Combinatorial Vacuum-Deposition of Metal Halide Perovskite Films and Solar Cells

The development of vacuum deposited perovskite materials and devices is partially slowed down by the minor research effort in this direction (at least when compared with the field of solution-processed perovskites), but also from one of its intrinsic characteristics: long timeframe for the optimization of even a single perovskite composition since in one deposition run only a single set of parameters can be used (i.e. set of deposition rates for a certain set of precursors). Combinatorial materials science (CMS) is a method that can be used to accelerate the study of compositionally varying perovskites. When CMS is applied to thin-films, a compositional gradient is deposited on purpose on a single large area substrate, referred to as a library, forming many different compounds or materials in a single deposition run. Here we report the combinatorial vacuum-deposition of wide bandgap perovskites of the type FA_1-nCs_nPb(I_1-xBr_x)₃, by using 4 sources and a non-rotating sample holder.[1] From initial deposition rates calculated based on stoichiometry and properties for each precursor, we run a combinatorial deposition and high throughput characterization. By using small pixel substrates, we are able to produce &gt;100 solar cells with different perovskite absorbers in a single deposition run. The materials are thoroughly characterized by spatially resolved and/or high throughput techniques, including optical, morphological and structural techniques. By subsequent fine tuning of the deposition rates, we can alter the gradient and reproduce the best performing formulations in standard depositions with rotation. We extended the method for optimizing wide bandgap CsMAFA triple-cation perovskite solar cells, which are found to be efficient but not thermally stable. With the aim of stabilizing the perovskite phase, we add guanidinium (GA⁺) to the material formulation, and obtained CsMAFAGA quadruple-cation perovskite films with improved thermal stability, as observed by X-ray diffraction and rationalized by microstructural analysis. The corresponding solar cells showed similar performance with a remarkable thermal stability, when compared to the triple-cation perovskite devices.[2] We believe this approach can encourage the discovery of materials, and serve as a basis to prototype other compositions (low bandgap, lead- free) overcoming the current limitations of vacuum deposition as a research tool for perovskite films.<br/><br/>[1] I. Susic, A. Kama, L. Gil Escrig*, C. Dreessen, F. Palazon, D. Cahen, M. Sessolo*, H. J. Bolink, Adv. Mater. Interf. 2022, Accepted for publication.<br/><br/>[2] I. Susic, L. Gil Escrig, F. Palazon, M. Sessolo*, and H. J. Bolink, ACS Energy Lett. 2022, 7, 4, 1355–1363