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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.


SEM images of the CH3NH3PbI3−xClx films prepared with 0, 10, 20 and 40% of chloride, respectively.
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f5: SEM images of the CH3NH3PbI3−xClx films prepared with 0, 10, 20 and 40% of chloride, respectively.

Mentions: Table 1 shows the structural parameters determined by the model fitting of Equation (1). Within the perovskite grains/or film prepared with 0% of chloride precursor (i.e., CH3NH3PbI3), there is an internal pore structure comprised of polydispersed primary pores of 3.3 nm in mean radius. The primary pores aggregate into a fractal network with fractal dimension of 1.8 and domain size (2Rg) of ~56 nm. This result is very close to the GISAXS analysis of the two-step solution-processed CH3NH3PbI3 film prepared by an independent group37. The openness and local channel morphology of the fractal pore network were consistently observed along the 3D direction by the secondary ion mass spectrometry and high-resolution TEM studies, respectively37, for validating the SAXS analysis model. Interestingly, the GISAXS profile (Fig. 4) of the perovskite film prepared with 10% of chloride demonstrates a distinctive fractal pore network. The radius of primary pore, pore fractal dimension and network domain determined by the model analysis (Table 1) are significantly enhanced to 4.0 nm, 2.6 and 115 nm, respectively. Why the internal pore network evolves into a 2D-like and larger domain can be attributed to the morphological evolution of CH3NH3PbI3−xClx perovskite film from the low-coverage aggregation of strip-like grains to the high-coverage aggregation of plane-like grains, as shown in the SEM observation (Fig. 5). Noticeably, when the chloride percentage is increased to 20%, an almost full coverage film is formed. The corresponding GISAXS profile (Fig. 4) shows a power-law scattering with the characteristic of surface fractal morphology (I(Q) ∝ Q−α; α = 3.7; Ds = 2.3) having a dense internal structure. Apparently, there is a structural transition from the internal pore network to surface fractal morphology. It is schematically shown in Fig. 2. It can be explained that the compact and high- density aggregation of perovskite grains forced the internal pores to collapse into a dense structure only with fractal morphology on the surface. Moreover, when the chloride percentage continues to increase to 40%, the aggregation of grains into film becomes over-coalescence and thus there appear a few holes between large grains (Fig. 5). The corresponding GISAXS profile shows the surface fractal morphology with fractal dimension α of ~3.0 (Ds = 3). The increase in surface fractal dimension reflects that the surface roughness becomes larger. The AFM measurement consistently shows that the Rrms values of the films prepared with 20 and 40% chloride precursor are 23.8 and 133 nm, respectively. The corresponding AFM images for the four perovskite films are shown in the supporting information (Figure S1). Compared to the microscopic observation, the GISAXS analysis can provide the insight into the 3D internal fractal pore structure and surface fractal morphology of CH3NH3PbI3−xClx perovskite films at the nano- and meso-scale. Moreover, tuning the chloride content for the one-step processing to induce the structural transition from the internal pore network to the surface fractal morphology is reported for the first time. It provides the useful information to fabrication design and optimization.


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)

SEM images of the CH3NH3PbI3−xClx films prepared with 0, 10, 20 and 40% of chloride, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: SEM images of the CH3NH3PbI3−xClx films prepared with 0, 10, 20 and 40% of chloride, respectively.
Mentions: Table 1 shows the structural parameters determined by the model fitting of Equation (1). Within the perovskite grains/or film prepared with 0% of chloride precursor (i.e., CH3NH3PbI3), there is an internal pore structure comprised of polydispersed primary pores of 3.3 nm in mean radius. The primary pores aggregate into a fractal network with fractal dimension of 1.8 and domain size (2Rg) of ~56 nm. This result is very close to the GISAXS analysis of the two-step solution-processed CH3NH3PbI3 film prepared by an independent group37. The openness and local channel morphology of the fractal pore network were consistently observed along the 3D direction by the secondary ion mass spectrometry and high-resolution TEM studies, respectively37, for validating the SAXS analysis model. Interestingly, the GISAXS profile (Fig. 4) of the perovskite film prepared with 10% of chloride demonstrates a distinctive fractal pore network. The radius of primary pore, pore fractal dimension and network domain determined by the model analysis (Table 1) are significantly enhanced to 4.0 nm, 2.6 and 115 nm, respectively. Why the internal pore network evolves into a 2D-like and larger domain can be attributed to the morphological evolution of CH3NH3PbI3−xClx perovskite film from the low-coverage aggregation of strip-like grains to the high-coverage aggregation of plane-like grains, as shown in the SEM observation (Fig. 5). Noticeably, when the chloride percentage is increased to 20%, an almost full coverage film is formed. The corresponding GISAXS profile (Fig. 4) shows a power-law scattering with the characteristic of surface fractal morphology (I(Q) ∝ Q−α; α = 3.7; Ds = 2.3) having a dense internal structure. Apparently, there is a structural transition from the internal pore network to surface fractal morphology. It is schematically shown in Fig. 2. It can be explained that the compact and high- density aggregation of perovskite grains forced the internal pores to collapse into a dense structure only with fractal morphology on the surface. Moreover, when the chloride percentage continues to increase to 40%, the aggregation of grains into film becomes over-coalescence and thus there appear a few holes between large grains (Fig. 5). The corresponding GISAXS profile shows the surface fractal morphology with fractal dimension α of ~3.0 (Ds = 3). The increase in surface fractal dimension reflects that the surface roughness becomes larger. The AFM measurement consistently shows that the Rrms values of the films prepared with 20 and 40% chloride precursor are 23.8 and 133 nm, respectively. The corresponding AFM images for the four perovskite films are shown in the supporting information (Figure S1). Compared to the microscopic observation, the GISAXS analysis can provide the insight into the 3D internal fractal pore structure and surface fractal morphology of CH3NH3PbI3−xClx perovskite films at the nano- and meso-scale. Moreover, tuning the chloride content for the one-step processing to induce the structural transition from the internal pore network to the surface fractal morphology is reported for the first time. It provides the useful information to fabrication design and optimization.

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.