Near-infrared organic photodetectors based on bay-annulated indigo showing broadband absorption and high detectivities up to 1.1 μm

Abstract

Near-infrared photodetection is valuable for numerous scientific, industrial and recreational applications. The implementation of organic semiconductors in near-infrared photodetectors offers additional advantages, such as printability on flexible substrates, reduced manufacturing costs and facile tuning of the detection range. In this work, the nature-inspired bay-annulated indigo (BAI) dye is employed as a building block for near-infrared sensitive, push-pull type conjugated polymers. The electron-deficient BAI moiety is copolymerized with a set of electron-rich monomers, affording polymers with an absorption onset up to 1300 nm and a sufficiently high lowest unoccupied molecular orbital, allowing electron transfer to standard fullerene acceptors. Bulk heterojunction type organic photodetectors are fabricated and the resulting device characteristics are analysed. The best performing photodetector is based on the polymer PTTBAI comprising thieno[3,2-b]thiophene as the electron-rich moiety. It has a superior light to dark current ratio, with a dark current density of 10 -7 A/cm², resulting in a (shot-noise limited) detectivity of 10 12 Jones at -2 V bias within the spectral window of 600−1100 nm, exceeding the detectivity of conventional silicon CCD photodetectors in the near-infrared region (~10 11 Jones).

Intrinsic Detectivity Limits of Organic Near‐Infrared Photodetectors

“…[ 15 ] Furthermore, the absorption window of organic active materials can be fine‐tuned via chemical modifications toward specific applications like bioimaging in the second NIR window (between 1000 and 1350 nm). [ 3,16 ] These advantages, as well as their non‐toxicity, make organic semiconductors a hot topic in the NIR photodetection field. [ 17 ] A dozen NIR photoactive organic materials have been reported to date, with only a minor fraction showing photodetection up to 1400 nm.…”

“…The synthesis and performance in NIR photodiodes of three of the used polymers—PTTBAI, PBTQ(OD), and PTTQ(HD)—have been reported before. [ 16,39 ] The synthesis route for the novel ultralow gap push–pull copolymer PTTQn(HD) is provided in the Supporting Information (Scheme S1, Supporting Information). The chemical structures and their frontier orbital energy levels, as estimated via cyclic voltammetry (CV, Figure S2, Supporting Information), are shown in Figure a–b, respectively.…”

Near‐infrared organic photoelectric materials for light‐harvesting systems: Organic photovoltaics and organic photodiodes

“…OPD devices fabricated by utilizing these new narrow‐band polymers blended with PC 71 BM demonstrated a D* value on the order of 10 11 Jones across the spectral window of 600 to 1430 nm together with a measurable D * up to 1800 nm (as shown in Figure ). In 2018, Verstraeten et al used the bay‐annulated indigo (BAI) monomer as an NIR‐sensitive building block to synthesize six different push‐pull type conjugated polymers (namely PCPDTBAI, PTBAI, PDTPBAI, PTTBAI, PTTPABI, and PDFBBAI as shown in Figure ) . These narrow‐band polymers possess a photoresponse edge of up to 1300 nm together with a sufficiently high LUMO level to provide adequate energetic driving force for charge transfer from the polymers to the fullerene acceptors.…”

Non-fullerene-based organic photodetectors for infrared communication

“…20 Despite years of development, the main limitation of using fullerene-based BHJ is, with a notable exception, 21 the low external quantum efficiency (EQE) in the infrared region (typically less than 30% at 900 nm). [22][23][24][25] Replacing fullerene by non-fullerene acceptors (NFAs) was an important milestone for OSCs. [26][27][28] If ultralow bandgap NFAs were originally developed to extend the absorption of the solar spectrum and thus give more current in a solar cell, they could also be used to specifically target IR radiation.…”