Research On Performance And Stability Of Perovskite Solar Cells With Sulfur-containing Additives

Organic-inorganic metal halide perovskite was selected as the photoactive layer due to their high carrier mobility,long-range exciton diffusion lengths,high absorption coefficients and adjustable optical bandgap.The power conversion efficiency(PCE)of perovskite solar cells(PSCs)has boosted from 3.8%to over 25.5%in the past several years.However,the stability issue of PSCs remains one of the major challenges to be solved before their practical application.Significant efforts have been devoted including compositional engineering,encapsulation,interface tuning,and additive engineering to address this challenge.Additive engineering is the most commonly used method to passivate perovskite defects and improve device stability.For example,common multifunctional additive materials include molecules containing specific functional group ions,lewis acid or basic molecules,wide band gap materials,etc.,can passivate perovskite defects,form an interface protection layer,and optimize energy level structure.In this paper,we take Cs_0.05(FA_0.85MA_0.15)_0.95Pb(I_0.85Br_0.15)₃ perovskite as the research object,and introduce three different sulfur additives to improve the performance and stability of perovskite film and device.First of all,the quality of the perovskite film can be improved,including crystal size,crystallinity by introducing sulfamic acid(SA)additives due to the interaction of sulfonate ions with lead ions(Pb²⁺)in the precursor solution.In addition,the improvement of these properties of SA doped perovskite films can be attributed to the strong coordination effect between the sulfonate ion in SA and the under-coordinated Pb²⁺in the perovskite and the hydrogen bond between-NH₂ and halogen ions which can effectively passivate both positive and negative charged defects.Compared with the pristine device,the PCE of the SA doped device increased from 17.13%to 18.41%and the unencapsulated device can retain 74.5%of its initial efficiency under ambient condition at 60°C after 30 days.Considering that the molecular structure has an important influence on the role of additives,after that,we continue to use additives containing sulfonic acid groups and choose a?-conjugated sulfur-containing additive molecule-4-aminobenzenesulfonic acid(4-ABSA)to further improve the quality of the perovskite film and the performance of device.This?-conjugated sulfur-containing additive molecule contains an amine group(-NH₂),a sulfonic group(-SOOOH),and a benzene ring.It was found that the functional groups of 4-ABSA can construct a compact and smooth perovskite film,but also are capable of passivating both negative and positive charged defects derived from under-coordinated lead and halogen ions.More importantly the?-conjugated benzene ring in4-ABSA could induce preferred crystal orientation and stable the coordination effect between4-ABSA and perovskite grains.As a result,the inverted PSCs incorporated with 4-ABSA additives demonstrated an improved PCE from 18.25%to 20.32%.Furthermore,such 4-ABSA passivation agent also enhances the stability of devices with heat stress and light illumination,respectively.For example,After aging for 27 days at a relative humidity of 40%and a temperature of 60°C,the4-ABSA device exhibited better stability and still maintains 83.5%of its initial efficiency and showed better stability.Finally,we studied the effect of a sulfur-containing multidentate molecular additive—2-mercaptonicotinic acid(2-MNA)on the performance of perovskite films and devices.This molecular contains pyridine and sulfhydryl groups that can simultaneously interact with Pb²⁺in the perovskite.This synergistic effect can enhance the anchoring strength to defects of perovskite,thereby improving passivation efficiency and stability.Compared with the pristine perovskite film and niacin(NA)only containing pyridine doped perovskite film,the moisture resistance of the2-MNA doped film was significantly improved,and after aging under light or heat,the film showed constant PL intensity and peak position.Preliminary research shows that the PCE of the device passivated by 2-MNA was increased to 19.94%.The 2-MNA PSC could still maintain 71%of its initial efficiency exposed at 60°C in air(relative humidity 40%)after 30 days.Through the above three studies on sulfur-containing additives,we hope to provide some valuable improvement ideas for additive engineering to improve the efficiency and long-term stability of perovskite solar cells.