interest in both academic and industrial landscapes for a wide range of applications, including image sensing, [8] optical communication, [9] environmental monitoring, and biomedical applications. [10,11] New emerging applications require selfpowered, cost-effective, highly sensitive, and flexible devices. [12][13][14] These conditions can be fully satisfied using PDs based on perovskite active layers, which combine high ambipolar charge carrier mobility [6,15] with long carrier diffusion length, [16,17] effective light absorption, [18] high defect tolerance [19,20] and low-cost solution processability, [21] making them suitable candidates for high-performance PDs.The route to obtain highly sensitive sensors requires minimizing dark current (J d ) values, which limits the noise (i n ) in devices and maximizes light conversion. To date, few methods exist to reduce the dark current in PDs. They are based on the use of charge-blocking layers to minimize charge injection. [22,23] Other strategies are related to inclusion of additives [24,25] or controlling film crystallization [26,27] to minimize backward charge injection at the electrodes. However, there is a deficit of efforts focused on understanding the role of perovskite composition and its correlation to device J d . Tuning halide composition in perovskites isa powerful approach demonstrated to enhance the performance of perovskite photovoltaic devices where such compositional modifications drive improvements in open-circuit voltage (V oc ) and a reduction in nonradiative voltage losses. Similarly, photodetectors (PDs) operate as light to current conversion devices hence it is relevant to investigate whether performance enhancements can be achieved by similar strategies. Herein, perovskite PDs are fabricated with an inverted photodiode configuration based on a MAPb(I 1-x Br x ) 3 perovskite (MA = methylammonium) active layer over the x = 0-0.25 composition range. Interestingly, it has been found that increasing the Br content up to 0.15 (15%) leads to a significant reduction in dark current (J d ), with values as low as 1.3 × 10 −9 A cm -2 being achieved alongside a specific detectivity of 8.7 × 10 12 Jones. Significantly, it has been observed an exponential relationship between the J d of devices and their V oc over the 0-15% Br range. The superior performances of the 15% Br-containing devices are attributed to the reduction of trap states, a better charge extraction of photogenerated carriers, and an improvement in photoactive layer morphology and crystallinity.

One of the key challenges facing organic photodiodes (OPDs) is increasing the detection into the infrared region. Organic semiconductor polymers provide a platform for tuning the bandgap and optoelectronic response to go beyond the traditional 1000-nanometer benchmark. In this work, we present a near-infrared (NIR) polymer with absorption up to 1500 nanometers. The polymer-based OPD delivers a high specific detectivity D * of 1.03 × 10 10 Jones (−2 volts) at 1200 nanometers and a dark current J d of just 2.3 × 10 −6 ampere per square centimeter at −2 volts. We demonstrate a strong improvement of all OPD metrics in the NIR region compared to previously reported NIR OPD due to the enhanced crystallinity and optimized energy alignment, which leads to reduced charge recombination. The high D * value in the 1100-to-1300-nanometer region is particularly promising for biosensing applications. We demonstrate the OPD as a pulse oximeter under NIR illumination, delivering heart rate and blood oxygen saturation readings in real time without signal amplification.