Broadband photomultiplication-type polymer photodetectors and its application in light-controlled circuit

Dual-Band Photomultiplication-Type Organic Photodetectors with Ultrahigh Signal-to-Noise Ratios

A series of dual-band photomultiplication (PM)-type organic photodetectors (OPDs) were fabricated by employing a donor(s)/acceptor (100:1, wt/wt) mixed layer and an ultrathin Y6 layer as the active layers, as well as by using PNDIT-F3N as an interfacial layer near the indium tin oxide (ITO) electrode. The dual-band PM-type OPDs exhibit the response range of 330-650 nm under forward bias and the response range of 650-850 nm under reverse bias. The tunable spectral response range of dual-band PM-type OPDs under forward or reverse bias can be explained well from the trapped electron distribution near the electrodes. The dark current density (JD) of the dual-band PM-type OPDs can be efficiently suppressed by employing PNDIT-F3N as the anode interfacial layer and the special active layers with hole-only transport characteristics. The light current density (JL) of the dual-band PM-type OPDs can be slightly increased by incorporating wide-bandgap polymer P-TPDs with relatively large hole mobility (μh) in the active layers. The signal-to-noise ratios of the optimized dual-band PM-type OPDs reach 100,980 under -50 V bias and white light illumination with an intensity of 1.0 mW·cm-2, benefiting from the ultralow JD by employing wide-bandgap PNDIT-F3N as the anode interfacial buffer layer and the increased JL by incorporating appropriate P-TPD in the active layers.

PC71BM as Morphology Regulator for Highly Efficient Ternary Organic Solar Cells with Bulk Heterojunction or Layer-by-Layer Configuration

The ternary strategy is one of the effective methods to regulate the morphology of the active layer in organic solar cells (OSCs). In this work, the ternary OSCs with bulk heterojunction (BHJ) or layer-by-layer (LbL) active layers are prepared by using the polymer donor PM6 and the non-fullerene acceptor L8-BO as the main system and the fullerene acceptor PC71BM as the third component. The power conversion efficiencies (PCEs) of BHJ OSCs and LbL OSCs are increased from 17.10% to 18.02% and from 17.20% to 18.20% by introducing PC71BM into the binary active layer, respectively. The in situ UV-vis absorption spectra indicate that the molecular aggregation and crystallization process can be prolonged by introducing PC71BM into the PM6:L8-BO or PM6/L8-BO active layer. The molecular orientation and molecular crystallinity in the active layer are optimized by introducing the PC71BM into the binary BHJ or LbL active layers, which can be confirmed by the experimental results of grazing incidence wide-angle X-ray scattering. This study demonstrates that the third component PC71BM can be used as a morphology regulator to regulate the morphology of BHJ or LbL active layers, thus effectively improving the performance of BHJ and LbL OSCs.

Plasmonic-Enhanced Tunable Near-Infrared Photoresponse for Narrowband Organic Photodetectors

Near-infrared (NIR) narrowband organic photodetectors (OPDs) can be essential building blocks for emerging applications including wireless optical communication and light detection, but further improvement of their performances remains to be a great challenge. Herein, a light manipulation strategy combining solution-processable gold nanorings (AuNRs)-based hole transporting layer (HTL) and an optical microcavity is proposed to achieve high-performance NIR narrowband OPDs. Optical microcavities with a Fabry-Pérot resonator structure, guided by theoretical simulation, are coupled with PM6:BTP-eC9-based OPDs to exhibit highly tunable NIR selectivity. The further integration of AuNRs array with NIR-customized localized surface plasmon resonance in the HTL of the NIR narrowband OPDs enables evident NIR absorption enhancement, yielding a specific detectivity exceeding 1013 Jones (1.5 × 1012 Jones, calculated from noise spectral density) at 820 nm, along with a finely selective photoresponse (full width at half-maximum of 80 nm) and a 3-fold increase in photocurrent intensity. Finally, the practical application of our OPDs is demonstrated in an NIR communication system. These results reveal the great potential of an appropriate optical design for developing highly performing NIR narrowband OPDs.

