Lead-free materials based on the (Ba,Ca)(Zr,Ti)O3 (BCZT) system exhibit excellent electromechanical properties that can be strongly modified by small amounts of dopants. Here, we use a combinatorial strategy to unravel the influence of aliovalent doping with Ce on dielectric and piezoelectric properties of BCTZ. We synthesize and characterize a single BCTZ thin film with a composition gradient from undoped to 0.2 mol % cerium doping. The cerium doping increases the piezoelectric coefficient from 42.3 ± 2.9 pm V–1 (undoped) to 63.0 ± 2.4 pm V–1 for 0.06 Ce-mol %, and then decreases to 38.4 ± 1.3 pm V –1 for the maximum amount of cerium (0.2 mol %). An investigation of subcoercive field nonlinearities reveals that these variations are not only induced by changes in dynamics and densities of domain walls. The results highlight the advantage of combinatorial techniques to identify ideal compositions for applications without synthesizing a high number of samples with unavoidable sample-to-sample variations.