Study On Performance Of SnO₂-based Perovskite Solar Cells Regulated By Functional Small Molecules

As one of the most promising new generation photovoltaic devices,perovskite solar cells（PSCs）have developed rapidly with unprecedented performance achievements in just decade.However,intrinsically unstable perovskites tend to form charged ion defects（with lower formation energy）during solution processing,which induces carrier recombination.Water,continuous light and heat further induce ion diffusion and migration,eventually lead to irreparable degradation of PSCs,thereby shortening the lifetime and affecting performance.Notabelly,most PSCs are accomplished in glove box to ensure high performance of PSCs,which inevitably increases cost and hinders commercial large-scale production.Fabricating PSCs with high performance in an uncontrolled air environment remains challenging,including tuning grain growth and fabricating perovskite film with passivated surface and grain boundar y.Based on additive engineering and interface engineering,this study proposes diverse and efficient small molecules to regulate perovskite grain growth,passivate defects,and explore the influence of molecular configuration on the regulation effect.Furthermore,Sn O₂,perovskite and their interface are simultaneously optimized by thiocyanate to facilitate the separation and transport of charge carriers.This study is devoted to achieve the goal of reducing the defects and suppressing ion migration,preparing PSCs with high performance and stability in air environment.In view of vacancy defects easily formed in the solution spin coating process,terephthalic acid（PTA）with carboxylic acid groups（-COOH）is introduced to form Lewis acid-base coordination to regulate the growth of perovskite crystals,passivate vacancy defects and suppress carrier recombination.Fluorescence lifetime of the PTA-modified perovskite film is extended from 102.21 ns to 153.50ns,indicating that the modification of PTA effectively reduced defects and alleviated carrier recombination.In the atmosphere,PTA-modified high-quality perovskite films facilitate PSCs with enhanced performance of 18.22%.PTA-modified perovskite demonstrates the validity of coordination strategy.The influence of molecular configuration（changes in the relative position of-COOH）on the modification effect is explored by PTA with opposite-COOH,isophthalic acid（IHA）with interphase-COOH and phthalic acid（Phthalic acid,PHA）with adjacent-COOH.Density functional theory calculations show that the PHA-Pb I₂ system has a lower binding energy.Two adjacent-COOH in PHA tends to provide concentrated electron donors and form dual coordination with the uncoordinated Pb²⁺,significantly augments the modification effect.Furthermore,the dual coordination induces unique protrusion morphologies on perovskite films,providing green channels to facilitate charge transport and increasing the photogenerated current density of PSCs from 21.60 m A cm^-2 to 22.80 m A cm^-2.In addition to carboxyl groups,functional small molecules with amino groups also provide better coordination with perovskites.Therefore,regulation of perovskites on basic of covalent bonding strategies still remains much room for development.By introducing 5-amino-1H-tetrazole（5-ATZ）,where-NH₂,-NH tend to interact with the Pb and I in perovskite,anchoring defects and preventing ions migration.Therefore,the fluorescence lifetime of 5-ATZ-modified perovskite film is extended from 137.5 ns to 216.4 ns.Furthermore,the extensiveπelectron delocalization around the tetrazole conjugated ring in 5-ATZ significantly facilitates charge transfer and alleviates the interfacial charge accumulation.Therefore,the 5-ATZ-modified PSCs provided enhanced open circuit voltage and reduced hysteresis factor.In addition,unencapsulated 5-ATZ-modified PSCs exhibits improved stability,maintain 90.85±2.53%of the initial performance after 1464 h storage in air atmosphere and 86.00±1.83%of initial performance after heating at 100°C for 20 h.Vacancy-related defects are successfully passivated and suppressed by multifunctional small molecules coordination strategies,manifested in the enhanced performance and stability of PSCs.However,in order to achieve higher performance PSCs,attention should also be focused on electron transport layer（ETL）and interface of ETL/perovskite.Poor charge extraction and transport at ETL/perovskite interface will lead to PSCs with small fill factors.NH₄SCN is introduced,its interaction with Sn O₂ could stabilize Sn O₂ micelles.NH₄SCN featured volatility and freeness can be used as a mobile medium,driving the movement of ions during Sn O₂ film formation to regulate and promote crystallization,forming dense Sn O₂"cluster-like crystal".Simultaneously,the conduction band of Sn O₂ is regulated to deeper energy level,forming a larger conduction band energy level difference with perovskite to drive more efficient charge extraction and transport.In addition,the interaction between thiocyanate and perovskite precursor solution,and"cluster-like crystal"morphology,synergistically provide a good growth template for the deposition of perovskite films.Multifunctional optimization strategy provided by NH₄SCN enables PSCs with 20.38%champion performance and fill factor generally exceeding 80%,steady-state output performance as high as 19.88%.