Near‐infrared organic photodetectors (NIR OPDs) comprising ultra‐narrow bandgap non‐fullerene acceptors (NFA, over 1000 nm) typically exhibit high dark current density under applied reverse bias. Therefore, suppression of dark current density is crucial to achieve high‐performance of such NIR OPDs. Herein, cyano (CN) with a strong electron‐withdrawing property is introduced into alkoxy thiophene as a π‐bridge to adjust its optoelectronic characteristics, and the correlation between dark current density and charge injection barrier is investigated. Compared with their motivated NFA (COTH), the novel CN‐substituted NFAs, COTCN and COTCN2, exhibited deeper‐lying highest occupied molecular orbital energy levels and narrower optical bandgap (<1.10 eV), owing to the strong inductive and resonance effect of CN. The dark current and total noise currents are minimized as the number of substituted CN increases because of the larger hole injection barrier. Consequently, PTB7‐Th:COTCN2 exhibited the best shot‐noise limited detectivity (D^*_sh, 1.18 × 10¹² Jones) and total noise detectivity (D^*_n, 1.33 × 10¹¹ Jones) compared with those of PTB7‐Th:COTH (D^*_sh, 2.47 × 10¹¹ Jones and D^*_n, 1.96 × 10¹⁰ Jones).

Organic photodetectors (OPDs) based on non‐fullerene acceptors (NFAs) have received considerable attention because of their potential for use in various commercial applications as near‐infrared (NIR) light sensing platforms. However, recent OPDs suffer from low NIR photoresponse and large dark/noise currents with narrow bandgap organic photoactive materials. Herein, a π‐bridge molecular engineering strategy replacing alkoxythienyl with benzothiadiazole for ultra‐narrow bandgap (ultra‐NBG) NFAs is designed to achieve simultaneously high photoresponse at NIR region and low noise current density, thereby leading to excellent NIR (≈1050 nm) detectivity (D^*). The newly synthesized ultra‐NBG NFAs, namely COB and CBT with optical bandgaps below 1.14 eV, present high responsivity (R) with 0.369 and 0.080 A W⁻¹, respectively, at a wavelength of 1050 nm. Especially, with effectively suppressed noise current density, COB‐based OPD exhibits a high NIR (≈1050 nm) D^* value of 2.18 × 10¹¹ cm Hz^1/2 W⁻¹ at −0.5 V bias. The obtained R and D^* values for these NFAs exceed or are comparable to those of a commercial Si photodetector at 1050 nm. This work provides important insight into the π‐bridge molecular engineering strategy for ultra‐NBG NFAs, which facilitate achieving highly sensitive NIR OPDs with high NIR photoresponse and low dark/noise current.

Owing to the development of highly efficient donor and non-fullerene small-molecule acceptor materials, the power conversion efficiency (PCE) of organic solar cells (OSCs) has reached 17–19%. However, most of the highest-efficiency OSC devices still use a toxic halogen solvent in their device fabrication process, which dilutes their potential for scale-up production. In this study, we report a terpolymer strategy to develop donor polymers via an eco-friendly process by controlling the aggregation behavior. By introducing ethyl thiophene-3-carboxylate (ET) into the molecular structure of D18, the consequential solubility is improved significantly enough for dissolution in eco-compatible solvents, while preserving adequate aggregation. As a result, the newly developed terpolymers (P_Ds) can be processed with an eco-compatible solvent, o-xylene, and an OSC consisting of a P_D with 10 mol% ET and Y6-BO exhibits an outstanding PCE of 15.5%, without any treatments such as additive addition, solvent vapor annealing, or thermal annealing. This excellent OSC performance is attributed to the superior charge carrier mobility, suppressed trap-assisted recombination, and substantial semi-crystalline behavior of the o-xylene processed PBET10:Y6-BO blend films. In addition, our o-xylene-based device shows a very good thermal stability of 90% retention of the initial PCE for 300 h in a 100 °C environment.

In this study, we explore an innovative approach to enhancing the photovoltaic performance of organic solar cells through core fluorination of the non‐fullerene acceptor. We developed a benzotriazole‐based non‐fullerene acceptor with a trifluorinated phenyl side chain, referred to as YNPF3, which has a significant impact on the molecular properties, including a surprisingly varied local dipole moment and crystalline nature, as well as effectively stabilizing the frontier molecular orbital energy levels. Furthermore, a trifluoro‐phenyl‐based non‐fullerene acceptor exhibits enhanced absorptivity, restricted voltage loss, and favorable photoactive morphology compared with its methyl side chain counterpart non‐fullerene acceptor. Consequently, a binary organic solar cell based on YNPF3 achieves an outstanding power conversion efficiency of 19.2%, surpassing the control device with a efficiency of 16.5%. Finally, the YNPF3‐based organic solar cell presents an impressive power conversion efficiency of 16.6% in a mini‐module device with an aperture size of 12.5 cm², marking the highest reported efficiency for series‐connected binary organic solar cells with a photoactive area over 10 cm².

The development of portable X‐ray detectors is necessary for diagnosing fractures in unconscious patients in emergency situations. However, this is quite challenging because of the heavy weight of the scintillator and silicon photodetectors. The weight and thickness of X‐ray detectors can be reduced by replacing the silicon layer with an organic photodetectors. This study presents a novel bithienopyrroledione‐based polymer donor that exhibits excellent photodetection properties even in a thick photoactive layer (~700 nm), owing to the symmetric backbone and highly soluble molecular structure of bithienopyrroledione. The ability of bithienopyrroledione‐based polymer donor to strongly suppress the dark current density (J_d ~ 10⁻¹⁰ A cm⁻²) at a negative bias (−2.0 V) while maintaining high responsivity (R = 0.29 A W⁻¹) even at a thickness of 700 nm results in a maximum shot‐noise‐limited specific detectivity of D_sh* = 2.18 × 10¹³ Jones in the organic photodetectors. Printed organic photodetectors are developed by slot‐die coating for use in X‐ray detectors, which exhibit D_sh* = 2.73 × 10¹² Jones with clear rising (0.26 s) and falling (0.29 s) response times upon X‐ray irradiation. Detection reliability is also proven by linear response of the X‐ray detector, and the X‐ray detection limit is 3 mA.