important development direction of PSCs,which is of great sigfinicance for realizing the power supply of flexible electronic devices in some specific scenarios.With the continuous efforts of researchers,the energy conversion efficiency（PCE）of FPSCs has been greatly improved.Although the PCE of more than23%still lag behind their counterpart with rigid substrate,their efficiency is no longer a weak point in their practical applications.Operational stability,mechanical stability and repairability have become more concerned.At this stage,the main constraint to the improvement of the performance of FPSCs is the performance of flexible substrates.Although researchers constantly developing new flexible substrates such as colorless polyimide/ITO,mica/ITO,polymer/graphene and PDMS/PEDOT and achieving good results,their research is still in the laboratory scale,and the existing mainstream products such as PEN/ITO and PET/ITO,are difficult to be replaced in the short run.Therefore,it is still of great significance to develop high-performance FPSCs based on the mature commercial substrates.Compared with PSCs of n-i-p type using high-temperature sintered oxides as electron transport layers,PSCs of p-i-n type can be prepared at low temperature are more suitable for preparation on flexible substrates which are not resistant to high temperature.At the same time,p-i-n type PSCs are also proved to achieve good stability much easier.For qualified flexible solar cells,in addition to high PCE,they should also be mechanically stable to meet the expected application scenarios,so it is essential to improve the flexibility of the active layer itself and endow the active layer with repairable characteristics.Furthermore,for both rigid and flexible solar cells,effictive packaging technology is required in the practical using process to achieve effective blocking of water and oxygen to extend the service life of devices.Based on the considerations above,this paper mainly includes the following aspects:1.Efficient and stable flexible perovskite solar cells enabled by elastic grain boundaries（GBs）encapsulation.The elastic GBs are designed to buffer the stress during the deformation of FPSCs to improve the mechanical stability and crystallinity simultaneously.The elastic GBs are formed by using 2,4,6-Trimethyl-2,4,6-trivinylcyclotrisiloxane（V₃D₃）or polypeptide gel GSSG,the formation of elastic GBs effectively blocks the carrier recombination and ion migration in the grain boundary direction and passivates the grain boundary defects.FPSCs based on this design principle realize the synchronous improvement of energy conversion efficiency and stability.Meanwhile,compared with the reference devices of poor mechanical stability,the FPSCs modified by elastic GBs demonstrate dramatic improvement on mechanical stability.The FPSCs modified by V₃D₃ insitu crosslinking strategy achieve a more remarkable mechanical stability performance,73%of the initial PCE is retained after10000 times of bending test under a small bending radius of 1.5 mm,which means the practicality of FPSCs is greatly improved.2.Efficient and repairable FPSCs based on low temperature repairable functional polymer additives.With the development of component engineering and the improvement of device structure,the main challenge faced by FPSCs in practical application is no longer the improvement of PCE,but the improvement of mechanical performance and service life.It is of great significance to realize the repairable property of FPSCs after stress damage to extend their service life and improve their mechanical stability.In this chapter,based on the comprehensive design consideration of passivation engineering and low-temperature self-healing,specific functional polymer materials are designed as additive.The amino,carbonyl and other groups interigated in the additives can produce supramolecular interaction with perovskite to passivation defects,can significantly improve the quality of perovskite films and consequently improve the photovoltaic performance of PSCs.Meanwhile,the inherent supramolecules interaction in these functional polymer materials endow the materials with the characteristics of self-healing at low temperatures,and repair themselves and the morphology of perovskite films through the interaction with perovskite after stress damage,which has a positive effect for the performance recovery of FPSCs after stress damage.3.Bio-based polymer with high moisture and oxygen blocking performance for nondestructive packing of PSCs.For any type of photovoltaic devices,effective packaging is an indispensable and important part in their practical usage.The blocking of moisture and oxygen by packaging materials can guarantee the stable operation of solar cells and improve their service life greatly.The traditional packaging technology usually uses UV curable adhesive in small scale,and EVA vacuum hot pressing process is used for the packaging of large area modules.However,previous studies have shown that such packaging methods should avoid direct contact between the packaging materials and the effective area of PSCs as much as possible,otherwise,due to its high reactivity and the relatively active chemical properties of perovskite,it will generate negative impact on PSCs during the packaging process.It is worth noting that although the number of newly installed photovoltaic units in China continues to rise,our country has not fully mastered the preparation technology of photovoltaic grade EVA packaging film with high vinyl acetate content and POE yet.Such packaging film has long been dependent on imports.At the same time,the monomer production of EVA and POE materials depends on petrochemical technology,which does not conform to the concept of sustainable development and green development to some extent.In this chapter,inert bio-based polymer materials with more environment-friendly sources are used as packaging materials.While achieving high moisture and oxygen barrier performance,the rigid and flexible perovskite solar cells can be well packaged by BPEE without damage under low temperature and low pressure through the strong non covalent interaction between the material itself and the substrate.