Mega broadband photoresponsivity in degradation-controlled super-halide PF₆ substituted Perovskite@graphene hybrid photodetectors

We present, probably for the first time, the use of super-halide PF₆ as a substitution for iodine in the bulk precursor phase of FAPbI₃ for stable perovskite@graphene photodetectors. Our novel approach confers improved stability of perovskite, as demonstrated by synchrotron-based time-dependent nano-X-ray Fluorescence mapping of iodine. We observed a predominantly high α-phase (with weaker δ and PbI₂ phases) in the superior 10 % PF₆-substituted perovskite, as revealed by synchrotron-based GIWAXS. Our FAPbI_3-x(PF₆)_x@graphene photodetectors exhibited exceptional performance under power-dependent broadband illumination. In contrast to pure FAPbI₃@graphene devices (x = 0), which showed time-dependent bi-directional photoresponse indicative of degradation, our 10 % PF₆-substituted perovskite@graphene devices (x = 0.1) displayed unprecedented, positive, and stable photoresponsivity (∼1.01 × 10⁶ A W⁻¹), along with a high detectivity (D*) of 5 × 10¹⁴ Jones. Our devices also demonstrated remarkable sensitivity to signals from domestic appliances, exhibiting response times ranging from 93 to 101 ms. We model the photodetection mechanism using experimental band structure measurements to explain our results. Our findings suggest that our FAPbI_3-x(PF₆)_x@graphene photodetectors hold great promise for a range of applications in the fields of optoelectronics and sensing. In addition, our findings can contribute to the development of more stable and efficient perovskite solar cells, thereby advancing the solar cell research field.