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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.


XRD patterns (a) in linear and (b) in logarithmic scale of the CH3NH3PbI3−xClx films prepared with 0, 10, 20 and 40% of chloride, respectively.
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f7: XRD patterns (a) in linear and (b) in logarithmic scale of the CH3NH3PbI3−xClx films prepared with 0, 10, 20 and 40% of chloride, respectively.

Mentions: The film coverage of the perovskite layer prepared with 10% of chloride is much better than that of the layer prepared with 40% of chloride. The former also has an open internal pore network, which seems to be favorable to the dissociation and transport of charge However, The PCE (4.92%) of the former is much less than that (11.4%) of the latter. As shown in Fig. 6, the light absorption spectra and EQE spectra for the investigated perovskite films are consistent with the measured PCE values (in order, 20% > 40% > 10% > 0%, expressed by chloride ratio). The higher absorbance for the 20% Cl of sample is mainly due to the best surface coverage and almost pinhole free morphology of the perovskite thin film, which is revealed in the SEM image as shown in Fig. 5. Other samples exhibit much higher pin-hole (void) densities which largely decrease the absorbance of the thin films. The high coverage of the film is one of necessary conditions for improving the performance. Except for the perovskite film with the highest PCE and full coverage (prepared with 20% of chloride), the morphological structure cannot be reasonably correlated to the performance. Therefore, the crystallinity of perovskite layer should be main parameter contributing to the photovoltaic performance and properties. However, the conventional XRD measurement for all investigated films (Fig. 7) shows that their (110) peak intensities (2θ = 14.3o) have no significant difference and the order of 40% > 20% > 10% > 0% (expressed by chloride ratio), which is not consistent with the PCE result. Noticeably, the GIWAXS result (Fig. 8) can be reasonably correlated to the PCE values. According to 2D GIWAXS patterns, the comparison between the intensities of the out-of-plane (110) diffraction spots of perovskite crystallites (in the Qz direction in Fig. 8) demonstrates the substantial difference in the order of 20% > 40% > 10% > 0%, being consistent with the performance. This present study reveals that the simultaneous GISAXS/GIWAXS analysis can give complete interpretation to the relation between structure and performance. The crystallites with the strong out-of-plane orientation (i.e., the direction normal to the film surface) of (110) plane, shown by 2D GIWAXS (or GIXRD) measurement, is closely related to the high device performance. According to the recent literature38, the grain boundary (GB) of crystallites plays a beneficial role in collecting charge carriers efficiently. We speculate that the GB network formed by the dominated crystallites with the out-of-plane orientation (normal to the film surface) has an alignment structure which is more favorable to the transport of charge carrier than that of the crystallites with other orientations. We also correlate the nanomorphology of the films to the crystal orientation. For the perovskite films with internal pore network (prepared with 0% and 10% of chloride), the crystallites oriented to the out-of-plane direction dominate. No crystallites with the in-plane orientation were apparently observed. The dense perovskite films with surface fractal morphology (prepared with 20% and 40% of chloride) have the crystallites with out-of-plane as well as in-plane orientations. The film with over-coalesced grains (40% of chloride) has highly-ordered perovskite structure (as shown by the other spots at high Q region between Qz and Qx directions in Fig. 8).


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)

XRD patterns (a) in linear and (b) in logarithmic scale 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

f7: XRD patterns (a) in linear and (b) in logarithmic scale of the CH3NH3PbI3−xClx films prepared with 0, 10, 20 and 40% of chloride, respectively.
Mentions: The film coverage of the perovskite layer prepared with 10% of chloride is much better than that of the layer prepared with 40% of chloride. The former also has an open internal pore network, which seems to be favorable to the dissociation and transport of charge However, The PCE (4.92%) of the former is much less than that (11.4%) of the latter. As shown in Fig. 6, the light absorption spectra and EQE spectra for the investigated perovskite films are consistent with the measured PCE values (in order, 20% > 40% > 10% > 0%, expressed by chloride ratio). The higher absorbance for the 20% Cl of sample is mainly due to the best surface coverage and almost pinhole free morphology of the perovskite thin film, which is revealed in the SEM image as shown in Fig. 5. Other samples exhibit much higher pin-hole (void) densities which largely decrease the absorbance of the thin films. The high coverage of the film is one of necessary conditions for improving the performance. Except for the perovskite film with the highest PCE and full coverage (prepared with 20% of chloride), the morphological structure cannot be reasonably correlated to the performance. Therefore, the crystallinity of perovskite layer should be main parameter contributing to the photovoltaic performance and properties. However, the conventional XRD measurement for all investigated films (Fig. 7) shows that their (110) peak intensities (2θ = 14.3o) have no significant difference and the order of 40% > 20% > 10% > 0% (expressed by chloride ratio), which is not consistent with the PCE result. Noticeably, the GIWAXS result (Fig. 8) can be reasonably correlated to the PCE values. According to 2D GIWAXS patterns, the comparison between the intensities of the out-of-plane (110) diffraction spots of perovskite crystallites (in the Qz direction in Fig. 8) demonstrates the substantial difference in the order of 20% > 40% > 10% > 0%, being consistent with the performance. This present study reveals that the simultaneous GISAXS/GIWAXS analysis can give complete interpretation to the relation between structure and performance. The crystallites with the strong out-of-plane orientation (i.e., the direction normal to the film surface) of (110) plane, shown by 2D GIWAXS (or GIXRD) measurement, is closely related to the high device performance. According to the recent literature38, the grain boundary (GB) of crystallites plays a beneficial role in collecting charge carriers efficiently. We speculate that the GB network formed by the dominated crystallites with the out-of-plane orientation (normal to the film surface) has an alignment structure which is more favorable to the transport of charge carrier than that of the crystallites with other orientations. We also correlate the nanomorphology of the films to the crystal orientation. For the perovskite films with internal pore network (prepared with 0% and 10% of chloride), the crystallites oriented to the out-of-plane direction dominate. No crystallites with the in-plane orientation were apparently observed. The dense perovskite films with surface fractal morphology (prepared with 20% and 40% of chloride) have the crystallites with out-of-plane as well as in-plane orientations. The film with over-coalesced grains (40% of chloride) has highly-ordered perovskite structure (as shown by the other spots at high Q region between Qz and Qx directions in Fig. 8).

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.