Optimization Of Perovskite Light-absorbing Layer In Planar Perovskite Solar Cells

Planar perovskite solar cells（PSCs）have become the most promising new-generation solar cells due to their excellent photovoltaic performance,simple preparation process and low cost.However,the development of planar PSCs faces two major challenges:charge loss and device degradation.To solve these two problems,it’s significant to reduce the defects inside perovskite film or at interfaces and enhance the stability of perovskite film.From the perspective of optimizing the perovskite light-absorbing layer,we have conducted a series of strategies to improve the photoelectric properties and stability of perovskite film,including adjusting the crystallization process of perovskite film,facilitating the separation of photogenerated carriers inside perovskite film and passivating the defects inside perovskite film or at interfaces.The main contents of this thesis are as follows:To adjust the crystallization process of perovskite film,graphene quantum dot（GQD）is introduced into the CH₃NH₃PbI₃（MAPbI₃）perovskite precursor to adjust the crystallization process of perovskite film.GQD can provide heterogeneous nucleation sites for perovskite.Hence,GQD modified perovskite films exhibit significantly increased grain size and reduced surface defects.Meanwhile,GQD can also be utilized as the electron collector and transmission bridge,thus realizing the effective separation of photogenerated electrons and holes inside perovskite film.To facilitate the separation of photogenerated carriers inside perovskite film,chlorobenzene containing dispersed graphdiyne（GDY）is utilized as the anti-solvent to introduce GDY nanosheets into the upper part of the MAPbI₃ perovskite film.GDY on the upper part of perovskite film plays an essential role in collecting and transporting holes,further realizing the automatic separation of photogenerated electrons and holes inside perovskite film.In the meanwhile,a Schottky barrier is formed at the interface between GDY and perovskite,ensuring the unidirectional transport of holes from perovskite to GDY.To passivate the defects of perovskite film,room-temperature synthesized CsPbBr₃ nanocrystal（CN）is exploited as the bilateral interface modifier of MAPbI₃perovskite film.The CN located at the surface of SnO₂ film can be utilized as the seed crystal to facilitate the seed growth of perovskite.Moreover,CN effectively reduces the defects and energy barriers at the interface between SnO₂ and perovskite.CN surface modification can increase the difference in Fermi levels between the surface and the bottom of perovskite film,thus enhancing the built-in electric field of PSCs.This is advantageous to the separation and oriented transport of photogenerated electrons and holes inside perovskite film.To improve the inherent stability of perovskite film,bulky organic molecule C₄H₉NH₃（BA）is introduced into the perovskite precursor solution.The growth orientation of two-dimensional（2D）perovskite（BA）₂（MA）₃Pb₄I₁₃ is adjusted through the binary solvent engineering of N,N-dimethylformamide（DMF）and dimethyl sulfoxide（DMSO）.In the DMF/DMSO binary solvent,the formation of intermediate adducts will delay the crystallization process of 2D perovskite,so 3D perovskite cap layer can be utilized as the seed crystal to facilitate the vertical growth of 2D perovskite.Through the above strategies,we not only successfully prepare planar PSCs with high power-conversion efficiency and excellent stability,but also analyze the mechanism of enhanced photovoltaic performance and stability.Therefore,this thesis provides ideas for the development of high-efficiency and long-term stable planar perovskite solar cells.