The power conversion efficiencies (PCEs) of lead halide perovskite (LHP) solar cells have improved significantly during the last years and reached values of up to 25 %. However, large PCE differences can be observed even when similar precursors and production methods are used. One possible reason for this finding is the existence of small differences in the colloidal precursor solutions.

Anita W. Y. Ho-baillie, University of New South Wales, Sydney, Australia, Min Gyu Kim, Pohang University of Science and Technology, Republic of Korea, Sang Il Seok, Ulsan National Institute of Science and Technology, Republic of Korea, and colleagues have investigated the influence of LHP precursor solutions on the properties of the resulting perovskite films. The precursor solutions were prepared from methylammonium iodide (MAI) and PbI₂, dissolved in a 4:1 mixture of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). Varying small amounts of an I₃^– solution were added. The precursor material was then heated and deposited onto a TiO₂ layer on a fluorine-doped tin oxide (FTO)-coated glass.

The precursor solutions were analyzed by UV-Vis spectroscopy to control the iodine content. The colloidal size was measured by dynamic light scattering, which showed a reduction of particle radius at higher iodine concentrations. The formation of iodoplumbate clusters during the heating of the precursor was monitored by temperature-dependent in-situ X-ray absorption fine structure (EXAFS) spectroscopy. The resulting films were analyzed by atomic force microscopy (AFM), transmission electron microscopy (TEM), and X-ray diffraction.

The highest quantum yield was achieved using the samples with the most ordered crystalline structure. The researchers observed a strong effect of small differences in the properties of the precursor materials on the device efficiency of the final perovskites. They emphasize the importance of the precursor composition for achieving optimal performance in LHP solar cells.

• Unveiling the Relationship between the Perovskite Precursor Solution and the Resulting Device Performance,
  Jincheol Kim, Byung-wook Park, Jongho Baek, Jae Sung Yun, Hyoung-Woo Kwon, Jan Seidel, Hanul Min, Simao Coelho, Sean Lim, Shujuan Huang, Katharina Gaus, Martin A. Green, Tae Joo Shin, Anita W. Y. Ho-baillie, Min Gyu Kim, Sang Il Seok,
  J. Am. Chem. Soc. 2020.
  https://doi.org/10.1021/jacs.0c00411