Research On Tin-based Perovskite Solar Cells Performance Augmented By Amino Small Molecules

Owing to their outstanding optoelectronic characteristics,such as minimal toxicity,high carrier mobility,diminished exciton binding energy,and appropriated bandgap,tin-based perovskite materials have garnered considerable interest in recent years as potential replacements for lead-based perovskites within the realm of solar cells,researchers have devoted considerable attention to this field.Drawing inspiration from the advancements in lead-based perovskite and organic photovoltaic cells,tin-based perovskite solar cells（TPSCs）have experienced rapid development over the past decade.Currently,TPSCs have achieved a photoelectric conversion efficiency（PCE）of 14.8%,closely approaching the highest PCE of 26.0%for lead-based perovskite solar cells.Nonetheless,due to the rapid crystallization and the extreme susceptibility to oxidation of Sn²⁺in tin-based perovskite,problems such as subpar film quality,p-type self-doping,and severe ion migration arise,ultimately manifesting in devices with diminished PCE and inadequate stability.This study aims to address the suboptimal performance and stability of tin-based perovskite solar cells,which stem from the inferior crystal quality of tin-based perovskite and the facile oxidation of Sn²⁺.To this end,we have selected several small amino molecules as dopants and embarked on the following lines of research:（1）Employing dopamine hydrochloride（DACl）as a dopant and incorporating it into the precursor solution of tin-based perovskite enables the dual regulation of perovskite crystallization and Sn²⁺oxidation,substantiating that the introduction of DACl constitutes an effective strategy for enhancing device performance.DACl fulfills the following three functions:（1）optimizing the crystallization process by diminishing the supersaturation concentration of perovskite in the precursor solution and serving as a pre-nucleation site;（2）with the function of its reducing phenol group and engendering weak acidity in the precursor solution to inhibit the oxidation of Sn²⁺,while the intramolecularπ-conjugated structure fosters carrier transport;（3）the amino and chloride ions in DACl can associate with uncoordinated Sn²⁺and iodide ion vacancies within the perovskite lattice,thereby reducing the defect density of states.Ultimately,the optimized lead-free perovskite(FA_0.75MA_0.25Sn I₃)solar cells,with the addition of 1 mol%DACl,attained a PCE approaching 11%,while the fill factor（FF）experienced a substantial increase from 53.2%to 68.9%.Furthermore,in comparison to the reference device,the unencapsulated cell exhibited superior stability under N₂ambient and air conditions:after aging for 600 hours in an N₂ glove box,it retained over 80%of its initial PCE,and following 100 minutes of exposure to an air environment,it remained above 60%of its initial PCE.（2）Incorporating semicarbazide hydrochloride（SEM-HCl）as a dopant into the precursor solution of tin-based perovskite,through the coordination between the O=C-N functional group and the Sn²⁺in perovskite,substantially enhances the film’s morphology and crystallinity,inhibits Sn²⁺oxidation,and passivates the trap state.Ultimately,the FA_0.75MA_0.25Sn I₃ solar cells,prepared with the addition of 3 mol%SEM-HCl,achieved the PCE of 10.9%.Moreover,the unencapsulated device exhibited improved stability in both N₂ and illuminated environments,with negligible decline in PCE after 100 hours of continuous illumination.This study employs Kelvin probe force microscope（KPFM）to characterize the change in surface potential of the perovskite film before and after the addition of SEM-HCl.The results indicate that SEM-HCl effectively suppresses the generation of Sn vacancies in the perovskite film,thereby reducing the adsorption of oxygen molecules on the film.This optimization serves to inhibit the combination of photogenerated carriers and adsorbed oxygen molecules in running condition,consequently preventing the formation of superoxide.This approach contributes to the development of high-performance,light-stable tin-based perovskite solar cells.（3）Employing fluorinated phenylhydrazine hydrochloride（F-PhCl）as a dopant within the tin-based perovskite precursor solution,effectively suppresses Sn²⁺oxidation through the reducing hydrazine group in F-PhCl,and Fourier transform infrared spectroscopy（FTIR）substantiates that the F ions can form hydrogen bonds with organic amine ions in the tin-based perovskite,thereby enhancing the film’s resistance to moisture and heat.Consequently,the performance of the device and its stability under humid and heated conditions are significantly improved.Ultimately,the tin-based perovskite solar cell with the addition of 1 mol%F-PhCl,attains the PCE of 10.8%.Simultaneously,it is noteworthy that the unencapsulated device retains 68%of its initial efficiency when exposed to an N₂ environment at 70°C for 8 hours,and maintains 73%of the initial efficiency when placed in an air environment for 160 minutes.This demonstrates a marked enhancement in moisture and heat stability compared to the reference device.