Abstract
In this paper we report on the influence of light and oxygen on the stability of CH3 NH3 PbI3 perovskite-based photoactive layers. When exposed to both light and dry air the mp-Al2 O3 /CH3 NH3 PbI3 photoactive layers rapidly decompose yielding methylamine, PbI2 , and I2 as products. We show that this degradation is initiated by the reaction of superoxide (O2 (-) ) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O2 (-) species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O2 (-) generation is significantly reduced when the mp-Al2 O3 film is replaced with an mp-TiO2 electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH3 NH3 PbI3 to a species without acid protons could improve tolerance to oxygen and enhance stability.
Highlights
Over the last few years, organic lead halide perovskites have aroused enormous interest with respect to their application in low-cost, solution-processable photovoltaics
In our previous work we employed transient absorption spectroscopy to monitor the yield of long-lived charge separation in mesoporous TiO2/CH3NH3PbI3/spiro-OMeTAD and Al2O3/CH3NH3PbI3/spiro-OMeTAD photoactive layers before and after exposure to light and oxygen
We show that the combined action of light and molecular oxygen on CH3NH3PbI3 photoactive layers results in the decomposition of the perovskite leading to the formation of PbI2, I2 and methylamine
Summary
Over the last few years, organic lead halide perovskites have aroused enormous interest with respect to their application in low-cost, solution-processable photovoltaics. This compound is known to show a characteristic increase in emission at 610 nm upon exposure to the superoxide radical anion.[11] CH3NH3PbI3 films were fabricated onto two glass substrates coated either with mp-TiO2 or mp-Al2O3.
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