Dielectric surface-dependent photogating phenomenon in C8-BTBT leading to broad spectral ultraviolet to near-infrared photoresponse and linearly-weighted synaptic phototransistors

Conventional organic phototransistors (OPTs) studies focus on the development of organic semiconductor layers to improve the photoresponsive characteristics. However, exploring a desirable dielectric surface is also an important factor in determining these photoresponsive characteristics in OPTs. This study investigates the dielectric surface-dependent broadband photoresponsive behaviors of C8-BTBT phototransistors and simulates optoelectrical artificial synapse behavior with SiO₂-based OPT. Photogating effect is observed depending on the trap states between C8-BTBT and various dielectric interfaces: CYTOP, PMMA, Al₂O₃, and SiO₂. No photogating effect is observed in the hydrophobic dielectric based OPTs, whereas shifts of turn-on voltage (V_turn-on) toward positive gate bias are observed in the hydrophilic dielectric based OPTs. The V_turn-on of SiO₂-based OPTs is shifted by up to 43 V under 400 nm light irradiation, achieving high sensitivity of >1.74 × 10⁴ A∙A⁻¹ and detectivity of >2.40 × 10¹² Jones. In the hydrophilic dielectric based OPTs, devices are characterized in ultra-broad optical range from the ultraviolet (UV) to near-infrared (NIR). In addition, optoelectrical artificial synaptic simulation with SiO₂-based OPT accomplishes a recognition rate of more than 95%, whereas, despite the same semiconductor, CYTOP-based OPT accomplishes a recognition rate of 0%.