Performance analysis of DMF-free perovskite solar cells with vacuum quenching

In pursuit of perovskite solar cells compatible with silicon tandem cells, we have been exploring the vacuum quenching method. Given that N,N-dimethylformamide (DMF) is a known carcinogen in animals, we used a mixed solvent of 1-Methyl-2-pyrrolidone and Dimethyl Sulfoxide as safer alternatives. We optimized the vacuum quenching method by adjusting parameters such as annealing temperature and additives to the ink to achieve higher efficiency. We present the characteristics and structural features of solar cells in which perovskite layers were crystallized using this optimized vacuum quenching method. We fabricated a DMF-free vacuum quenched p-i-n CsFAMAPb(I/Br)3 perovskite solar cell with an energy gap (Eg) of 1.69 eV and an effective area of 1.04 cm2. We then evaluated its current-voltage characteristics using the 4-terminals method. A peak power conversion efficiency of 17.0% in the forward scan and 13.2% in the reverse scan was achieved without passivation, and 18.0% in the forward scan and 17.1% in the reverse scan by incorporating 0.5% 2-Phenylethylamine Hydroiodide (PEAI) into the perovskite ink. We measured photoluminescence spectra of perovskite crystal thin films, prepared under the same conditions as the solar cells. The photoluminescence spectra showed a consistent pattern across all samples with two gaussian components. As the conditions were optimized, the component on the high-energy side approached the intended bandgap. Furthermore, upon the addition of PEAI, the band-edge was accentuated. The XRD results indicate that the major peaks can be attributed to the cubic perovskite structure. The addition of PEAI does not significantly change the peak positions or intensities, but it reduces a minor peak attributed to PbI2, suggesting suppressed PbI2 precipitation. Our results indicate that the optimized conditions for vacuum quenching can produce perovskite crystals without undesirable precipitates, leading to an increase in the efficiency of solar cells.