In phototransistors, the photovoltaic‐induced current is proportional to the turn‐on voltage shift and the total number of trapped charges. However, it is challenging to obtain a high turn‐on voltage shift simply by using minority carrier trap sites because high‐concentration carrier trap sites introduce strong current traps and carrier recombination. In this study, spatially separated, hole/electron, dual traps are introduced into a phototransistor, demonstrating the possibility of combining hole and electron traps without and with illumination, respectively, to obtain a large turn‐on voltage shift. The near‐infrared phototransistor demonstrates a high light‐to‐dark current ratio (1 × 106) alongside a turn‐on voltage shift of 28 V. The current quenching of the charge trap is effectively compensated by the threshold voltage shift, resulting in an increase of the drain–source current. The dual traps induce a low‐noise current and a high photoresponsivity (5.26 × 103 A W–1) under the same gate voltage (Vg = 0 V), exhibiting an ultrahigh detectivity (D1/f∗ = 1.88 × 1015 Jones; Dshot∗= 8.21 × 1016 Jones).
In organic photodetectors, photomultiplication is mainly originated from interfacial and/or bulk charge traps, which induces slow response due to the slow release of trapped charges and strongly limits the optimization of the overall performance. This study has exhibited a remarkable case that the gain (>1) and response speed of the lateral photodetectors are promoted simultaneously and effectively by increasing the trap ratio. For lateral photodetectors with silver nanoparticles and PDPPBTT:PC 61 BM bulk heterojunction, the gain increases from 12.7 to 19.8 and the fall time decreases from 313.4 to 172.9 ms as the PC 61 BM ratio increases from 5:1 to 1:1. The lateral photodetector structure with a long electrode distance has been testified to play the key role for simultaneous promotion compared with vertical photodiodes, allowing the charges to trap well in the PC 61 BM-rich phase at a high PC 61 BM ratio and accumulation of multiple built-in electric fields. The long channel distance and silver nanoparticles also effectively restrain the increment of dark current with PC 61 BM loading, resulting in a high detectivity of 1.7 × 10 12 Jones under 0.031 mW cm −2 @ 820 nm. It is of great theoretical and practical value for the high-performance photodetectors with simultaneous high photomultiplication and quick response.
High-resolution
organic light-emitting diode (OLED) display industries
are in significant demand for organic light-emitting materials of
narrow-band emission. However, current organic light-emitting materials,
especially the orange–red luminophores, usually exhibit broad
emission as a result of the large structural relaxation as well as
vigorous vibronic couplings in the excited state. In this study, a
novel molecule, 2,2′-(7-phenylquinolino[3,2,1-de]acridine-5,9-diylidene)dimalononitrile (QADMA-Ph), with methylenemalononitrile
as the acceptor and acridine as the donor, is designed and synthesized.
According to the analysis of photophysical properties and theoretical
computation, we found that the strong intramolecular charge transfer
character endows QADMA-Ph with a favorable bandgap to the orange–red
emission region. Benefiting from the confined π conjugation
of the acceptor and donor within the locked-in and nonplanar structure,
the excited state of QADMA-Ph presents dominant low-frequency vibronic
coupling arising from the twisting vibration of the nonplanar core
and the rotating vibration of the peripheral substituent. Consequently,
QADMA-Ph exhibits a narrow-band emission at 568 nm with a full width
at half maximum (fwhm) of 41 nm/0.13 eV in the diluted toluene solution.
The corresponding OLED emitted a narrow electroluminescence at 592
nm with a fwhm of 54 nm/0.19 eV.
In phototransistors with bulk heterojunction, long conductive channels with tens-micrometers length supply the discontinuous phase morphology and unbalance charge transport, resulting in an obvious storage of photoinduced charges, however, the...
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