Development And Applications Of Dual Passivation Strategy In Perovskite Solar Cells

In recent years,organic-inorganic halide perovskites solar cells（PSCs）have been the research focus in the field of thin-film photovoltaics,due to their high carrier migration rate,tunable energy levels,long carrier diffusion length and availability for solution processing.Since high-efficiency PSCs are generally fabricated by low-temperature solution processing,this inevitably results in a large number of structural defects during the deposition of polycrystalline perovskite films.The presence of defects induces severe non-radiative recombination and ion migration,therefore damaging the performance of PSCs.Meanwhile,the external factors including moisture,oxygen,light,and high temperature can attack the internal structure of perovskite via film defects and accelerate the perovskite decomposition,thus affecting the long-term stability of PSCs.Defect passivation by post-treatment is a simple but efficient method of fixing structural defects in perovskites and enhanceing the performance and stability of PSCs.However,the conventional passivation methods only fix defects through one-step passivation process,which is less efficient to make use of the full potential of PSCs.Therefore,a new passivation method called dual passivation strategy has been proposed in this paper.In this novel strategy,the passivation component is able to achieve a dual passivation process under specific environment conditions after the primary passivation process,to further repair the structural defects of perovskites and construct highly efficient and stable PSCs.The details of the study are as follows.（1）A temperature-controlled dual passivation strategy based on azo compounds for construction of high-performance PSCsA temperature-controlled dual passivation strategy is developed by introducing a series of azo compounds for fabricating efficient and stable PSCs.These azo molecules contain carbonyl and/or cyano groups in this molecular structure,which interact with the perovskite surface to complete the primary passivation process.Following the thermal decomposition of the azo compound,the reaction occurs during subsequent annealing and diffuses through the grain boundaries（GBs）to the interior of the perovskite to passivate the defects in the bulk of the perovskite,thus achieving dual passivation.The dual passivation strategy,constructed by the two-step passivation process,eventually achieved a device efficiency of 19.69%PCE,far higher than the standard device（16.92%）.Furthermore,the thermal and long-term stability of the PSCs is significantly improved due to the enhancement of the perovskite film quality.After 800 hours of heating in a N₂ atmosphere,the azo-passivated PSCs retain more than 50%of the initial PCE,while the standard devices retain less than 20%of the initial PCE;meanwhile,the AIBME-passivated PSCs lost only 10%of the initial PCE after 3000 hours.（2）A light-controlled dual passivation strategy based on photosensitive molecules for construction of high-performance PSCs.A light-controlled dual defect passivation strategy based on a series of photosensitiser molecules is developed.In the primary passivation process,the carbonyl group on photosensitiser molecules effectively passivate the defects in perovskite surface.The photosensitiser molecule decomposes after UV treatment and then diffuses through the grain boundaries（GBs）into the interior of the perovskite to passivate the defects in the bulk of the perovskite,thus dual passivation is accomplished.After treatment by a series of photosensitiser molecules,the crystallinity of the perovskite is significantly enhanced,the PL emission intensity is greatly improved and the TRPL decay lifetime increases from93.23 ns for standard perovskite films to 220.56 ns（HDE）,158.98 ns（BIE）and 247.33 ns（DPE）.Thus,the device exhibits an optimized PCE of 19.64%.Furthermore,the light stability of PSCs is significantly enhanced as the photosensitiser molecules are continuously decomposed and diffused under light.Under AM 1.5G sunlight,the photosensitized devices keep more than 60%of the initial PCE after 900 h,while the standard devices maintain only 20%of the initial value under identical condition.（3）A dual passivation strategy based on acrylamide（AM）self-polymerization for the construction of high-performance PSCs.A dual defect passivation strategy for PSCs is achieved by introducing acrylamide（AM）molecules.The primary passivation process is accomplished by the AM molecules deposited on the perovskite surface,which form coordination bonds with defects through the amine and carbonyl groups in the molecular structure.Since AM can be self-polymerization under a certain thermal-annealing condition（82～86°C）,the subsequent annealing treatment up to 100°C enables the polymerization of AM on upper surface of perovskite film,thus dual passivation is accomplished.After AM treatment,the pores on the surface of perovskite are reduced and the crystallinity is significantly enhanced.Also,the PL emission intensity of the perovskite films is greatly improved and the TRPL decay lifetime increases from 52.89 ns to 78.83 ns.Therefore,the PCE of AM-treated device exhibits significant enhancement from 17.23%to 19.12%.