Texture of strongly oriented MAPbI3 studied by wide reciprocal-space mapping

Lukáš Horák¹, Amalraj Peter Amalathas², Jakub Holovský^2,3

¹Charles University, Faculty of Mathematics and Physics, Prague, Czech Republic

² Centre for Advanced Photovoltaics, Faculty of Electrical Engineering, Czech Technical University in Prague, 166 27 Prague, Czech Republic

³Institute of Physics, Czech Academy of Sciences, 162 00 Prague, Czech Republic

horak@karlov.mff.cuni.cz

Polycrystalline organic perovskites such as CH₃NH₃PbI₃ (MAPbI3) quite often form strongly oriented polycrystalline layers with complex multicomponent fibre texture. Prefererential orientation as well as other microstructure parameters of MAPbI3 layers are strongly affected by the preparation procedure [1] and are correlated with the stability and performance of the final sollar cells. We observed the change in texture composition and the degradation rate for different concentrations of MACl additive (0 % – 3 %) present during the preparation of the MAPBI3 layer preparation.

PXRD patterns (Bragg-Brentano) for MAPbI3 (MACl-assisted preparation) have been collected for different MACl concentrations. Mainly MAPbI3 hh0 peaks are present due to the strong (110) texture. The degradation of the sample over time is manifested by the appearance of PbI2 Bragg reflections, their intensities correlate with MACl concentration. Quite often people use only these intensities to compare the “crystallinity degree” and stability. This simplification can lead to data misinterpretation, since the texture which differs for various samples is completely neglected. In our case, further peaks are also visible for higher MACl concentration, and at least semi-quantitative texture analysis is necessary.

In order to fully determine the texture of the layers, one can use well-established but time consuming pole-figure measurement; however, it is not very optimal for materials with large low-symmetric unit cells. Here the number of observable peaks is high, therefore their diffraction angles are partially overlapping, and further possible strain can induce some peak shift. On the other hand, in this case it is very convenient to use a fast reciprocal space mapping method, which is quite fast and it can be used blindly without prior knowledge of the peak positions because the whole cut of reciprocal space is recorded and analyzed ex post.

Figure 1. Wide Reciprocal Space Maps for the MAPbI3 thin layers grown with and without the presence of MACl additive. Transparent spots represent simulated peak positions for the same MAPbI3 structure, the texture components are resolved by different colours: (110) by red, (021) by green, and (130) by cyan.

The concentration of MACl during growth determines the final texture of the layer as shown in Figure 1. A low concentration results in a multi-component texture. The strongest (110) major component is accompanied by medium-populated (021) component and weak (130) component. On the contrary, a high concentration MACl additive enhances just one single preferential orientation (110).

1. A. P. Amalathas, L. Landová, Z. Hájková, L. Horák, M. Ledinsky, and J. Holovský, ACS Appl. Energy Mater. 2020, 3, 12, 12484−12493

The work was supported by the project GA ČR, reg. No. 23-06543S