Cavity Enhanced Organic Photodiodes with Charge Collection Narrowing

Abstract

Color discrimination in photodetection is conventionally achieved using broadband‐absorbing inorganic semiconductors with passive optical filters. Organic semiconductors show promise to deliver narrowband spectral responses due to their tunable optical properties. While achieving narrow‐absorbing organic semiconductors is an ongoing endeavor in the synthetic chemistry community, charge collection narrowing is introduced as a “material‐agnostic” technique to realize narrowband spectral responses using broadband absorbers such as blends of organic semiconductors, inorganic nanocrystals, and perovskites in a photodiode architecture. Charge collection narrowing in organic semiconductors demands photoactive junction thicknesses on the order of a few micrometers causing fabrication difficulties and limitations in device metrics such as frequency bandwidth. In this work it is shown that electrical inversion can result in charge collection narrowing in organic photodiodes with active layer thicknesses on the order of hundreds of nanometers and hence much easier to achieve via high throughput solution processing techniques. Additionally, it is shown that an indium tin oxide/gold electrode with modified work function acts as a cavity mirror, further narrowing the spectral response and at the same time delivering an extremely selective cathode, suppressing the dark current dramatically. Nearly voltage independent detectivities of 1013 Jones are achieved with an active sensing area of 0.2 cm2.

Recent Progress in Organic Photodetectors and their Applications

“…[91] Besides, a more promising strategy for OPDs with narrowband detection is to manipulate internal quantum efficiency via charge collection narrowing (CCN). [92,93] The working principle of CCN connects with the wavelength-dependent absorption coefficients of incident photons within the photoactive layer. According to Beer-Lambert law, photons with an energy matching the absorption peak of materials will be absorbed in the surface of the active layer.…”

Color‐Selective Printed Organic Photodiodes for Filterless Multichannel Visible Light Communication

“…Recently, solution-processed wavelength selective OPDs have been realized by means of: i) optical filtering, [5,22] ii) charge collection narrowing, [23][24][25] and iii) cavity enhanced absorption. [26][27][28] All of these techniques have demonstrated wavelength selective responsivity and enabled successful application in color reconstruction or IR-spectroscopy. However, all three approaches present challenges that limit their technological transfer toward industrially relevant printing techniques.…”

Narrowband organic photodetectors – towards miniaturized, spectroscopic sensing

“…This issue was circumvented by the same group by using inverted devices comprising unbalanced mobilities. 192 In this structure, only photons with energy close to the absorption onset generate holes that can be extracted, since they are close to the anode. Photons with energy above the optical gap generate slow holes close to the cathode.…”

“…With this approach, the thickness of the active layer was reduced to 700 nm, in contrast to the micrometer range previously required, and D* on the order of 10 13 Jones was demonstrated at 700 nm response wavelength. 192…”