Roughness and structural modification of PbI2 thin films by isopropanol treatment to improve methylammonium lead halide formation and solar cell efficiency

• Published in: Journal of materials science. Materials in electronics Vol. 30; no. 18; pp. 17491 - 17503
• Main Authors: Moreno-Romero, Paola M., Corpus-Mendoza, Asiel N., Millán-Franco, Mario A., Rodríguez-Castañeda, Carlos A., Torres-Herrera, D. Mateus, Liu, Feng, Hu, Hailin
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.09.2019; Springer Nature B.V
• Subjects: Atomic force microscopy; Characterization and Evaluation of Materials; Chemistry and Materials Science; Crystal structure; Crystallinity; Energy conversion efficiency; Fractal analysis; Grain size; Isopropanol; Lead compounds; Materials Science; Metal halides; Morphology; Optical and Electronic Materials; Perovskites; Photovoltaic cells; Self-similarity; Solar cells; Spin coating; Statistical methods; Surface roughness; Thin films
• ISSN: 0957-4522; 1573-482X
• DOI: 10.1007/s10854-019-02100-7

Perovskite thin films can be prepared by two-step spin coating technique, in which lead iodide (PbI 2 ) is first deposited followed by methylammonium halide. The addition of isopropanol (IPA) in the first deposition leads to more porous and less crystalline PbI 2 thin films. To understand the effect of IPA treatment, we study the surface morphology parameters of PbI 2 thin films by using statistical fractal analysis on their Atomic Force Microscopy images at different image scales. We found that the surface roughness of IPA-treated PbI 2 layer (r-PbI 2 ) is almost twice than that of the PbI 2 layer without such treatment (c-PbI 2 ). Moreover, the surface of r-PbI 2 thin films shows a self-similar characteristic, which means that the roughness pattern may repeat at different scales. This is confirmed by perfilometry measurement, showing a uniform roughness pattern of r-PbI 2 samples in a millimeter scale. Furthermore, larger grain size and crystallinity of perovskite thin films are obtained with r-PbI 2 , independent of the partial substitution of iodide by chloride or bromide. The perovskite solar cells based on r-PbI 2 exhibit average power conversion efficiency (PCE) of 10.27% over 127 cell samples, whereas those fabricated with c-PbI 2 films show a lower average PCE of 7.20% over 107 samples.