Highly sensitive, sub-microsecond polymer photodetectors for blood oxygen saturation testing

Abstract

Bottom surface of active layers and interface of indium tin oxide (ITO) electrodes and active layers play a crucial role in determining the performance of polymer photodetectors with photomultiplication (PM-PPDs). The interfacial trapped electron distribution closing to ITO electrodes will determine spectral response range and external quantum efficiency (EQE) of PM-PPDs. The bottom interface is more sensitive than top interface when light is coming from the ITO side, and the larger density of generated charge on the bottom interfaces will induce interfacial band more bending for efficient charge tunneling injection. Highly sensitive and sub-microsecond PM-PPDs are achieved with PMBBDT:Y6 (100:7, w/w) as active layers under forward bias, yielding EQE of 18,700% at 320 nm, 21,700% at 600 nm and 16,400% at 810 nm under a bias of 7 V, respectively, as well as fast response time of 79 μs. The high EQE of the PM-PPDs is attributed to efficient hole tunneling injection from ITO electrode under forward bias. The electron traps closing to ITO electrode will be quickly filled up when light is coming from ITO side, leading to interfacial band more bending for hole tunneling injection. Importantly, the PM-PPDs is performed to measure heart rate (HR) and blood oxygen saturation (SpO 2 ), and the measured data by the PM-PPDs are very similar with those obtained by commercial photodetectors.

Wide Bandgap Polymer with Narrow Photon Harvesting in Visible Light Range Enables Efficient Semitransparent Organic Photovoltaics

“…To further gain insight on charge transport properties in active layers with varied D18:N3 weight ratio, space charge limit current (SCLC) method was employed to investigate charge mobility in blend films. [38,39] The charge mobility in blend films depended on D18:N3 weight ratio are exhibited in Figure 3b. The details about single-carrier device fabrication and mobility calculation are displayed in the Supporting Information.…”

Recent progress in all-small-molecule organic photovoltaics

“…As the most popular central core unit used in small molecular donors, the benzo[1,2-b:4,5-b 0 ] dithiophene (BDT) unit possesses a symmetric and rigid planar conjugated structure, which benets the electron delocalization and p-p stacking in the solid state, thus leading to excellent charge transport in devices. [61][62][63][64] With continuous efforts on molecular design, BDTcentral core based small molecular donors have achieved remarkable advancements for preparing highly efficient SMPVs.…”

Self‐Powered Organic Photodetectors with High Detectivity for Near Infrared Light Detection Enabled by Dark Current Reduction

“…[9,10] In the pursuit of high photon currents, the majority of photovoltaic mode OPDs are based on bulk-heterojunction (BHJ) structures, which are fabricated by blend casting (BC) a solution of donor and acceptor. [11][12][13][14] In the blend films, phase separation originating from the different surface energies of donor and acceptor is formed, which strongly influences the device stability. [15,16] In addition, the unfavorable charge injection from the contacts into the semiconductor is severe due to simultaneous existence of both donor and acceptor components near the anode and cathode interfaces in BC device, which directly leads to a high dark current density (J d ) and thus low detectivity (D*).…”