Rational composition engineering for high-quality Pb–Sn photodetector toward sensitive near-infrared digital imaging arrays

Broadband photodetectors (PDs) capable of multi-wavelength detection have garnered significant interest for applications in environmental monitoring, optical communication, spectral analysis, and imaging sensing. Low-bandgap Pb–Sn hybrid perovskite photodetectors can extend the spectral response from the ultraviolet–visible (UV–vis) range to the near-infrared (NIR) and reduce the toxicity associated with Pb²⁺. The strategic introduction of Sn²⁺ into Cs_0.15FA_0.85Pb_xSn_1−xI₃ (x = 1, 0.8, 0.6, 0.5, 0.4, 0.2, and 0) not only preserves the cubic crystal structure with conformal multigrain growth but also broadens the film's absorption spectrum from 800 to 1000 nm NIR region. This indicates a well-controlled tunability of the Pb–Sn binary perovskite system. Specifically, the self-powered photodetector with a device structure of ITO/NiO_x/PTAA/Cs_0.15FA_0.85Pb_0.5Sn_0.5I₃/PCBM/BCP/Ag has shown remarkable optoelectrical properties. It exhibits a high external quantum efficiency (EQE) of up to 80% across the spectrum from 300 to 1000 nm, a responsivity (R) exceeding 0.5 A/W, and high detectivity (D*) value of 1.04 × 10¹² Jones at 910 nm and 3.38 × 10¹¹ Jones at 1000 nm after weak attenuation. Intriguingly, the dark current of the Cs_0.15FA_0.85Pb_0.5Sn_0.5I₃ device is four orders of magnitude lower than that of devices made with pristine Pb or Sn only, strongly correlating with its significantly increased built-in potential and reduced trap density. Consequently, it demonstrates a −3 dB bandwidth of 2.23 × 10⁴ Hz, fast rise and decay times of 61 and 30 μs, respectively, and a linear dynamic range (LDR) of 155 dB. Benefiting from its high sensitivity, a 5 × 5 PD array for NIR imaging and non-invasive pulse detection for photoplethysmography applications has been successfully demonstrated, showcasing the prosperous potential of Pb–Sn hybrid perovskite in the NIR range.