Performance Regulation of Cu2ZnPb x Sn1– x Se4– y S y Compounds and Optimization of Photodetectors: A Study Combining First-Principles Calculations with Device Simulations

Room-temperature mid- and far-infrared photodetectors are critical for next-generation sensing and communication, yet their development is severely hindered by the prohibitive cooling requirements of conventional state-of-the-art materials and the restricted 1200 nm cut-off wavelength of emerging earth-abundant absorbers like kesterite Cu2ZnSnSe4 (CZTSe). Herein, we propose a dual-site isovalent engineering paradigm of heavy-cation substitution coupled with light-anion compensation to shatter the intrinsic optoelectronic limits of CZTSe. Combining comprehensive first-principles calculations and macroscopic device simulations, we systematically investigate the Cu2ZnPbxSn1–xSe4–ySy solid solution series. The isomorphous substitution of Sn with bulky Pb atoms triggers a profound bandgap collapse down to an ultranarrow 0.042 eV via intense localized orbital reconstruction, successfully extending the absorption edge deep into the extreme far-infrared regime. Concurrently, gradient S alloying at the Se sites induces a uniform lattice contraction, which effectively relieves steric strain and precisely widens the bandgap, fundamentally suppressing the thermal generation-recombination dark currents inherent to narrow-bandgap architectures. Striking an optimal balance between bandgap engineering and carrier dynamics, the simulated room-temperature photodetector delivers a peak specific detectivity exceeding 1.5 × 1012 Jones and an unprecedented panchromatic response with a cut-off wavelength up to 29,500 nm. This synergistic compositional design strategy provides a robust atomic framework and a highly competitive material platform for the development of uncooled, ultra-broadband infrared optoelectronics.