Boosting efficiency and stability of 2D alternating cation perovskite solar cells via rational surface-modification: Marked passivation efficacy of anion

Two-dimensional (2D) alternating cation (ACI) perovskite surface defects, especially dominant iodine vacancies (VI) and undercoordinated Pb2+, limit the performance of perovskite solar cells (PVSCs). To address the issue, 1-butyl-3-methylimidazolium trifluoro-methane-sulfonate (BMIMOTF) and its iodide counterpart (BMIMI) are utilized to modify the perovskite surface respectively. We find that BMIMI can change the perovskite surface, whereas BMIMOTF shows a nondestructive and more effective defect passivation, giving significantly reduced defect density and suppressed charge-carrier nonradiative recombination. This mainly attributes to the marked passivation efficacy of OTF- anion on VI and under coordinated Pb2+, rather than BMIMI+ cation. Benefiting from the rational surface-modification of BMMIMOTF, the films exhibit an optimized energy level alignment, enhanced hydrophobicity and suppressed ion migration. Consequently, the BMIMOTF-modified devices achieve an impressive efficiency of 21.38% with a record open-circuit voltage of 1.195 V, which is among the best efficiencies reported for 2D PVSCs, and display greatly enhanced humidity and thermal stability.& COPY; 2023 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

Automated summary

The surface defects of 2D perovskite play a limiting role in the performance of perovskite solar cells (PVSCs). In this study, a modification strategy using 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIMOTF) was found to effectively reduce defect density and suppress nonradiative recombination. The modified devices achieved a high efficiency of 21.38% and displayed enhanced humidity and thermal stability.