To further explore the ternary compositional space and thereby realize the optimized 3D-like HP matrix for the PV applications, we employ a newly developed Gated-GPBO approach to drive the exploration within the compositional space. We first implement a classical GPBO which solely takes account into the PL intensity of the films (Figure ). In the Gated-GPBO, an additional GP model that takes accounts into an instability score to find the compositions that render a stable PL peak that is close to the target wavelength (>600 nm). Details regarding the Gated-GPBO approach can be found in Methods. The Gated-GPBO predicted ternary diagrams manifesting the target functionalities are shown in Figure . It is found that the target functionality intensely emerges close to the compositional space where NMF is predicted (Phase Set 4 in Figure ). Specifically, it visualizes a narrow channel along the ~50% CsPbI3 line profile. We refine a ternary composition 66:20:14 as a Gated-GPBO-designed composition, which is collectively shown with the NMF-predicted compositions in Figure .