for various research fields ranging from lasing, light emitting devices (LEDs) to photo-or particle-detection. [10][11][12] Importantly, the bandgap tuning is achieved by interchanging the above cations, metals, or halides.For single-junction solar cells, frequently FA is selected as the majority cation because of the increased thermal stability and the redshifted bandgap compared to the volatile MA. However, the relatively large size of FA distorts the perovskite lattice exhibiting polymorphism, i.e., a photoinactive "yellow" phase at room temperature and a photoactive "black" phase at elevated temperatures. [3] Recently, many groups have realized that mixing the cation (or halide) position dramatically improves film morphology and optoelectronic properties. With hindsight, the mixing approach can be correlated with the steep performance increases over the past years. [13,14] Such "alloyed" polyelemental compositions have mainly focused on double-cation mixtures such as CsFA or MAFA perovskites, with a fixed halide ratio of Br and I, effectively inducing a stable black FA-phase at room temperature. [13,[15][16][17] The mixing approach was continued with CsMAFA triple-cation perovskites showing superior efficiency, reproducibility and stability as well as suppressed "yellow" phase impurities. This firstgeneration cation mixing of Cs, MA and FA was guided by past research demonstrating a black phase for the well-known Cs-, MA-, and FA-PbI 3 perovskites. [18] As a next step, going beyond "naïve" mixing of already established cations, the small Rb, that does not form a black phase as a single-component perovskite, was used in a multication engineering approach. [19] This entails an interesting observation: adding a new component results in a doubling of the combinatorial amount of compositions with the potential for unique and highly desirable properties that were previously not anticipated-as in the case of CsFA perovskites that suppressed halide segregation. [17] Any of the new compounds could become therefore highly relevant for industrialization.The mixing approach, however, is not exclusive to the cation position. There are metal mixtures, e.g., Sn-Pb or Ge-Sn, [5,20,21] or anion mixtures, e.g., double (Br/I) [13,14] and even triple halides (Cl/Br/I). [22,23] This provides a myriad of possible combinations necessitating careful planning to fully follow through with the polyelemental, multicomponent theme.The sheer number of combinatorically available precursor components makes a brute-force approach very laborious and Recently, perovskites with multiple cations, metals, and anions have shown very high efficiencies and stabilities for perovskite solar cells. The novel materials frequently exhibit unexpected and beneficial properties, outperforming simpler counterparts. The trend of increasing material complexity requires a systematic strategy to explore polyelemental "multicomponent engineering." Here, a combinatorial approach is introduced to generate all possible, unique combinations within a set of available ...