Jian Cheng, Mao‐Yin Ran, Zi-Nan Chen, Sheng‐Ping Guo
ABSTRACT Balancing the second‐harmonic generation (SHG) intensity with laser‐induced damage threshold (LIDT) while achieving phase‐matchability presents a significant challenge for infrared nonlinear optical (NLO) materials. The high‐entropy strategy enables synergistic regulation of properties through multi‐component interactions, effectively addressing the limitations of conventional materials such as unitary functionality and inadequate stability. In this work, a series of defect wurtzite‐derived selenides, namely Al 0.09 In 1.91 Se 3 , Al 0.25 In 1.75 Se 3 , Al 0.5 In 1.5 Se 3 , and Al 0.61 In 0.39 Se 3 , were obtained via the high‐entropy assembly of MSe 4 (M = Al/In) tetrahedral units with high polarizability and InSe 5 trigonal bipyramidal units capable of tuning anisotropy. The achieved “cocktail effect” addresses the issue that wurtzite‐derived compounds hardly achieve phase matchability due to ultralow birefringence, and enables them to exhibit wonderful integrated NLO performances. Most notably, this series exhibits the strongest SHG efficiency (1.1–1.9 × AGS) among Al‐based chalcogenides, high laser‐induced damage thresholds (3.6–7.3 × AGS), and moderate birefringence (0.06–0.14) suitable for phase‐matching behavior. First‐principles calculations elucidate that the enhanced SHG response originates from helically aligned MSe 4 tetrahedra, while the birefringence modulation principally arises from the highly distorted InSe 5 trigonal bipyramidal motifs. This entropy‐driven strategy for regulating NLO properties provides an efficient, feasible, and novel pathway for the design and development of high‐performance NLO materials.