Solution-processed metal halide perovskite photodetectors (PPDs) have a great potential in visible and near-infrared light sensing and X-ray imaging applications, owing to their excellent optoelectronic properties. This presentation will consist of two parts. After a brief survey of the advantages of solution-processed perovskites in high-resolution, flexible large-area imagers we will focus on better understanding the physical mechanisms that determine the dark current density and detectivity of thin-film photodetectors in the first part [1].

We will demonstrate that extrinsic leakage current at the periphery of the bottom pixel electrode is greatly reduced by introducing a so-called pixel edge cover layer. When such an edge cover layer is inserted, the dark current density decreases to ~10−6 mA cm−2 at −0.5 V, which is among the lowest values reported for polycrystalline PPDs.1 Moreover, the dark current density becomes independent of pixel size, up to 1000 ppi. To reduce dark current density even further, we carefully investigated a range of charge blocking layers, effectively reducing the dark current density even further.

By combining the appropriate blocking layer with the edge cover, a perovskite thin-film photodiode was fabricated that has a spectral responsivity of 0.5 A/W at 950 nm (Fig. 1a), combined with an ultralow dark current density of 5 × 10−8 mA cm−2 (Fig. 1b) and noise current of 2 × 10−14 A Hz−1/2 .

In the second part we will present recent developments in realizing three prototypical applications, i.e. a paper-thin photo-imager [2], a direct conversion X-ray detector [3] and a novel narrowband optical sensor that can measure a person’s heartbeat and respiration rate from a distance of over one meter using NIR light [4].

Including thin-film encapsulation layers - required to guarantee a long lifetime - the photo-imager [2] is only ca. 100 mm thick and can be wrapped around a non-flat object (radius of curvature of 0.6 cm). The wrapping ensures the close proximity between sensor surface area and a curved object, effectively increasing the area of the object that can be imaged with high-resolution. This is relevant for instance for nail-to-nail fingerprint imaging. Biometric fingerprinting is demonstrated with liveness detection.

The resulting direct-conversion X-ray detector [3] has a low detection limit of 0.22 nGyair frame-1, a sensitivity of 1060 µCGyair-1cm-2 (at a bias of 0.03 V µm−1) with a high spatial resolution of 6 line-pairs mm-1.

Finally, we report an inherently-narrowband solution-processed, thin-film photodiode with ultrahigh and controllable NIR responsivity based on a tandem-like perovskite-organic architecture [4]. The device possesses low dark currents (< 10−6 mA cm−2), linear dynamic range > 150 dB, and operational stability over time (> 8 h). With a narrowband quantum efficiency that can exceed 200% at 850 nm and intrinsic filtering of other wavelengths to limit optical noise, the device exhibits higher tolerance to background light than optically-filtered silicon-based sensors.