Vacuum‐Processed Small Molecule Organic Photodetectors with Low Dark Current Density and Strong Response to Near‐Infrared Wavelength

Abstract

A near‐infrared photodetector with optimized performance is reported using varied thickness (20, 40, 60, and 80 nm) of the active layer comprising chloroaluminium phthalocyanine (ClAlPc) and fullerene (C70) at the ratio of 1:3, and TAPC:10% MoO3 and BPhen as electron and hole blocking layers, respectively. The experimental results reveal that the photodetector with 80 nm thick active layer provides the best performance at the wavelength of 730 nm achieving a very low dark current density of 1.15 × 10−9 A cm−2 and an external quantum efficiency of 74.6% with a responsivity of 0.439 A W−1 at −2 V bias. Additionally, the device exhibits a dramatic high detectivity of 4.14 × 1013 cm Hz1/2 W−1 at 0 V bias. The device exhibits not only a large linear response over a wide optical power range (LDR of 173.0 dB), but also a broad frequency response (778.7 kHz) and rise/fall time of 2.13/0.77 µs (based on trigger pulses at a frequency of 10 kHz) at the applied bias of −2 V. Based on the impedance spectroscopic study and the conventional characterization of electro‐optical properties, the results demonstrate the superiority of this device over other small molecule‐based near‐infrared photodetectors.

Highly Responsive and Thermally Reliable Near‐Infrared Organic Photodiodes Utilizing Naphthalocyanine Molecules Tuned with Axial Ligands

“…[7,9] Nonetheless, recent efforts have led to significant boosts in the performance of NIR OPDs using either polymers [10][11][12][13] or small molecule materials. [14][15][16][17][18][19] For instance, Xiong et al investigated solutionprocessed polymer NIR OPDs with PMDPP3T:PC 61 BM bulk heterojunction (BHJ), exhibiting a low dark current density (J d ) of 3.0 nA cm −2 at −0.2 V and a high external quantum efficiency (EQE) of 48% at 850 nm (a responsivity of 0.37 A W −1 ) for broad sensing applications. [11] A further improvement on the device performance has been recently made by introducing a very thick active layer (≈300 nm) with a non-fullerene acceptor (PTB7-Th:CO1-4Cl), achieving a high EQE of 66% at 960 nm (0.5 A W −1 ), a low J d of 7 nA cm −2 at −2 V, and a detectivity around 10 12 Jones.…”

“…[12] On the other hand, small moleculebased OPDs have also shown promising results, particularly featuring selective response to NIR wavelengths, which are mostly based on porphyrin, [14] squaraine, [15] and phthalocyanine (Pc). [16][17][18][19] Among the molecules, Pc-based NIR photodetectors have recently revealed the outstanding device performance. For example, the OPD with NIR-selective chloroindum Pc in the active layer resulted in a high EQE of 80% at 705 nm, a low J d of 10 nA cm −2 , and a detectivity over 10 12 Jones.…”

“…[17] The Pcbased NIR OPDs have been further developed by utilizing chloroaluminum Pc. Lee et al demonstrated a high EQE of 74.6% at 730 nm (0.439 A W −1 ), a very low J d of 1.15 nA cm −2 at −2 V bias, and a high detectivity over 10 13 Jones at 0 V bias, [19] indicative of the effectiveness of organic small molecules as potential NIR photodetector applications. However, these state-of-the-art results still have limited peak responses below 750 nm.…”

Vacuum‐Deposited Transparent Organic Photovoltaics for Efficiently Harvesting Selective Ultraviolet and Near‐Infrared Solar Energy

“…[ 19 ] In addition, we also found that ClAlPc blended with C 70 as an active layer can achieve dark current density <1 nA cm −2 and specific detectivity >4 × 10 13 cm Hz 1/2 W −1 at 730 nm, which might significantly improve the photoresponse property of the organic detectors. [ 21 ] Moreover, ClAlPc shows a high absorption coefficient to cover the UV/NIR region selectively and possess a low highest occupied molecular orbital level to increase the open‐circuit voltage ( V oc ) >0.7 V for OPVs. [ 55 ] In this article, we propose a new approach that uses bulk heterojunction (BH) of ClAlPc:C 60 as the active layer to modify the absorption profile and optical distribution in the device.…”

“…Therefore, these results not only demonstrate the vacuum‐deposited TPV with the highest AVT's value but also provide a route to fabricate transparent electrode consisting of Cu:Ag metal alloy and capping layer of WO 3 . It is worthwhile to mention that the ultrathin ClAlPc:C 60 active layer shows UV/NIR abosrption ability, which is advanageous for developing a novel light‐sensing or absorption electronics, such as NIR sensitive organic photovoltaics (OPVs), [ 19 ] semi‐TPVs, [ 8 ] multitandem OPVs, [ 20 ] wide‐absorption range organic photodetector, [ 21 ] organic upconversion devices, [ 22 ] etc. On the other hand, to further investigate the optical effect on our proposed TPV, we have used optical modeling to optimize each layer, i.e., organic active layer and transparent electrode for higher transmittance and lower reflection of lights in the devices.…”