The State-of-the-Art Solution-Processed Single Component Organic Photodetectors Achieved by Strong Quenching of Intermolecular Emissive State and High Quadrupole Moment in Non-Fullerene Acceptors

A bulk-heterojunction (BHJ) blend is commonly used as the photoactive layer in organic photodetectors (OPDs) to utilize the donor (D)/acceptor (A) interfacial energetic offset for exciton dissociation. However, this strategy often complicates optimization procedures, raising serious concerns over device processability, reproducibility, and stability. Herein, highly efficient OPDs fabricated with single-component organic semiconductors are demonstrated via solution-processing. The non-fullerene acceptors (NFAs) with strong intrinsic D/A character are used as the photoactive layer, where the emissive intermolecular charge transfer excitonic (CTE) states are formed within <1 ps, and efficient photocurrent generation is achieved via strong quenching of these CTE states by reverse bias. Y6 and IT-4F-based OPDs show excellent OPD performances, low dark current density (≈10-9 A cm-2 ), high responsivity (≥0.15 A W-1 ), high specific detectivity (>1012 Jones), and fast photo-response time (<10 µs), comparable to the state-of-the-art BHJ OPDs. Together with strong CTE state quenching by electric field, these excellent OPD performances are also attributed to the high quadrupole moments of NFA molecules, which can lead to large interfacial energetic offset for efficient CTE dissociation. This work opens a new way to realize efficient OPDs using single-component systems via solution-processing and provides important molecular design rules.

Flexible all-organic photodetectors via universal water-assisted transfer printing

Transfer printing of small-molecular organic semiconductors often faces challenges due to surface adhesion mismatch. Here, we developed a sacrificing-layer-assisted transfer printing technique for the deposition of small-molecular thin films. High-boiling-point ethylene glycol (EG) was doped in aqueous solution poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the sacrificing layer to manipulate residual water in film, which allowed chlorobenzene solution to spontaneously spread and form uniform film. The residual water guaranteed film delamination from the stamp, allowing for its transfer onto various substrates and seeding layers. As a proof of concept, laterally conductive organic photodetectors using recyclable EG-PEDOT:PSS electrodes and a small-molecular active layer were consecutively fabricated via transfer printing in ambient air. The resulting device exhibited a high on/off ratio of 711 and a fast rise time of 0.5 ms. Notably, the polymer electrode and the bulk heterojunction demonstrated unique repairability and recyclability.

Theoretical designing of non-fullerene derived organic heterocyclic compounds with enhanced nonlinear optical amplitude: a DFT based prediction

In current era, non-fullerene (NF) chromophores have been reported as significant NLO materials due to promising optoelectronic properties. Therefore, a series of NF based chromophores abbreviated as TPBD2-TPBD6 with D–π–A architecture was designed from the reference compound (TPBR1) by its structural tailoring with an efficient donor and various acceptor groups for the first time. First, the structures of said compounds were optimized at M06-2X/6-311G (d,p) level. Further, the optimized structures were utilized to execute frontier molecular orbitals (FMOs), UV–Visible (UV–Vis) absorption, density of states (DOS) and transition density matrix (TDM) analyses at the same level to understand the non-linear (NLO) response of TPBR1 and TPBD2-TPBD6. Promising NLO results were achieved for all derivatives i.e., the highest amplitude of linear polarizability ⟨α⟩, first (βtotal) and second ($$\gamma$$ γ total) hyperpolarizabilities than their parent molecule. The compound TPBD3 was noted with the most significant NLO properties as compared to the standard molecule. The structural modeling approach by utilizing the acceptor molecules has played a prominent role in attaining favorable NLO responses in the molecules. Thus, our study has tempted the experimentalists to synthesize the proposed NLO materials for the modern optoelectronic high-tech applications.

