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Insight into Evolution, Processing and Performance of Multi-length-scale Structures in Planar Heterojunction Perovskite Solar Cells.

Huang YC, Tsao CS, Cho YJ, Chen KC, Chiang KM, Hsiao SY, Chen CW, Su CJ, Jeng US, Lin HW - Sci Rep (2015)

Bottom Line: The result is complementary to the currently microscopic study.The GISAXS/GIWAXS measurement provides the comprehensive understanding of concurrent evolution of the film morphology and crystallization correlated to the high performance.The result can provide the insight into formation mechanism and rational synthesis design.

View Article: PubMed Central - PubMed

Affiliation: Institute of Nuclear Energy Research, Longtan, Taoyuan 32546, Taiwan.

ABSTRACT
The structural characterization correlated to the processing control of hierarchical structure of planar heterojunction perovskite layer is still incomplete due to the limitations of conventional microscopy and X-ray diffraction. This present study performed the simultaneously grazing-incidence small-angle scattering and wide-angle scattering (GISAXS/GIWAXS) techniques to quantitatively probe the hierarchical structure of the planar heterojunction perovskite solar cells. The result is complementary to the currently microscopic study. Correlation between the crystallization behavior, crystal orientation, nano- and meso-scale internal structure and surface morphology of perovskite film as functions of various processing control parameters is reported for the first time. The structural transition from the fractal pore network to the surface fractal can be tuned by the chloride percentage. The GISAXS/GIWAXS measurement provides the comprehensive understanding of concurrent evolution of the film morphology and crystallization correlated to the high performance. The result can provide the insight into formation mechanism and rational synthesis design.

No MeSH data available.


GISAXS profiles of the vacuum-deposited CH3NH3PbI3−xClx films prepared at the substrate temperatures of 65, 75 and 85 °C, respectively.
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f1: GISAXS profiles of the vacuum-deposited CH3NH3PbI3−xClx films prepared at the substrate temperatures of 65, 75 and 85 °C, respectively.

Mentions: Figure 1 shows the GISAXS profiles, I(Q), of the vacuum-deposited CH3NH3PbI3−xClx films at the substrate temperatures of 65, 75 and 85 °C, respectively. The GISAXS profiles show the behavior of power-law scattering with the characteristic of surface fractal (I(Q) ∝ Q−α; 3 ≤ α ≤ 4)3334. The exponent α is related to the surface fractal dimension Ds by Ds = 6-α. The surface fractal reveals that film surface has the morphology of self-similarity at different scales starting from nanometers, schematically showing in Fig. 2. The SAXS technique is particularly useful for characterizing fractal aggregation structures/or fractal morphology using the power-law scattering behavior over a wide Q range, which is reported by a large number of papers33343536. The general microscopic tools (SEM, AFM, TEM etc.) are very difficult to identify the fractal morphology. Therefore, the SAXS characterization of the fractal system is complementary to TEM observation. The local morphology observed through TEM may provide a very rough evidence of a fractal object at a certain length scale. The previous study37 reported the fractal morphology in the different perovskite solar cells studied by GISAXS technique, which was correlated to the SEM (for macroscale morphology of large grain) and TEM (nanoscale fractal pore network). This power-law scattering also implies that the internal structure of film comprised of perovskite grains is dense (solid-state) or there is almost no micropore inside the film (or no mesopore between grains). The GISAXS profiles (Fig. 1) shows that the fractal surface morphologies formed at 85 and 65 °C are very similar. In contrast, the surface morphology formed at 75 °C shows a larger scale, evidenced by the power-law scattering at the smaller Q region. This result is consistent with the SEM observation for the films prepared by the same procedure previously reported12. The SEM images showed that all films have the full surface coverage of μm-scale grains. The corresponding AFM measurement shows the Rrms values of ~23 nm. The previous study12 reported that the CH3NH3PbI3−xClx film prepared at 75 °C has much higher PCE (~15%) than those prepared at the other temperatures (6.1% and 4.5% for the subtract temperatures of 65 and 85 °C, respectively). It can be attributed to that the film prepared at 75 °C has the highest CH3NH3PbI3 crystallinity, evidenced by the simple one-dimensional (1D) XRD patterns previously reported12. It seems that the grain morphology is closely related to its crystalline structure and quality.


