Abstract
The high binding energy and low diffusion length of photogenerated Frenkel excitons have long been viewed as major drawbacks of organic semiconductors. Therefore, bulk heterojunction structure has been widely adopted to assist exciton dissociation in organic photon-electron conversion devices. Here, we demonstrate that these intrinsically “poor” properties of Frenkel excitons, in fact, offer great opportunities to achieve self-filtering narrowband organic photodetectors with the help of a hierarchical device structure to intentionally manipulate the dissociation of Frenkel excitons. With this strategy, filter-free narrowband organic photodetector centered at 860 nm with full-width-at-half-maximum of around 50 nm, peak external quantum efficiency around 65% and peak specific detectivity over 1013 Jones are obtained, which is one the best performed no-gain type narrowband organic photodetectors ever reported and comparable to commercialized silicon photodetectors. This novel device structure along with its design concept may help create low cost and reliable narrowband organic photodetectors for practical applications.
Highlights
The high binding energy and low diffusion length of photogenerated Frenkel excitons have long been viewed as major drawbacks of organic semiconductors
The no-gain type narrowband detectors enabled by collection narrowing (CCN) concept modulate the external quantum efficiency (EQE) spectrum by manipulating the collection efficiency of free charges at the corresponding electrodes
By calculating the diffusion length and the distribution of the photogenerated excitons in the donor layer, we could intentionally manipulate the dissociation efficiency of excitons generated by various wavelengths of incident light via a hierarchical device structure
Summary
The high binding energy and low diffusion length of photogenerated Frenkel excitons have long been viewed as major drawbacks of organic semiconductors. We demonstrate that these intrinsically “poor” properties of Frenkel excitons, offer great opportunities to achieve self-filtering narrowband organic photodetectors with the help of a hierarchical device structure to intentionally manipulate the dissociation of Frenkel excitons With this strategy, filter-free narrowband organic photodetector centered at 860 nm with full-width-at-half-maximum of around 50 nm, peak external quantum efficiency around 65% and peak specific detectivity over 1013 Jones are obtained, which is one the best performed no-gain type narrowband organic photodetectors ever reported and comparable to commercialized silicon photodetectors. Unlike its inorganic counterparts, when an organic semiconductor absorbs a photon, a localized Frenkel exciton is created due to the weak intermolecular van der Waals interaction alongside with the low dielectric constant[19,20] This exciton cannot spontaneously separate into free charge due to the strong Coulombic interaction[21], and the short lifespan of exciton limits its diffusion length within tens of nanometers[22]. It was interestingly found that this novel methodology can efficiently suppress the response outside the detection window while retaining high sensitivity in the detection region, which enabled us to produce a series of simple structure visible-blind near-infrared (NIR) narrowband OPDs with outstanding performances
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