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We investigated a silicon nitride (SiN x ) film prepared by catalytic chemical vapor deposition as a gas barrier for further improving stability of mixed-cation-halide perovskite (PVK) Cs0.05FA0.85MA0.1PbI2Br under dark air conditions. The SiN x film can be formed on the PVK capped with carrier transport layers such as 2,2′,7,7′-tetrakis[N,N-di(4-methoxylphenyl)amino]−9,9′-spirobifluorene (Spiro-OMeTAD) and phenyl-C61-butyric-acid-methyl-ester (PCBM)/aluminum-doped-zinc-oxide (AZO) with less degradation in its optical transmittance property and crystal structure. The PVK/Spiro-OMeTAD encapsulated by SiN x exhibits a slower reduction in average carrier lifetime after storage for 330 h at room temperature with ∼65%RH. The PVK/PCBM/AZO covered with SiN x shows a small blue-shift (8–10 nm) in the absorption band-edge of PVK and with less decrease in the transmittance in the long wavelength range for ∼500 h at 85 °C with ∼2%RH. These results demonstrate the effect of SiN x in preventing the degradation of PVK due to the interactions with moisture and oxygen in the air.

We measure the minority carrier lifetime of perovskite films by differential microwave photoconductivity decay (μ-PCD). Clear decay curves can be detected from bare and laminated methylammonium lead iodide (MAPbI3) films by the differential μ-PCD. The degradation of the bare and laminated MAPbI3 films under air exposure at room temperature is clearly observed as the continuous change of the decay curves. The differential μ-PCD can thus be a quick and non-destructive method for the characterization of the electrical quality of perovskite films and modules.

Although the interface between poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and perovskite layers is one of the key factors to determine the open-circuit voltage of inverted perovskite solar cells, this interface remains poorly understood. We investigated the interface by electron spin resonance spectroscopy and found that the PEDOT undergoes dedoping in contact with the perovskite. The holes in PEDOT were reduced by electron transfer from the perovskite. Additional electron transfer occurred upon light irradiation. The electron transfer would be related to lower open-circuit voltages of the inverted structure compared to those of mesoporous and planar structures.