Combinatorial slot-die coating for high-throughput compositional screening of perovskite solar cells

Abstract

We here present a generic methodology enabling the accelerated optimization of the composition and processes conditions for functional solution-processable materials compatible with later transfer of optimized conditions to scaled device manufacturing. In combinatorial slot-die coating, two or more precursor inks are fed with different rates into the slot-die enabling fast screening of the precursor solution composition on coating property in one experimental run, which can either be implemented as consecutive coatings with different compositions or as a continuous compositional gradient. As a first example, we here present combinatorially slot-die coated halide perovskite thin-films ranging from the precursor compositions of pure formamidinium lead iodide, FAPbI3, to methylammonium lead bromide, MAPbBr3. In this series, both the optical and morphological properties of the deposited thin-films change dramatically. An increasing faction of MAPbBr3 resulted in larger optical bandgaps. At very high MAPbBr3 ratios, differences in the thin-film crystallization kinetics due to the simultaneous change of the precursor solution solvent resulted in thin-films with low quality morphology. The spatial compositional homogeneity of the coated thin-films was characterized by grazing incidence wide angle X-ray scattering mapping. We fabricated inverted perovskite solar cells in the full compositional range and found a performance maximum for FAPbI3-richer devices with a MAPbBr3-content of 20 mol%. The performance maximum can be rationalized with the improved thermodynamic stability of the halide perovskite crystal structure due to a more ideal tolerance factor upon incorporation of the smaller methylammonium cation and bromide anion into the crystal structure. At high MAPbBr3-content, the device performance drops due to two effects: light-induced phase-segregation and a dramatically decreased thin-film morphology exhibiting pinholes. The example highlights the critical balance of precursor solution composition and processing conditions as the crystallization kinetics critically affect the resulting thin-film quality and morphology. This generic methodology can be further optimized and exploited to identify optimal precursor solution compositions and process conditions to achieve high-quality thin films with a target composition and sample morphology with high experimental throughput.