3 research outputs found
Degradation by Exposure of Coevaporated CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Thin Films
Degradation
of coevaporated CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> thin films
were investigated with X-ray photoelectron spectroscopy
and X-ray diffraction as the films were subjected to exposure of oxygen,
low pressure atmospheric air, atmospheric air, or H<sub>2</sub>O.
The coevaporated thin films have consistent stoichiometry and crystallinity
suitable for detailed surface analysis. The results indicate that
CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> is not sensitive to oxygen.
Even after 10<sup>13</sup> Langmuir (L, one L equals 10<sup>–6</sup> Torr s) oxygen exposure, no O atoms could be found on the surface.
The film is not sensitive to dry air as well. A reaction threshold
of about 2 × 10<sup>10</sup> L is found for H<sub>2</sub>O exposure,
below which no CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> degradation
takes place, and the H<sub>2</sub>O acts as an n-dopant. Above the
threshold, the film begins to decompose, and the amount of N and I
decrease quickly, leaving the surface with PbI<sub>2</sub>, hydrocarbon
complex, and O contamination
Light-Induced Degradation of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Hybrid Perovskite Thin Film
The
stability of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> was
investigated by observing the degradation in a coevaporated film irradiated
by a blue laser in ultrahigh vacuum. X-ray photoelectron spectroscopy
(XPS) and scanning electron microscopy (SEM) were employed to investigate
the effects of irradiation on the surface. The core levels of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> were observed to shift toward
a higher binding energy (BE) during the irradiation, suggesting that
the surface became more n-type. A new metallic Pb component in the
XPS spectrum appeared after 120 min of irradiation, indicating that
the film had started to decompose. The decomposition saturated after
about 480 min of irradiation when the ratio of metallic Pb to total
Pb was about 33%. Furthermore, the film was no longer continuous after
irradiation, as the elements gold and oxygen from the substrate were
detected by XPS. SEM images also show a roughened surface after irradiation.
The results strongly indicate that CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> is sensitive to the laser irradiation and that the light
induced decomposition is a self-limiting process
Air-Induced High-Quality CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> Thin Film for Efficient Planar Heterojunction Perovskite Solar Cells
Efficient
planar heterojunction perovskite solar cells (PHJ–PSCs)
with a structure of ITO/PEDOT:PSS/CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>/PCBM/Al were fabricated using air-induced high-quality CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> perovskite thin films, in which
the air-inducing process was controlled with a humidity of ∼40%.
The air exposure of CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> thin
films could dramatically improve their properties with large grains
and smooth surface, as well as uniform morphology, resulting in an
impressive enhancement in carrier lifetime. The ultraviolet photoelectron
spectroscopy and X-ray photoelectron spectroscopy results proved that
the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> film was <i>n</i>-doped by the absorption of H<sub>2</sub>O on the surface but was
very stable without obvious degradation for 10 days’ exposure
in air. The power conversion efficiency (PCE) of PHJ–PSCs with
an air exposure process showed a significant increase up to 16.21%
as compared to reference PHJ–PSCs with a PCE of 12.02%. The
research work demonstrated that an air-exposure process with a suitable
humidity could produce high-quality perovskite thin film for efficient
PHJ–PSCs, which may pave a boulevard for fabricating high-efficiency
PHJ–PSCs in atmospheric environment