Insight into Evolution, Processing and Performance of Multi-length-scale Structures in Planar Heterojunction Perovskite Solar Cells.

Huang YC, Tsao CS, Cho YJ, Chen KC, Chiang KM, Hsiao SY, Chen CW, Su CJ, Jeng US, Lin HW - Sci Rep (2015)

GISAXS profiles of the vacuum-deposited CH3NH3PbI3−xClx films prepared at the substrate temperatures of 65, 75 and 85 °C, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4559897&req=5

f1: GISAXS profiles of the vacuum-deposited CH3NH3PbI3−xClx films prepared at the substrate temperatures of 65, 75 and 85 °C, respectively.
Mentions: Figure 1 shows the GISAXS profiles, I(Q), of the vacuum-deposited CH3NH3PbI3−xClx films at the substrate temperatures of 65, 75 and 85 °C, respectively. The GISAXS profiles show the behavior of power-law scattering with the characteristic of surface fractal (I(Q) ∝ Q−α; 3 ≤ α ≤ 4)3334. The exponent α is related to the surface fractal dimension Ds by Ds = 6-α. The surface fractal reveals that film surface has the morphology of self-similarity at different scales starting from nanometers, schematically showing in Fig. 2. The SAXS technique is particularly useful for characterizing fractal aggregation structures/or fractal morphology using the power-law scattering behavior over a wide Q range, which is reported by a large number of papers33343536. The general microscopic tools (SEM, AFM, TEM etc.) are very difficult to identify the fractal morphology. Therefore, the SAXS characterization of the fractal system is complementary to TEM observation. The local morphology observed through TEM may provide a very rough evidence of a fractal object at a certain length scale. The previous study37 reported the fractal morphology in the different perovskite solar cells studied by GISAXS technique, which was correlated to the SEM (for macroscale morphology of large grain) and TEM (nanoscale fractal pore network). This power-law scattering also implies that the internal structure of film comprised of perovskite grains is dense (solid-state) or there is almost no micropore inside the film (or no mesopore between grains). The GISAXS profiles (Fig. 1) shows that the fractal surface morphologies formed at 85 and 65 °C are very similar. In contrast, the surface morphology formed at 75 °C shows a larger scale, evidenced by the power-law scattering at the smaller Q region. This result is consistent with the SEM observation for the films prepared by the same procedure previously reported12. The SEM images showed that all films have the full surface coverage of μm-scale grains. The corresponding AFM measurement shows the Rrms values of ~23 nm. The previous study12 reported that the CH3NH3PbI3−xClx film prepared at 75 °C has much higher PCE (~15%) than those prepared at the other temperatures (6.1% and 4.5% for the subtract temperatures of 65 and 85 °C, respectively). It can be attributed to that the film prepared at 75 °C has the highest CH3NH3PbI3 crystallinity, evidenced by the simple one-dimensional (1D) XRD patterns previously reported12. It seems that the grain morphology is closely related to its crystalline structure and quality.

Bottom Line: The result is complementary to the currently microscopic study.The GISAXS/GIWAXS measurement provides the comprehensive understanding of concurrent evolution of the film morphology and crystallization correlated to the high performance.The result can provide the insight into formation mechanism and rational synthesis design.

View Article: PubMed Central - PubMed

Affiliation: Institute of Nuclear Energy Research, Longtan, Taoyuan 32546, Taiwan.

ABSTRACT
The structural characterization correlated to the processing control of hierarchical structure of planar heterojunction perovskite layer is still incomplete due to the limitations of conventional microscopy and X-ray diffraction. This present study performed the simultaneously grazing-incidence small-angle scattering and wide-angle scattering (GISAXS/GIWAXS) techniques to quantitatively probe the hierarchical structure of the planar heterojunction perovskite solar cells. The result is complementary to the currently microscopic study. Correlation between the crystallization behavior, crystal orientation, nano- and meso-scale internal structure and surface morphology of perovskite film as functions of various processing control parameters is reported for the first time. The structural transition from the fractal pore network to the surface fractal can be tuned by the chloride percentage. The GISAXS/GIWAXS measurement provides the comprehensive understanding of concurrent evolution of the film morphology and crystallization correlated to the high performance. The result can provide the insight into formation mechanism and rational synthesis design.

No MeSH data available.