While only few organic photodiodes have photoresponse spectrum past the silicon limit of 1.1 um, novel shortwave infrared (SWIR) polymers are emerging, and a better understanding of the limiting factors in narrow bandgap devices is critically needed to predict and advance performance. Based on state-of-the-art SWIR bulk heterojunction photodiodes that show spectral response up to 1.7 um, this work demonstrates a new model that properly accounts for the increasing electric-field dependence of photocurrent in narrow bandgap materials. This physical model offers an expedient method to pinpoint the origins of efficiency losses, by decoupling the exciton dissociation efficiency and charge collection efficiency in photocurrent-voltage measurements. Our results indicate that the main loss is due to poor exciton dissociation efficiency, particularly significant in photodiodes with low-energy charge-transfer states. The main reasons for low charge-transfer exciton dissociation efficiency and high noise will be discussed to give a better understanding on the differences of the device physics bewteen SWIR photodiode and those working in the visible. The optimal detectivity is obtained at zero external bias in photodiodes with film thicknesses &lt;= 350 nm for the bulk heterojunction. The measured results that include all noise components show a infrared peak detectivity of 5 x 10^<sup>10</sup> Jones with a spectral range up to 1.55 um. Several demonstrations are also conducted to show the various potential applications of organic SWIR photodiodes including distinguishing the heart pulse rate, quantifying the ethanol-water content in a mixture with 1% accuracy, and image reconstruction.

Detectivity of shortwave infrared organic photodiodes

255th National Meeting (2018)

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