Spiro‐Conjugation in Narrow‐Bandgap Nonfullerene Acceptors Enables Broader Spectral Response and Higher Detectivity for Near‐Infrared Organic Photodetectors

Abstract

Near‐infrared (NIR) organic photodetectors (OPDs) are competitive candidates for flexible electronics in biomedical imaging and optical communications applications. However, current OPDs still suffer from a low detectivity beyond 1000 nm and a high dark current at bias due to the lack of high‐performance narrow‐bandgap non‐fullerene acceptors (NFAs). In this study, spiro‐conjugated core donor (D) unit is adopted to construct NFAs, SPT‐4F and tSPT‐4F. Comparing with PT‐4F without spiro‐conjugation, the orthogonal spiro‐conjugated planes endow SPT‐4F and tSPT‐4F with more rigid conformation and thus superior intermolecular stacking, resulting in the enhanced absorption beyond 1000 nm. Impressively, tSPT‐4F based device gives the best performance with a dark current of 4.52 × 10−10 A cm−2 under reversed bias of −0.1 V, an external quantum efficiency (EQE) response over 48% at 1010 nm, a detectivity of 1.25 × 1013 Jones and a responsibility of 0.40 A W−1 at 1010 nm. To the best of the authors' knowledge, this is one of the best performed devices reported to date for binary NIR OPDs with response beyond 1000 nm. This study provides a feasible molecular design strategy to develop narrow‐bandgap NFAs with spiro‐conjugation for highly detective NIR OPDs.

Near-Infrared Organic Photodetectors with Spectral Response over 1200 nm Adopting a Thieno[3,4-c]thiadiazole-Based Acceptor

“…This is in agreement with our previous discussion for the thick-film devices that the J d level is governed by intrinsic BHJ properties and not shunt leakage paths. Eventually, a good D* of 1.1 (±0.2) × 10 11 Jones is achieved at a wavelength of 1200 nm under a modulation frequency of 10 4 Hz and a bias of −0.5 V as shown in Figure 5b.…”

“…Additionally, a R of ∼0.074 A W −1 at 1200 nm could be maintained. A good D* over 1 × 10 11 Jones is achieved at a wavelength of 1200 nm, working under a bias of −0.5 V and a modulation frequency of 10 4 Hz. Compared with the reported sub-silicon-band gap OPDs in the last 5 years, TTD(DTC-2FIC) 2 -based OPDs represent one of the few that can maintain a decent R and D* at 1200 nm, as shown in Table S1.…”

“…Organic semiconductors, on the other hand, are considered promising candidates due to their wet-chemistry synthesis, intrinsic softness, and low processing temperature. Benefiting from the development of non-fullerene small molecule acceptors (SMAs), NIR organic photodetectors (OPDs) have achieved comparable performance to silicon PDs. − To date, most high-performance NIR SMAs developed for OPDs incorporate an A–D–A (A for acceptor, D for donor) structure, with A being electron-withdrawing 2-(3-oxo-2,3-dihydro-1 H -inden-1-ylidene)­malononitrile derivatives. − These SMAs seldom show spectral response beyond that of silicon PDs (1100 nm), even fewer of high sensitivity ones. Recently, by designing a very strong electron-withdrawing quinoidal end group, Lin’s group successfully developed a new A–D–A structured SMA, L2, with specific detectivity ( D *) over 10 12 Jones up to 1.2 μm under zero bias …”

B─N Covalent Bond‐Based Nonfullerene Electron Acceptors for Efficient Organic Solar Cells

“…The rational design of conjugated backbones has been a major topic in the field of organic electronics, aiming to optimize light harvesting, frontier molecular orbital alignment, and charge transport. [2,[28][29][30][31][32][33] The introduction of heteroatoms into the conjugated skeleton is a very effective strategy to adjust the electronic structure of 𝜋-conjugated molecules. [34][35][36][37] BN heterocycles, compared to carbonaceous counterparts, demonstrate unique electronic properties owing to their different 𝜋-electron distributions and dipole moments, making them highly promising for organic optoelectronic materials.…”

Shortwave Infrared Organic Photodiodes Realized by Polaron Engineering

“…Hence, the development of SWIR photodetectors using organic materials is expected to facilitate significant advancements in the SWIR imaging industry. [13][14][15] In organic semiconductors, the low-energy absorption characteristics are typically realized using a donor-acceptor (DA) DOI: 10.1002/adma.202310250 push-pull-type copolymer approach, in which complex states of intramolecular charge transfer are utilized for narrowing the bandgap. [16,17] DA-type copolymer semiconductors with high molecular weights have been developed to realize a narrow bandgap and, consequently, a long-wavelength absorption.…”