Geometric Structure, Electronic, and Spectral Properties of Metal-free Phthalocyanine under the External Electric Fields

Here, the ground-state structures, electronic structures, polarizability, and spectral properties of metal-free phthalocyanine (H₂Pc) under different external electric fields (EEFs) are investigated. The results show that EEF has an ultrastrong regulation effect on various aspects of H₂Pc; the geometric structures, electronic properties, polarizability, and spectral properties are strongly sensitive to the EEF. In particular, an EEF of 0.025 a.u. is an important control point: an EEF of 0.025 a.u. will bend the benzene ring subunits to the positive and negative x directions of the planar molecule. Flipping the EEF from positive (0.025 a.u.) to negative (-0.025 a.u.) flips also the bending direction of benzene ring subunits. The H₂Pc shows different dipole moments projecting an opposite direction along the x direction (-84 and 84 Debye for EEFs of -0.025 and 0.025 a.u., respectively) under negative and positive EEF, revealing a significant dipole moment transformation. Furthermore, when the EEF is removed, the molecule can be restored to the planar structure. The transformation of the H₂Pc structure can be induced by the EEF, which has potential applications in the molecular devices such as molecular switches or molecular forceps. EEF lowers total energy and reduces highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap; especially, an EEF of 0.025 a.u. can reduce the HOMO-LUMO gap from 2.1 eV (in the absence of EEF) to 0.37 eV, and thus, it can enhance the molecular conductivity. The first hyperpolarizability of H₂Pc is 0 in the absence of EEF; remarkably, an EEF of 0.025 a.u. can enhance the first hyperpolarizability up to 15,578 a.u. Therefore, H₂Pc under the EEF could be introduced as a promising innovative nonlinear optical (NLO) nanomaterial such as NLO switches. The strong EEF (0.025 a.u.) causes a large number of new absorption peaks in IR and Raman spectra and causes the redshift of electronic absorption spectra. The changes of EEF can be used to regulate the structure transformation and properties of H₂Pc, which can promote the application of H₂Pc in nanometer fields such as molecular devices.

Double-Layered Strategy for Broadband Photomultiplication-Type Organic Photodetectors and Achieving Narrowband Response in Violet, Red, and Near-Infrared Light

Broadband photomultiplication-type organic photodetectors (PM-OPDs) were prepared with PMBBDT:PY3Se-2V (1:1, wt/wt) as the absorbing layer (AL) and PC₇₁BM:P3HT (100:5, wt/wt) as the photomultiplication layer (PML) on the basis of the sandwich structure. The incident photons from ultraviolet light to the near-infrared region can be harvested by AL. The rather less P3HT in PML can produce plenty of isolated hole traps with P3HT surrounded by PC₇₁BM; the electron tunneling injection induced by trapped holes near the Ag electrode can lead to the photomultiplication (PM) phenomenon. The performance of PM-OPDs can be effectively improved by optimizing the AL thickness. The optimal PM-OPDs exhibit a broad spectral response from 300 to 1050 nm as well as an external quantum efficiency (EQE) of 5800% at 340 nm at 10 V bias, along with a specific detectivity (D*) of 3.78 × 10¹³ Jones. The spectral response of PM-OPDs is controlled by the trapped-hole distribution near the Ag electrode, primarily originating from the photogenerated holes in AL. To further optimize the spectral response of PM-OPDs, the optical filter layer (OFL) was used to manipulate light field distribution in AL. The violet, red, and near-infrared-light PM-OPDs were developed by employing different OFLs.

Improving the Efficiency of Organic Solar Cells with Methionine as Electron Transport Layer

Interface modification is an important way to get better performance from organic solar cells (OSCs). A natural biomolecular material methionine was successfully applied as the electron transport layer (ETL) to the inverted OSCs in this work. A series of optical, morphological, and electrical characterizations of thin films and devices were used to analyze the surface modification effects of methionine on zinc oxide (ZnO). The analysis results show that the surface modification of ZnO with methionine can cause significantly reduced surface defects for ZnO, optimized surface morphology of ZnO, improved compatibility between ETL and the active layer, better-matched energy levels between ETL and the acceptor, reduced interface resistance, reduced charge recombination, and enhanced charge transport and collection. The power conversion efficiency (PCE) of OSCs based on PM6:BTP-ec9 was improved to 15.34% from 14.25% by modifying ZnO with methionine. This work shows the great application potential of natural biomolecule methionine in OSCs.