Noble Metals Doping in Lead-Free Double Perovskite Single Crystals: Achieving Near-Infrared to X-ray Broadband Photodetection.

Semiconductor materials capable of broadband photodetection, spanning X-rays to near-infrared (NIR), are essential for applications in medical imaging, industrial inspection, security, and telecommunications. Conventional photodetectors like Si, Ge, InGaAs, and amorphous Se (a-Se) often encounter tradeoffs in efficiency or cost-effectiveness. Halide perovskites (HPs) offer competitive or superior optoelectronic properties with low-cost, solution-based processing. However, lead-based HPs pose toxicity and stability challenges, while lead-free tin-based HPs suffer from Sn²⁺ oxidation and structural degradation. The lead-free double perovskite Cs₂AgBiBr₆ has emerged as a stable, nontoxic alternative for X-ray and visible-light photodetection. Despite its advantages, its high bandgap (≈1.9 eV) limits NIR absorption. This study explores doping Cs₂AgBiBr₆ with noble metal cations (Au³⁺, Pd²⁺, and Ir³⁺) to lower its absorption onset and enhance its photodetection capabilities across a broad spectrum. The results demonstrate that noble metal doping can overcome the intrinsic limitations of pristine Cs₂AgBiBr₆, enabling efficient photodetection from X-rays to the NIR range. This approach highlights a viable pathway for developing next-generation broadband photodetectors that combine nontoxicity, stability, and wide-spectrum sensitivity.