Abstract
Perovskite solar cells have received worldwide interests due to swiftly improved efficiency but the poor stability of the perovskite component hampers the device fabrication under normal condition. Herein, we develop a reliable nonstoichiometric acid–base reaction route to stable perovskite films by intermediate chemistry and technology. Perovskite thin-film prepared by nonstoichiometric acid–base reaction route is stable for two months with negligible PbI2-impurity under ∼65% humidity, whereas other perovskites prepared by traditional methods degrade distinctly after 2 weeks. Route optimization involves the reaction of PbI2 with excess HI to generate HPbI3, which subsequently undergoes reaction with excess CH3NH2 to deliver CH3NH3PbI3 thin films. High quality of intermediate HPbI3 and CH3NH2 abundance are two important factors to stable CH3NH3PbI3 perovskite. Excess volatile acid/base not only affords full conversion in nonstoichiometric acid–base reaction route but also permits its facile removal for stoichiometric purification, resulting in average efficiency of 16.1% in forward/reverse scans.
Highlights
Perovskite solar cells have received worldwide interests due to swiftly improved efficiency but the poor stability of the perovskite component hampers the device fabrication under normal condition
The degradation kinetics had been studied to some extent using thermal gravity analysis (TGA)22 and ultrafast spectroscopy23, which revealed some possible routes, but the degradation process related to transition states and intermediate products is not well-resolved
On the basis of this, we have developed an alternative two-step nonstoichiometric acid–base reaction route (NABR) for the synthesis of moisture-resistive perovskite, that is the production of starting HPbI3 using excess HI to react with PbI2, followed by perovskite conversion from HPbI3 using excess CH3NH2
Summary
Perovskite solar cells have received worldwide interests due to swiftly improved efficiency but the poor stability of the perovskite component hampers the device fabrication under normal condition. Perovskite thin-film prepared by nonstoichiometric acid–base reaction route is stable for two months with negligible PbI2-impurity under B65% humidity, whereas other perovskites prepared by traditional methods degrade distinctly after 2 weeks. CH3NH3I was very thermally stable even when the temperature increased to 150 °C (refs 22,25), but the perovskites quickly decayed to PbI2 in association with CH3NH2/HI release at 80–150 °C after 24 h, which meant the decomposition kinetic pathways were different from each other26 This degradation kinetics of perovskite requires a closer examination to address these stability issues, and an alternative strategy is expected for enhancement of perovskite stability while keeping its high performance. We have demonstrated that the CH3NH3PbI3 perovskite thin-film remained highly stable in B65% humidity for up to 2 months with negligible PbI2-impurity, whereas other perovskites prepared by traditional one-step or two-step methods degrade distinctly after 2 weeks.
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