Off-Stoichiometric Perovskite Photodetectors for Direct Time-Of-Flight Distance Measurements

Hybrid organic-inorganic metal halide perovskites have recently emerged as a promising alternative to conventional semiconductors for their use in optoelectronic devices such as vertical photodiodes, offering a tuneable band gap and near-unity quantum efficiencies. They can be deposited with facile and diverse methods. The latest feat focused on reducing their defect density to minimise the noise and improve charge collection efficiencies. Yet the response times are limited by the devices' capacitance and, intrinsically, by the lifetime and transit time of the charge carriers. The capacitance limitation can be addressed only to a limited extent via the reduction of the active area of the photodiode, increasing in the meantime the fabrication complexity for comparable signal amplitudes. Alternative strategies focused on the intrinsic properties of semiconductors - such as exploiting the photo-Dember effect or engineering the defect-limited carrier lifetimes - elevated photodetectors to the femtosecond regime, and have yet to be considered for perovskite devices.<br/>In this study, we explored controlled photocurrent quenching through the introduction of selective recombination sites, to obtain fast, one-mm² perovskite photodiodes with response times beyond their capacitance limitations. By choosing suitable charge transport layers, and by offsetting the perovskite precursor stoichiometry, the density of interfacial recombination sites can be controllably increased, as highlighted through an in-depth study of photocurrent transients under picosecond laser pulses. The device photo-response is tuned to observe an isolated sharp signal with ns decay and a 3-dB drop at 15 MHz, enabling the resolution of distances in the cm-range using direct time-of-flight measurements. These results are a major leap towards the development of wavelength-selective, cost-effective, and fast perovskite photodetectors with improved photo-response for Light Detection and Ranging (LiDAR) applications. LIDAR sensors are of paramount importance in highly automated processes and for self-driving cars.