Carbon nanohorn (CNH) is derivative from single-walled carbon nanotube (SWCNT) with a horn-like structure. Since hole-opened CNH aggregates (CNHoxs) are dispersible even in water, it can be promising materials for large scale optoelectronic devices fabricated with coating technique. We prepared CNHoxs-PSS composite films and studied its optoelectronic properties. We found good rectifying behaviors at the junction between CNHoxs-PSS and ITO. Significant photoresponse was observed when infrared (IR) light pulse was irradiated to the junction. Peak intensity of the photosignal increased with increment of bias voltage applied at the junction, while relaxation time decreased. When using thick cast films, even for zero bias, we observed significant photosignal, which increased proportionally with IR light intensity. Carrier mobility was estimated to be 3.5 x 10(-9) cm(2) V-1 s(-1) from the bias dependence of relaxation time of photosignal for thin spin coated films. This low value is ascribable to the hopping conduction between CNHoxs dispersed in PSS matrix. (C) 2020 The Japan Society of Applied Physics