Research On Tin-based Low-dimensional Dion-jacobson Perovskite Solar Cells

Nowadays,the rapid development of science and technology is consuming a large amount of fossil reserves on earth,and in order to meet our growing demand for energy,the spread use of sustainable,clean and renewable sources,such as perovskite solar cells（PSC）whose power conversion efficiency（PCE）of organic-inorganic hybrid ones has reached 25.7%,becomes extremely significant.The highly toxic lead element,which is currently widely used in perovskite solar cells,tends to cause great damage to the human body and our living environment,while tin（Sn）becomes the best choice to replace the toxic Pb for its non-toxic property,similar electronic structure characteristics to lead（Pb）,narrower band gap（Eg）and higher electron and hole mobility.However,the most unignorable flaw of tin perovskite is its poor stability.When tin is oxidized,self-p-doping is induced in perovskite films,resulting in reduced semiconductor properties and poor film morphology,eventually severely impairing the efficiency of PSCs.In order to ameliorate the stability of tin perovskite films,low-dimensional perovskites have attracted a lot of attention and exploration.In those perovskites,bulky organic cationic spacers are intercalated into the lattice of 3D perovskites,and their hydrophobic property and higher formation energy can alleviate water-oxygen erosion and form a more stable structure.Therefore,this paper combines the above two fields to explore high-stability low-dimensional tin-based perovskite solar cells from the following three aspects.Firstly,an aromatic material 1,5-naphthalenediamine（NDA）was selected to be the organic spacer for low-dimensional perovskites.The benzene ring withπ-conjugation structure is beneficial for charge transport when it is used as the organic spacer for low-dimensional perovskites.Meanwhile,under ideal conditions,the rigid structure will also improve the stability of perovskite solar cells.The iodonium salt NDAI₂ was successfully synthesized by protonation procedure and was applied to the perovskite films and solar cells.According to the experiment results,NDAI₂ can indeed form a low-dimensional structure,but its low solubility and high structural rigidity have a great negative impact on the film formation process,resuling in the poor film morphology.Adjustments of solvent ratio,spin coating speed and annealing temperature as well as addition of additives were invalid in changing this situation,thus the power conversion efficiency and stability of the device were greatly reduced.Secondly,considering the negative effects of bulky and rigid organic spacer on perovskite films,3-（aminoethyl）-pyridine（3AEP）,an aromatic material containing flexible alkyl chains,was selected to be the low-dimensional organic spacer.We synthesized 3AEP into 3AEPI₂ and used it to prepare low-dimensional tin-based perovskite films and solar cells.The formation of low-dimensional structure was confirmed.After adjusting the parameters such as concentration,spin coating speed and annealing temperature,the highest PCE obtained was 2.81%with the short-circuit density,open-circuit voltage and the fill factor（FF）of 8.75 m A/cm²,0.47 V and68.23%.The lower current density is due to the more grain boundaries induced by the small grains,which adversely affects charge transport.However,the formed low-dimensional structure greatly improves the device stability.After placing the unencapsulated device in a N₂ glove box for more than 1200 h,the device was still able to maintain more than 85%of its initial efficiency,confirming the dramatic improvement in device stability with our spacer materials.Thirdly,a new material,4-（aminoethyl）-pyridine（4AEP）,which has a similar structure to3AEP,was selected to study the effect of different substituent positions on the photoelectric properties of perovskite films.The results show that films based on para-structure 4AEP has larger interlayer distance and wider band gap than 3AEP ones.In addition,the 4AEP device achieves the highest efficiency of 2.42%,with a short-circuit density of 8.73 m A/cm²,an open-circuit voltage of 0.46 V,and a fill factor（FF）of 60.62%.The reason why the meta structure is superior to the para structure is that its smaller band gap and interlayer distance improve the optoelectronic properties of the device.The unencapsulated device was able to maintain 80%of its initial efficiency after storage in a nitrogen glove box for more than 1200 h,indicating that both para-structure and meta-structure AEP can contribute to the formation of stable low-dimensional tin-based perovskites and improve the stability of the solar cells.In conclusion,in order to solve the stability issues in tin-based perovskites,several aromatic materials that can be used as low-dimensional perovskite spacers are studied to improve the stability of PSCs.The results in this thesis provide some valuable references for further solving the stability problems existing in the field of tin-based perovskites.