NIR) spectral region, to estimate the ratio of oxyhemoglobin and deoxyhemoglobin in arterial blood. Transmission pulse oximeters restrict the sensing location to tissues that can be transilluminated, generally fingertips or ear lobes. To overcome this limitation, pulse oximeters should be used in reflective mode, [7] that is, sensing light that slightly penetrates in the tissue and is then reflected. This opens the possibility to monitor pulse rate and blood oxygenation beyond the traditional sensing locations (e.g., fingertip and earlob).Recent developments in the field of organic electronics have led to reflectance oximeters based on organic photodiodes (OPDs). [8][9][10][11] The potential for large-area manufacturing using industrially scalable coating techniques, [12] combined with the wide absorption spectrum and high color selectivity, [13] makes OPDs attractive for this class of optoelectronic sensors. Organic reflectance oximeters on light-weight flexible substrates [14] can easily adapt to complex shapes of the body, thereby potentially providing a versatile alternative to rigid conventional designs. Furthermore, the signal-to-noise ratio (SNR) of flexible oximeters is enhanced by the formation of a conformal sensor-skin interface with lower effective impedance, [15][16][17] which reduces the electronic noise during PPG acquisition. Lochner et al. [8] first combined organic light emitting diodes (OLEDs) with two OPD pixels in an all-organic pulse oximeter. This sensor successfully measured pulse rate and blood oxygenation level within an experimental error of 1% and 2%, respectively. In 2018, Khan et al. [9] presented a reflectance oximeter array composed of four red and four NIR OLEDs, and eight OPDs. Such configuration introduces the functionality of 2D oxygenation mapping capability. The sensor was used to measure oxygen saturation on the forehead with 1.1% error and to create 2D oxygenation maps of adult forearms under under normal and ischemic conditions.Here, we develop an NIR sensitive OPD array of 16 × 16 pixels and demonstrate its potential in reflectance PPG. Each OPD pixel exhibits NIR sensitivity up to ≈ 950 nm together with a low dark current density in the order of 10 −6 mA cm −2 . As the OPD array is operated in reflective mode, a thin semi-transparent top electrode in each pixel is needed not to hinder light that reaches the fingertip and is then reflected. At the same time, the top electrode must form a continuous layer to ensure low series resistance. To fulfill both requirements, we use a 10 nm Ag top electrode. Notably, we use opaque bottom electrodes in combination with the semi-transparent non-patterned top electrode, so that only reflected light is detected by the OPD array.Reflectance oximeters based on organic photodiode (OPD) arrays offer the potential to map blood pulsation and oxygenation via photoplethysmography (PPG) over a large area and beyond the traditional sensing locations. Here, an organic reflectance PPG array based on 16 × 16 OPD pixels is developed. The individual ...