Efficient Narrowband Photoconductivity of the Excitonic Resonance in Two-Dimensional Ruddlesden-Popper Perovskites Due to Exciton Polarons

Filter-less, wavelength-selectivephotodetectors made of perovskiteusually rely on the charge collection narrowing mechanism, which intrinsicallylimits the response times. Using the narrow excitonic peak of, e.g.,two-dimensional (2D) Ruddlesden-Popper perovskites as directabsorbers to realize color-selective photodetectivity promises fasterresponses. However, one major challenge in realizing such devicesremains the separation and charge carrier extraction of the tightlybound excitons. Here, we report on filter-less color-selective photoconductivityin 2D perovskite butylammonium lead iodide thin film devices, exhibitinga distinct resonance in the photocurrent spectrum with a full widthat half-maximum of 16.5 nm that correlates to the excitonic absorption.Our devices exhibit unexpectedly efficient charge carrier separationwith an external quantum efficiency of <= 8.9% at the excitonicresonance, which we trace back to the involvement of exciton polarons.Our photodetector achieves response times of 150 mu s and a maximumspecific detectivity of 2.5 x 10(10) Jones at the excitonicpeak.