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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.


Two dimensional GIWAXS patterns corresponding to the vacuum-deposited CH3NH3PbI3−xClx films prepared at the substrate temperatures of 65, 75 and 85 °C, respectively.
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f3: Two dimensional GIWAXS patterns corresponding to the vacuum-deposited CH3NH3PbI3−xClx films prepared at the substrate temperatures of 65, 75 and 85 °C, respectively.

Mentions: In this present study, all 2D GIWAXS patterns (Fig. 3) show the diffraction rings corresponding to the (110) and (220) planes at Q = 10 and 20 nm−1, respectively, being consistent with the CH3NH3PbI3−xClx crystal structure pattern2223. As shown in Fig. 3, the crystallites (/grains) with the (110) plane oriented (normal) to the out-of-plane direction dominates for all films25. The out-of-plane direction is perpendicular to the substrate or film surface (defined as Qz direction marked in the 2D GIWAXS pattern). These oriented crystallites are indicated by the clear diffraction spot in the Qz direction. The perovskite films prepared at 65 and 75 °C also show that a significant fraction of crystallites having the (110) plane oriented to the in-plane direction25, as indicated by the diffraction spot in the in-plane direction. The in-plane direction is parallel to the substrate or film surface (defined as the Qx direction also marked in Fig. 3). The relative crystallinity can be approximately represented by the azimuthally averaged intensity of diffraction (110) ring in the 2D GIWAXS pattern. The perovskite film prepared at 75 °C has the highest crystallinity and the largest amount of dominated crystallites with (110) plane oriented to the out-of-plane direction, evidenced by diffraction (110) spot. The new information revealed in this GIWAXS study is as follows: (1) For the film prepared at 65 °C, a fraction of CH3NH3PbI3−xClx crystallites rapidly decomposed into PbI2 crystallites23, as evidenced by the appearance of diffraction spot at Q = 9 nm−1 in the out-of-plane direction. (2) For the film prepared at 85 °C, a significant reduction of out-of-plane-oriented crystallites was accompanied by the formation of randomly-oriented crystallites, indicated by the isotropic distribution of diffraction ring in the 2D GIWAXS pattern (Fig. 3). The result suggests that the key parameter controlling or tuning the decomposition of vacuum-deposited CH3NH3PbI3−xClx crystallites into PbI2 is the substrate temperature. The literature20 pointed out that the existence of appropriate amount of PbI2 can protect from the interaction with oxygen and water. According to the azimuthally averaged intensities of GIWAXS patterns, the relative crystallinity of CH3NH3PbI3−xClx crystallites prepared at 85 °C is larger than that prepared at 65 °C. However, the PCE of the former (4.5%) is less than that of the latter (6.1%). It can be speculated that the grain boundary (GB) of all randomly-oriented crystallites forms an isotropic distribution of network. In contrast, 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. A recent literature reports that GB plays a beneficial role in collecting charge carriers efficiently38. It reveals that the influence of crystal orientation on the PCE is larger than that of crystallinity, showing the importance of the crystallites with the out-of-plane orientation. This case becomes critical for the films without high crystallinity. The high substrate temperature is the control factor changing the crystal orientation from the domination of the out-of-plane orientation to the random or isotropic orientation. The 2D GIWAXS patterns investigated here do not consider the geometric effect caused by the planar detector25, leading to large uncertainty. Therefore, we focus on the qualitative interpretation and relative comparison.


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)

Two dimensional GIWAXS patterns corresponding to 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

f3: Two dimensional GIWAXS patterns corresponding to the vacuum-deposited CH3NH3PbI3−xClx films prepared at the substrate temperatures of 65, 75 and 85 °C, respectively.
Mentions: In this present study, all 2D GIWAXS patterns (Fig. 3) show the diffraction rings corresponding to the (110) and (220) planes at Q = 10 and 20 nm−1, respectively, being consistent with the CH3NH3PbI3−xClx crystal structure pattern2223. As shown in Fig. 3, the crystallites (/grains) with the (110) plane oriented (normal) to the out-of-plane direction dominates for all films25. The out-of-plane direction is perpendicular to the substrate or film surface (defined as Qz direction marked in the 2D GIWAXS pattern). These oriented crystallites are indicated by the clear diffraction spot in the Qz direction. The perovskite films prepared at 65 and 75 °C also show that a significant fraction of crystallites having the (110) plane oriented to the in-plane direction25, as indicated by the diffraction spot in the in-plane direction. The in-plane direction is parallel to the substrate or film surface (defined as the Qx direction also marked in Fig. 3). The relative crystallinity can be approximately represented by the azimuthally averaged intensity of diffraction (110) ring in the 2D GIWAXS pattern. The perovskite film prepared at 75 °C has the highest crystallinity and the largest amount of dominated crystallites with (110) plane oriented to the out-of-plane direction, evidenced by diffraction (110) spot. The new information revealed in this GIWAXS study is as follows: (1) For the film prepared at 65 °C, a fraction of CH3NH3PbI3−xClx crystallites rapidly decomposed into PbI2 crystallites23, as evidenced by the appearance of diffraction spot at Q = 9 nm−1 in the out-of-plane direction. (2) For the film prepared at 85 °C, a significant reduction of out-of-plane-oriented crystallites was accompanied by the formation of randomly-oriented crystallites, indicated by the isotropic distribution of diffraction ring in the 2D GIWAXS pattern (Fig. 3). The result suggests that the key parameter controlling or tuning the decomposition of vacuum-deposited CH3NH3PbI3−xClx crystallites into PbI2 is the substrate temperature. The literature20 pointed out that the existence of appropriate amount of PbI2 can protect from the interaction with oxygen and water. According to the azimuthally averaged intensities of GIWAXS patterns, the relative crystallinity of CH3NH3PbI3−xClx crystallites prepared at 85 °C is larger than that prepared at 65 °C. However, the PCE of the former (4.5%) is less than that of the latter (6.1%). It can be speculated that the grain boundary (GB) of all randomly-oriented crystallites forms an isotropic distribution of network. In contrast, 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. A recent literature reports that GB plays a beneficial role in collecting charge carriers efficiently38. It reveals that the influence of crystal orientation on the PCE is larger than that of crystallinity, showing the importance of the crystallites with the out-of-plane orientation. This case becomes critical for the films without high crystallinity. The high substrate temperature is the control factor changing the crystal orientation from the domination of the out-of-plane orientation to the random or isotropic orientation. The 2D GIWAXS patterns investigated here do not consider the geometric effect caused by the planar detector25, leading to large uncertainty. Therefore, we focus on the qualitative interpretation and relative comparison.

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.