Enhanced optoelectrical dynamics in ambient-processed CsFAMAPbX3 perovskite solar cells by lithium organic salt doping

The inherent vulnerability of ambient-processed CsFAMAPbX3 perovskite solar cells to humidity has long presented a significant challenge. Incorporating lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) into the CsFAMAPbX3 perovskite lattice markedly improves its processability under ambient conditions with up to 60% relative humidity. Investigation reveals that Li-TFSI facilitates improved bulk structure, morphology, and optoelectronic properties in the resulting perovskite film. Specifically, Li-TFSI dissociation into Li+ and TFSI− ions enhances crystallinity and grain size, leading to faceted grains with a smoother surface topology conducive to interfacial coupling and charge transfer. This passivation effect enables perovskite solar cell fabrication under ambient conditions. Furthermore, Li-TFSI doping reduces the optical band edge, expanding spectral response, and mitigates defect density, all critical factors for ambient processing. Resulting Li-TFSI-doped CsFAMAPbX3 perovskite solar cells (0.1 cm2 active area) exhibit power conversion efficiencies reaching 21.24%, with a short-circuit current density of 25.2 mA/cm2, an open-circuit voltage of 1.11 V, and a fill factor of 75.68%. This represents a 22.3% improvement over pristine devices, which attain maximum efficiencies of approximately 17.37% with corresponding parameters of 23.1 mA/cm2, 1.09 V, and 69.09%, respectively. The champion device maintained 91.8% of its original efficiency following 27 days of storage in an N₂ atmosphere. The integration of Li-TFSI demonstrates substantial promise for ambient-processed CsFAMAPbX3 perovskite solar cells.