Research On Interface,Defect Modulation And Device Performance Of Perovskite Solar Cells

Organic metal halide perovskite solar cells（PSCs）have generated extensive research interest around the world due to their low-cost solution process and significantly boosted power conversion efficiency（PCE）,with the certified PCE of single-junction PSCs reaching 26.1%so far.Compared with crystalline silicon cells,PSCs have more advantages in terms of photovoltaic efficiency,raw material price,production cycle and levelized cost of energy（LCOE）.PSCs are expected to become a disruptive technology for revolutionizing the photovoltaic industry and contributing to the implementation of Chinese“dual-carbon”strategy.However,the current PCE of PSCs is still below the theoretical Shockley-Queisser limit efficiency and the long-term stability of devices is far from commercialization,which is mainly attributed to the following fact:（i）the generation of substantial deleterious defects during the deposition of electron transport layer-perovskite layer-hole transport layer to form the interface,which may cause severe interfacial nonradiative recombination and aggravate water/oxygen intrusion in the external environment;（ii）charged defects-induced ion migration under the electric field effect leads to unfavorable energy band bending and thus affects the extraction and transport of carriers at the interface;（iii）polycrystalline perovskite films have poor crystallinity,irregular grain orientation and high density of grain boundaries.To improve the efficiency and stability of PSCs,we choose Cs FAMA-based perovskite as the research perovskite component.Aiming at passivating surface/grain boundary defects,enhancing the crystalline quality of perovskite films as well as improving the interfacial contact and alignment of energy levels between perovskite and charge transport layer,we successfully realize the fabrication of high-efficiency and stable PSC devices by virtue of interfacial modification,bulk phase doping,and ambient storage.The detailed research is as follows:（1）A practical buried interfacial modification strategy was developed by introducing a multifunctional organic small molecule histidine（His）into the Sn O₂/perovskite interface.Multiple functional groups in His（including carboxy oxygen,imidazole ring and amino group,etc.）can cross-link Sn O₂and perovskite layers through coordination and electrostatic interactions,which not only effectively passivates interfacial defects and reduces interfacial nonradiative recombination losses but also improves the Sn O₂/perovskite interfacial contact and promotes the growth of the upper perovskite crystals.In addition,the His modification upshifts the conduction band of Sn O₂,which reduces the interfacial energy barrier to achieve a favorable energy level alignment and thus promoted electrons transport.The His-modified devices with the structure of ITO/Sn O₂/His/Cs_0.15FA_0.75MA_0.1Pb I₃/Spiro-OMe TAD/Ag produces an outstanding PCE of 22.91%（from 20.13%）and superior humidity stability and thermal stability.（2）A polyfluorine-substituted interfacial modification material,3,5-bis（trifluoromethyl）benzenethiol（35BBT）,was employed to regulate the perovskite/Spiro-OMe TAD interface.Dual interface-modified Ag-PSCs were constructed by combining previous His buried interface modification strategy.35BBT synergistically passivates perovskite top surface/grain boundary defects through two-site anchoring.Specifically,the S atoms in the mercapto group form Pb-S bond with uncoordinated Pb²⁺,and the F atoms of the trifluoromethyl group not only fill the I vacancy defects but also immobilize organic cations such as FA/MA through hydrogen bonding,inhibiting the ion migration.Meanwhile,the 35BBT modification achieves a more favorable interfacial energy band alignment,which facilitates the extraction of interfacial holes.The dual interface-modified PSCs with the architecture of ITO/Sn O₂/His/Cs_0.15FA_0.75MA_0.1Pb I₃/35BBT/Spiro-OMe TAD/Ag yield a superior champion efficiency of 23.86%and a high open-circuit voltage of1.18 V.Furthermore,the long-term stability of the devices is substantially improved due to the excellent moisture and heat resistance of fluoride.The dual interface-modified device still maintains 89.1%of the initial efficiency after aging at 20-30%RH for 2000 h in air.The device retains 86.7%of the original efficiency after aging at 60°C for 500 h in N₂ environment.（3）A bulk phase doping strategy was designed to significantly enhance the perovskite film crystalline quality by introducing a dye intermediate2-anisidine-4-sulfonic acid（2A4SA）into the perovskite precursor solution,which simultaneously achieves perovskite defect passivation and crystalline orientation modulation.The sulfonic acid group in 2A4SA anchors Pb²⁺defects by coordination interaction,the amino and methoxy group fix I^–and organic cations in perovskite by hydrogen bonding,respectively.In addition,2A4SA molecules adhere to the surface of perovskite nuclei during the nucleation and crystallization process of perovskite,which slows down the crystallization rate of perovskite and promotes the growth of perpendicular orientation,and ultimately obtains the high-quality perovskite films with high crystallinity,low defect density,and large grain size.The 2A4SA-doped device achieves a champion efficiency of 23.06%and exhibits better humidity/thermal stability.（4）A simple storage strategy in room temperature environment was developed.Storing the perovskite film in 20-30%RH ambient air for a period,trace moisture in ambient air passivates the surface/grain boundaries of the perovskite film through hydrogen bonding.After prolonging the storage time,moisture further induces grain boundary creep,which promotes the merging of neighbouring grains to realize recrystallization.The perovskite completes“self-healing”,and dense perovskite film with low defect density and high crystallinity was obtained eventually.The film after 10 days of ambient storage achieves the optimal optoelectronic properties,and the best-peforming efficiency of the corresponding PSC is 22.60%,which is significantly higher than the PCE of PSC based on the fresh film（19.75%）.