High-Performance Flexible Near-Infrared-II Phototransistor Realized by Combining the Optimized Charge-Transfer-Complex/Organic Heterojunction Active Layer and Gold Nanoparticle Modification

In this article, a high-performance flexible near-infrared-II phototransistor (NIR-II PT) based on the charge-transfer-complex (CTC)/organic planar heterojunction and the gold nanoparticles (Au-NPs) modification has been designed and fabricated. The effects of the different stacking sequences of the CTC/organic layers on the device performances were studied, and the best CTC-based PT structure was obtained. The devices were further significantly improved by the modification of the Au-NPs layer. Compared with the devices on the rigid substrate, the devices prepared on the flexible substrate have better performances. It has been shown that this may be attributed to the better adhesion and large grain size of copper phthalocyanine deposited on PET-ITO substrates, with better carrier transport performance under illumination, and the ITO film reflects the infrared light, which increases the path of infrared light and leads to the enhancement of light absorption efficiency of photosensitive layer. The flexible NIR-II PT with Au-NPs layer obtains the maximum photoresponsivity of 5.54 A/W, the ON-state maximum light/dark current ratio of 13.1, and the specific detection rate ( D $^\ast$ ) of 6.82 $\times$ 10 $^{\text{11}}$ Jones, which maintains 72.7% photoelectric performances after 2000 flexural tests. The near-infrared hyperchromic effects of CTCs based on the organic/metal-oxide hybrid system provide more options for NIR-II light detection. Both of the phototransistors (PT) prepared on rigid and flexible substrates by using this CTC films achieve better performances. This indicates that the flexible infrared detectors based on the organic/metal-oxide CTC films have great potential for the future applications in wearable consumer electronics and healthcare.