Tuning Electronic and Morphological Properties for High‐Performance Wavelength‐Selective Organic Near‐Infrared Cavity Photodetectors

Abstract

Incorporation of compact spectroscopic near‐infrared (NIR) light detectors into various wearable and handheld devices opens up new applications, such as on‐the‐spot medical diagnostics. To extend beyond the detection window of silicon, i.e., past 1000 nm, organic semiconductors are highly attractive because of their tunable absorption. In particular, organic NIR wavelength‐selective detectors have been realized by incorporating donor:acceptor thin films, exhibiting weak intermolecular charge‐transfer (CT) absorption, into an optical microcavity architecture. In this work, the alkyl side chains of the well‐known PBTTT donor polymer are replaced by alkoxy substituents, hereby redshifting the CT absorption of the polymer:PC61BM blend. It is shown that the unique fullerene intercalation features of the PBTTT polymer are retained when half of the side chains are altered, hereby maximizing the polymer:fullerene interfacial area and thus the CT absorption strength. This is exploited to extend the detection range of organic narrow‐band photodetectors with a full‐width‐at‐half‐maximum of 30–38 nm to wavelengths between 840 and 1340 nm, yielding detectivities in the range of 5 × 1011 to 1.75 × 1010 Jones, despite the low CT state energy of 0.98 eV. The broad wavelength tuning range achieved using a single polymer:fullerene blend renders this system an ideal candidate for miniature NIR spectrophotometers.

A PDTPQx:PC61BM blend with pronounced charge-transfer absorption for organic resonant cavity photodetectors – direct arylation polymerization vs. Stille polycondensation

“…For all PDTPQx:PC61BM (1:4) based devices, an undulating surface was observed when monitoring the blend thickness with a profilometer. Future optimization of the blend surface morphology and homogeneity of the blend thickness, directly linked to the EQE and FWHM in an optical cavity OPD, 25 could possibly further enhance the detectivities.…”

“…5,6 One of these approaches is based on the integration of donor:acceptor thin films showing weak (but distinct) charge-transfer (CT) absorption into optical cavity devices. [22][23][24][25] Encouraging results have been achieved so far, but this has been limited to very few donor polymer backbones (notably PBTTT 23,25 ), presumably due to the requirement of intimate mixing between the donor and acceptor material on a molecular scale to achieve strong CT absorption. Alternative conjugated polymers showing higher highest occupied molecular orbital (HOMO) energy levels and intimate mixing with suitable acceptors -to shift the CT absorption wavelength further into the NIR and enhance the external quantum efficiency (EQE), respectively -should be investigated to elucidate the limits of this approach and to formulate clear material design guidelines.…”

“…The high-HOMO characteristic of PDTPQx is desired for its application in organic resonant cavity photodetectors, as this decreases the energy of the intermolecular CT absorption of the polymer:PC61BM blend, with a concomitant redshift of the direct CT absorption into the NIR. 6,[22][23][24][25] Therefore, the DArP PDTPQx:PC61BM blend is well suited to implement into a resonant optical cavity device architecture. Using this type of OPD, wavelength selective photodetection up to 1140 nm is achieved.…”

Ultraviolet Narrowband Photomultiplication Type Organic Photodetectors with Fabry−Pérot Resonator Architecture

“…Ultraviolet (UV) narrowband PM-OPDs can hardly be realized by solely employing CIN concept. Optical microcavity with a Fabry−Pérot (FP) resonator architecture is usually utilized to adjust light with specific wavelength, [19][20][21] which can be utilized to adjust spectral response range of PM-OPDs. The PM-OPDs coupled with optical microcavity (COM) should be a smart strategy to achieve UV highly narrowband response.…”

Self‐powered bifunctional perovskite photodetectors with both broadband and narrowband photoresponse

“…The light absorption property of PDs can be tuned via a variety of strategies, for example, by combining with optical bandpass filters, plasmonic-enhanced specific absorption, and optical microcavities. [6][7][8][9] The charge collection efficiency within a device can be modulated through, for example, a charge collection narrowing (CCN) mechanism by thickening the active layer or importing interfacial charge recombination. [9][10][11] Metal halide perovskites have demonstrated excellent performance in both BB and NB PDs, including a fast response speed, high responsivity, and highly tunable spectral responses.…”