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Charge injection is known as the major source of dark current under an applied reverse bias, which directly influences the performance of organic photodetectors with diode architecture. However, it is unclear which of various contributions, such as electron flow through the junction, shunt leakage, thermionic emission, and tunnelling, are dominant. This study investigates the thermionic emission and tunneling models to describe the origin of experimentally measured dark current generated in an organic photodetector. To elucidate the dominant mechanism, the barrier energies at anodic contacts are set from 0.6 to 1.0 eV using photosensitive layers composed of different acceptors. A linear relation is found between the natural logarithm of the dark current density under reverse bias and the square root of the barrier height, which strongly suggests direct tunneling as dominant mechanism for dark current injection. This conclusion is strengthened by temperature dependent dark current analysis. Further knowledge of the dominant mechanism by charge injection can help devise an effective strategy to suppress dark current for effective organic photodetector device implementation. [ABSTRACT FROM AUTHOR]

In this study, a promising film formation technique is highlighted, named mold‐assisted decal‐coating, as a thin film transfer printing process using the polyurethane acrylate‐based stamping mold. By optimizing the surface energy of the mold with wetting coefficient theory, the mold‐assisted decal‐coating process is successfully demonstrated by transferring the photoactive layer composed of the polymer donor, poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b;4,5‐b′]dithiophene‐2,6‐diyl‐alt‐(4‐(2‐ethylhexyl)‐3‐fluorothieno[3,4‐b]thiophene‐)‐2‐carboxylate‐2‐6‐diyl)] and a narrow bandgap non‐fullerene acceptor (NFA), 2,2′‐[[4,4,9,9‐tetrakis(4‐hexylphenyl)‐4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene‐2,7‐diyl]bis[[4‐[(2‐ethylhexyl)oxy]‐5,2‐thiophenediyl]methylidyne(5,6‐difluoro‐3‐oxo‐1H‐indene‐2,1(3H)‐diylidene)]]bis[propanedinitrile]. This process induces a well‐ordered morphology of photoactive material, prevents damage to the underlying layer by suppressing the solvent penetration. Both photovoltaic cells and photodetectors prepared by the decal‐coated photoactive layers containing fluorinated NFAs showed higher performance (power conversion efficiency = 10.69% and specific detectivity = 1.27 × 1012 A cm Hz1/2 W−1, respectively) than those of cells prepared by the spin‐coating method owing to morphology inversion and smoother interface that led to suppressed internal resistance and enhanced charge flow in normal structure. Thus, the reproducible decal‐coating process using a customized elastomeric mediator is an important thin film coating technique for efficient next‐generation organic optoelectronic materials. [ABSTRACT FROM AUTHOR]

Herein, non‐fullerene acceptor‐based organic photodiodes are compared with fullerene acceptor‐based organic photodiodes. The non‐fullerene acceptor, ethylhexyl‐rhodanine‐benzothiadiazole‐coupled indacenodithiophene (eh‐IDTBR)‐based organic photodiodes show a higher detectivity (1.61 × 1013 cm Hz1/2 W−1) and a faster response time (≈2.7 µs) than the fullerene acceptor, [6,6]‐phenyl C71 butyric acid methyl ester (PC71BM)‐based organic photodiodes (3.25 × 1012 cm Hz1/2 W−1 and ≈6.24 µs, respectively) owing to the excellent dark current suppression of the carrier injection and the low trap density of eh‐IDTBR. Moreover, the eh‐IDTBR‐based photodetector shows better operational device stability than the fullerene counterpart under electrical and thermal stress. This is corroborated by the morphology and crystallography analyses, both of which reveal that the eh‐IDTBR‐containing photo‐sensitive films remain intact after imposing an external stress. This study elucidates important key advantages of the non‐fullerene acceptor, eh‐IDTBR, and sets a milestone as it compares the non‐fullerene acceptors and fullerene acceptors in organic photodiodes for the first time. This work sets a new record for the performance and stability of solution‐processable non‐fullerene acceptor‐based organic photodiodes. [ABSTRACT FROM AUTHOR]